{"Bibliographic":{"Title":"The Boulder Low-Level Intercomparison Experiment","Authors":"","Publication date":"1980","Publisher":""},"Administrative":{"Date created":"08-17-2023","Language":"English","Rights":"CC 0","Size":"0000360726"},"Pages":["or\n36\nNOAA/ERL Wave Propagation Laboratory\nb.2\nJune 1980\nBoulder, Colorado\nNational Center for Atmospheric Research\nTHE BOULDER LOW-LEVEL\nINTERCOMPARISON\nEXPERIMENT\nPreprint of WMO Report\nAOB","QC\n851\nB6\n692\nTHE BOULDER LOW-LEVEL\nINTERCOMPARISON\nEXPERIMENT\nPreprint of WMO Report\nEditors:\nJ.C. Kaimal\nH.W. Baynton\nJ.E. Gaynor\nReport Number Two\nJune 1980\nLIBRARY\nNOAA/NCAR\nBoulder Atmospheric Observatory\nJAN 20 1984\nN.O.A.A.\nU. S. Dept\nof Commerce\nA joint publication of NCAR and NOAA available from NOAA/ERL, Boulder, CO 80303, and from the NCAR\nPublications Office, P.O. Box 3000, Boulder, CO 80307.","NOTICE\nMention of a commercial company or product does not con-\nstitute an endorsement by NOAA Environmental Research\nLaboratories. Use for publicity or advertising purposes\nof information from this publication concerning proprie-\ntary products or the tests of such products is not au-\nthorized.\nThis report is to be published in a series\nof the World Meteorological Organization\nFor sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402\n(Order by SD Stock No. 003-017-00480-5)","FOREWORD\n(to be added by WMO)\niii","","PREFACE\nIn preparing this report for the WMO Commission for Instruments and\nMethods of Observation (CIMO), the editors have aimed at providing adequate\ncoverage of all three aspects of the Boulder Low-Level Intercomparison Experi-\nment (BLIE) the workshop preceding the experiment, the experiment itself,\nand the results of the intercomparison. Papers presented at the workshop form\nthe first part of the report, Chapters 1-23. The description of the experi-\nment in Chapter 24 reflects the perspective of the three members of the orga-\nnizing committee who planned and directed the experiment. Chapter 25, pre-\npared by the same three authors, describes the results and includes comments\nfrom participants on the performance of their sensors and explanations for\npossible discrepancies in their results. Here we have tried to remain faith-\nful to the spirit of the discussion session held at the end of the experiment,\nwhen preliminary results from the experiment were first examined and discussed.\nOur objective is to improve the present understanding of low-level sounding\ntechniques, not to rank sensors according to performance.\nThe experiment was conducted in August and September 1979 at the\nBoulder Atmospheric Observatory (BAO), located 25 km east of Boulder, Colorado.\nIt was divided into the following phases:\n(1) Checkout and preparation, 20-22 August.\n(2) Workshop, 23-24 August.\n(3) Comparison tests, 27 August-5 September.\n(4) Discussion session, 6 September.\nScientists from the National Oceanic and Atmospheric Administration\n(NOAA) of the U.S. Department of Commerce and from the National Center for\nAtmospheric Research (NCAR) collaborated in the planning and direction of all\nphases of the experiment. The BLIE organizing committee consisted of the\nfollowing members: J. C. Kaimal, Chairman (NOAA), H. W. Baynton (NCAR), J. E.\nGaynor (NOAA), F. G. Finger (NOAA), W. U. Weimann (WMO/CIMO), and H. P.\nTreussart (WMO/CIMO).\nReaders of this report will note that three of the measuring tech-\nniques described at the workshop were not tested during the experiment. The\ndescriptions of those techniques contain data from an experiment conducted at\nthe same site a year earlier under very similar conditions (Project PHOENIX,\nSeptember 1978). The instrumented aircraft, tal-Doppler radar, and passive\nradiometry techniques required such extensive data processing that guidelines\nimposed on other participants for data submission could not be applied to\nthem. Nevertheless, those techniques were considered important enough to be\nincluded in the workshop.\nParticipation in BLIE required that processed data be submitted\nwithin 24 hours of any operating period or that analog voltages be made avail-\nable for real-time sampling and processing on the BAO data-acquisition systems.\nWithout these restrictions the discussion session held after the experiment to\nevaluate the results would not have been possible. Years of delay, disagree-\nments, and frustrations over the outcome can be expected when participants do\ntheir processing after returning home from the experiment.\nEleven member nations of WMO participated in the experiment with\nequipment or as observers. Both the visitors and the resident staff of NOAA\nand NCAR cooperated to make this complex operation a success. Many of them\nput in long hard hours in the field. We take this opportunity to express our\nV","gratitude to all the participants. We are happy to acknowledge the financial\nand moral support provided by NOAA management: Dr. Wilmot N. Hess, Director,\nEnvironmental Research Laboratories, and Dr. C. Gordon Little, Director, Wave\nPropagation Laboratory. Facilities for holding the workshop and discussion\nsessions were generously provided by NCAR management: Dr. Francis P.\nBretherton, President, UCAR, and Dr. John W. Firor, Executive Director, NCAR.\nWe are also grateful to WMO for financial assistance extended to participants\nwho would otherwise have been unable to attend, and to the participating or-\nganizations and member nations for their strong endorsement of this compar-\nison. An experiment of this magnitude would not have been possible without\nthe full support and commitment of resources that accompany such endorsement.\nJ. C. Kaimal\nH. W. Baynton\nJ. E. Gaynor\nEditors\nvi","CONTENTS\nPage\niii\nForeword (to be added by WMO)\nV\nPreface\nPart 1\nPROCEEDINGS OF THE BLIE WORKSHOP\n1. BAO Sensors for Wind, Temperature, and Humidity Profiling\n1\nJ. C. Kaimal\n2. Single-Head Sonic Anemometer-Thermometer\n7\nT. Hanafusa, Y. Kobori, and Y. Mitsuta\n3. Vaisala Eight-Level Instrumented Tower System\n14\nI. Ikonen\n4. Remotely Piloted Aircraft for Atmospheric Soundings (SAM)\n18\nD. Martin\n5. Comparison of Aircraft and BAO Tower Measurements\n26\nD. H. Lenschow and B. B. Stankov\nTethered Aerodynamically Lifting Anemometer (TALA)\n6.\n33\nC. F. Woodhouse\nRemote Acoustic Electronic Sounding (RACES)\n7.\n38\nP. Ravussin\n8. FM-CW Radar\n47\nR. B. Chadwick and K. P. Moran\n9. Dual-Doppler Radar\n50\nR. A. Kropfli\n10. Remote Sensing of Temperature Profiles with Combined Active and Passive Sensors\n59\nM. T. Decker\n11. WPL Doppler Sounder\n63\nW. D. Neff, H. E. Ramm, and C. Wendt\n12. Doppler Acoustic System for Wind Profiling (AVIT)\n70\nP. MacCready\n13. Radian Corporation Model 800 Echosonde\n77\nM. A. McAnally\n14. Swedish Sodar System\n81\nS. Salomonsson and M. Hurtig\n15. The XONDAR\n87\nR. L. Peace, Jr.\n16. GMD-1 Radio Wind Sounding System\n98\nR. B. McBeth\nvii","17. TDFS Low-Level Radiosonde System\nC. Fink, E. Schöllmann, and A. Kolbl\n100\n18. CORA Radiosonde System Using Free-Flying Balloons\nI. Ikonen\n105\n19. The Airsonde System\nD. B. Call and A. L. Morris\n108\n20. The Tethersonde System\nA. L. Morris and D. B. Call\n117\n21. Tethered Balloon Profiler System\nK. Stefanicki\n125\n22. Boundary Layer Packages for Tethered Balloon\nM. Hayashi and 0. Yokoyama\n128\n23. NCAR Boundary Profiler System\nR. B. McBeth and S. Semmer\n136\nPart 2\nEXPERIMENT AND SUMMARY OF RESULTS\n24. Details of the Experiment\nJ. C. Kaimal, J. E. Gaynor, and H. W. Baynton\n140\n25. Summary of Results\nJ. C. Kaimal, J. E. Gaynor, and H. W. Baynton\n153\nviii","Figure 1.1. Instrumented 300-m tower at the BAO site.","1. BAO SENSORS FOR WIND, TEMPERATURE, AND HUMIDITY PROFILING\nJ. C. Kaimal\nNOAA/ERL/Wave Propagation Laboratory\nBoulder, Colorado, U.S.A.\nINTRODUCTION\n1.1\nThe Boulder Atmospheric Observatory (BAO) is a research facility operated jointly\nby NOAA's Wave Propagation Laboratory and the National Center for Atmospheric Research\n(NCAR). It is designed to provide high-quality measurements for use in boundary layer\nstudies and instrument calibration. Located on gently rolling terrain 25 km east of Boulder,\nits main feature is a 300-m tower (Fig. 1.1) instrumented at eight levels to measure the\nmean and turbulent properties of atmospheric parameters such as wind speed, wind direction,\ntemperature, and humidity. In-situ and remote sensors deployed around the tower provide\nadditional information on the structure of the flow (e.g., pressure fluctuations at several\nstations, temperature structure from acoustic sounders, acoustic Doppler winds and wind\nconvergence from a triangular configuration of optical crosswind sensors). A computer at\nthe site processes information from these sensors for real-time printout of data summaries\nand archiving of raw data. Mean profiles of wind, temperature, and humidity for successive\n20-min periods are available routinely. This real-time processing capability was an impor-\ntant factor in the choice of a site for the Boulder Low-Level Intercomparison Experiment\n(BLIE). A brief description of the tower sensors, the handling of data, and the parameters\nlisted on the summary sheets can be found in the sections to follow. For more details of\nthe site, instrumentation, and data processing see Kaimal (1978).\nTOWER INSTRUMENTATION\n1.2\nFor BLIE, data from the eight instrumented levels on the tower (10, 22, 50, 100,\n150, 200, 250, and 300 m) will be used as reference for comparing results obtained from the\nvarious sounding techniques. At each level, the sensors are distributed between two booms,\none of which points approximately SSE (154°) and the other approximately NNW (334°) (Fig.\n1.2). The three-axis sonic anemometer and the fast- and slow-response temperature sensors\nare mounted on the SSE boom (Fig. 1.3). In the absence of strong downslope winds from the\nRocky Mountains, the winds blow generally from the southeast during the day, but from the\nwest or northwest during the night. The orientation of the SSE boom is therefore optimum\nfor daytime observations. A propeller-vane anemometer and a cooled-mirror dew point hy-\ngrometer are mounted on the NNW boom (Fig. 1.4).\nThree-Axis Sonic Anemometer\n1.2.1\nThe sonic anemometer used on the BAO tower uses a fixed orthogonal array; the two\nhorizontal axes are oriented along and perpendicular to the boom, while the vertical axis\nis mounted at the end of the boom directed away from the tower (Fig. 1.3). The acceptable\nazimuth range for vertical velocity measurement is much larger in this array than in the\nnon-orthogonal arrays described by Mitsuta (1974) and Kaimal et al. (1974) However, the\nhorizontal wind measurements fare less well in this arrangement. Distortions in the flow\nwithin the acoustic path due to the presence of transducers cause the velocity readings to\nbe underestimated when the wind direction is close to one of the anemometer axes. An\napproximate form for the velocity underestimation as a function of 0 (angle between the\nwind direction and the acoustic path) has been obtained from wind tunnel and atmospheric\ntests. The measured velocity component um approaches the true velocity component ut in\nthe range 75° > 0 > 90° but drops off linearly with 0 for angles less than 75° (Fig. 1.5).\nFor a path length-to-diameter ratio of 25, appropriate to the BAO array,","Figure 1.2. Details of the tower structure and booms.\nFor a path length-to-diameter ratio of 25, appropriate to the BAO array,\nO<O<75\n;\n(1.1)\n75 90.\n;\nThe correction is made on each data point sampled. While an arc tangent routine\ncan be used for a first order approximation of 0 (with wind components measured along the\ntwo horizontal axes), it is more efficient to compute ut and Vt using analytic expressions\ngiven below that very nearly approximate (1.1). Defining ut as the component more closely\naligned with the wind and Vt as the component normal to it,\n(1.2a)\nV\n(1.2b)\nm\nwhere\nC = 0.926 + 0.31/ R + 1.38)\n(1.3a)\nD = 2.112 - C ; D > 1\n(1.3b)\n= 1.0\n;\n1\nand\nR = u m\n.\n(1.3c)\nNo such correction is needed for the vertical velocity measurements. A detailed discussion\nof these and other aspects of sonic anemometer performance can be found in Kaimal (1979).\nThe sonic anemometer probes used on the tower include a mix of EG&G (Model 198-2)\ntwo-axis - probes, Ball Brothers (Model 125-198) two-axis probes, and Ball Brothers (Model\n2","Figure 1.4. Propvane and dew point hygrom-\nFigure 1.3. Three-axis sonic anemometer\neter on NNW boom.\nand slow-response quartz thermometer in\naspirated shield on SSE boom.\n125-197) single-axis probes. Driver and receiver circuits associated with the probe are\nlocated in waterproof boxes at each level on the tower; coaxial cables connect these cir-\ncuits to the computer interface circuits located in the van at the base of the tower. fired To\ninsure proper synchronization in data-sampling the transmitters at all levels are\nsimultaneously. The firing proceeds at 200 Hz, exactly 20 times the sampling rate (10 the Hz)\nfor all the fast-response channels. The interface circuit automatically accumulates\nreadings from 20 successive transmissions before transferring the data to computer memory.\nThis block-averaging is provided to minimize aliasing in the spectral computations.\nPropeller-Vane Anemometer\n1.2.2\nA ruggedized version of R. M. Young Co.'s propeller-vane anemometer, Propvane\nModel 8002, is used. The polystyrene propeller in this model has a distance constant of\n2.4 m and a working range from 1 to 54 m/s. Calibration of the wind speed output is ac-\ncomplished by driving the propeller shaft at a known rate of rotation (1800 rpm) and ad-\njusting the voltage level to the corresponding wind speed indication (15 m/s).\nThe vane position is indicated by a precision conductive plastic potentiometer\nconnected to the vane shaft. The potentiometer has a deadband of 18°. This deadband is\npointed in the direction of the tower so that the active range of the potentiometer coin-\ncides with the azimuth range of best exposure for the NNW boom. Data for azimuth wind\ndirections between 110° and 180° are often degraded by a combination of the tower inter-\nference and the voltage jump produced by passage of the potentiometer brush across the\ndeadband.\nFluctuating Temperature Sensor\n1.2.3\nA platinum wire thermometer (AIR Inc. Model DTIA), mounted within the frame of\nthe sonic anemometer's vertical axis probe, measures fluctuations in the temperature with a\n3","1.1\n1.0\nd\n50\n=\na\n0.9\n25\n15\n0.8\n10\nV\n0.7\nUt\n0\nd\n0.6\n-80\n-60\n-40\n-20\n0\n20\n40\n60\n80\n0 (degrees)\nFigure 1.5. Attenuation in measured sonic wind velocity component from flow\ndistortions along the acoustic path caused by the transducers. The heavy\nline corresponding to d/a = 25 is the response curve for the BAO sonic\nanemometer.\nfrequency response comparable with the path-averaged response of the sonic anemometer. The\nsensor consists of a length of 12- platinum wire (nominal resistance of 150 S2) wound\naround is a helical bobbin. This wire is part of a simple bridge circuit the output of which\namplified by a low-noise, low-drift circuit to provide an output voltage of + 10 V\ncorresponding to a temperature range of + 50°C.\n1.2.4\nSlow-Response Temperature Sensor\nAbsolute measurements of air temperature are made with a Hewlett Packard quartz\nthermometer (Model 2850A) housed in an R. M. Young aspirated shield (Model 43404). The\nsensor tion is accurate to within 0.005°C, but has a long time constant, about 1 min. Calibra-\nficant checks performed over the years in the same precision temperature bath show no signi-\nvariation in the thermometers' calibration constants with time.\n1.2.5\nDew Point Sensor\nA Cambridge Systems aspirated cooled mirror hygrometer (Model 110-SM), calibrated\nof as recommended by the manufacturer, measures the dew point at each level. The temperature\na mirror, made to track the dew point (or frost point) temperature, is measured. The\ncycling time for temperature control is approximately 1 S.\n1.3\nDATA ACQUISITION AND DISPLAY\nAcquisition of data from the sensors is controlled by a PDP 11/34 computer at the\nBAO\nsite. The data acquisition system samples the fast-response sensors at the rate of 10\n4","BOULDER ATMOSPHERIC OBSERVATORY DATA SUMMARY\n5 SEP 79 10 20 MST\nAVERAGING PERIOD= 20.00 MIN\nT\nTD\nL\nPVS\nPVD\nVH\nAZ\nW\nU\nV\nZCMI\nUWES\nVSOU\n-25.77\n28.19\n1.30\n4.42\n55.\n4.73\n43.\n4.41\n-0.18\n-3.46\n-1.69\n-30.21\n10\n-3.22\n27.64\n0.63\n4.88\n54.\n5.19\n41.\n-2.07\n4.76\n-0.10\n22\n-3.37\n-3.95\n27.12\n0.43\n-63.04\n4.98\n51.\n5.33\n40.\n-0.18\n-2.16\n4.88\n-80.50\n50\n-3.44\n-4.08\n26.59\n0.40\n5.05\n54.\n5.58\n43.\n-1.98\n5.22\n-0.08\n-4.07\n100\n-3.82\n999.99\n26.06\n-0.20\n5.24\n54.\n5.46\n46.\n5.20\n-0.16\n-3.96\n-3.76\n-1.64\n150\n25.48\n-0.49\n999.99\n5.23\n56.\n50.\n-0.05\n5.15\n-1.27\n5.00\n200\n-3.94\n-3.33\n25.06\n-0.99\n999.99\n5.24\n53.\n5.50\n48.\n5.30\n-0.11\n999.99\n-3.65\n-1.48\n24.56\n-1.34\n250\n-4.11\n5.50\n53.\n5.57\n46.\n5.29\n-0.11\n-3.88\n-1.73\n300\n-4.00\nUW\nWT\nUW\nUT\nVT\nUV\nWW\nTT\nZEMJ\nUU\nUV\n-0.0999\n-0.1314\n0.1623\n-0.2360\n-0.4158\n-0.0337\n0.2380\n0.3675\n10\n1.4315\n0.9045\n0.1685\n-0.0811\n-0.1500\n-0.0682\n-0.1432\n0.1983\n-0.3042\n0.7045\n0.3757\n0.1352\n22\n1.2687\n-0.0239\n-0.2118\n-0.0946\n-0.2340\n-0.0809\n0.6504\n0.0778\n0.1057\n50\n1.0214\n0.5257\n-0.0195\n-0.2118\n-0.0856\n-0.0233\n-0.0877\n0.7717\n0.0548\n0.7430\n0.6420\n100\n-0.1297\n0.0727\n-0.0186\n-0.0716\n-0.0697\n0.0285\n0.0889\n0.7280\n0.7761\n-0.1253\n0.0454\n150\n0.8567\n-0.0391\n-0.0658\n-0.0354\n-0.0859\n0.6753\n0.0211\n0.9299\n0.7570\n200\n-0.0707\n-0.2243\n0.0325\n-0.0650\n0.0294\n-0.0433\n0.7471\n0.0284\n250\n1.1671\n0.8311\n-0.0995\n-0.0086\n-0.0631\n-0.1268\n0.0473\n-0.0126\n0.0264\n0.8532\n0.5918\n300\n0.8392\nRMS PRESSURE VALUES [MICROBARS]\nOPTICAL TRIANGLE\nSTN 4\nSTN 5\nSTN 1\nSTN 2\nSTN 3\nLOG10(CN2)\nCONV [1/SEC]\nv [M/SEC]\nAZ [DEG]\n19,247\n8.690\n7.832\n6.597\n6.461\n13.14339161\n0.01118\n1.25\n13.\nSOLAR RADCLY/MIN]\nPRESSUREEMB]\n1.07\n842.25\nFigure 1.6. Sample listing of summary data for a 20-min averaging period. The\ntime\nindicated at top right refers to the beginning of the averaging period. Column heads\nare explained in Table 1.1.\nHz and the slow-response sensors at 1 Hz. Real-time computations of means, variances,\ncovariances, and Obukhov lengths are made for consecutive 20-min periods (starting on the\nhour) and are listed on the line printer at the end of each averaging period. The summar-\nies are recorded on magnetic tape along with a compressed form of the time series.\nTo minimize tape storage requirements, only 10-s averages and 10-s grab samples\n(last sample in each 10-'s averaging period) of the ast-response time series are stored.\nOn the slow-response channels no attempt is made to save the 10-s grab samples. High-\nfrequency information in the form of smoothed spectral estimates (approximately 10 esti-\nmates per decade) is stored for later use in extending spectra computed from the 10-s\naveraged data points. For this intercomparison experiment only the results from the\nsummary sheets will be used. A sample listing for one period is shown in Fig. 1.6; Table\n1.1 explains the symbols.\nThe parameters relevant to this experiment (VWES, VSOU, W, VH, AZ, T, and Id) will be\nlisted separately for comparison with data from systems operated by other participants.\nTo minimize possible tower influence on the wind data, sonic anemometer readings will be\nused only for azimuth wind directions 64° - 154° (CW) For wind directions 154° - 64°\n(CW) the Propvane readings will be used instead.\n5","Table 1.1. Explanation of terms used on BAO data summary sheet (Fig. 1.6)\nZ(M)\nHeight (meters)\nAVERAGED PARAMETERS (SI units)\nVWES\nHorizontal wind component from west (sonic)\nVSOU\nHorizontal wind component from south (sonic)\nU\nHorizontal wind component along the X axis, from 154° (sonic)\nV\nHorizontal wind component along the y axis, from 64° (sonic)\nW\nVertical wind component (sonic)\nVH\nHorizontal wind speed (sonic)\nAZ\nHorizontal wind direction (sonic)\nPVS\nHorizontal wind speed (propvane)\nPVD\nHorizontal true wind direction (propvane)\nT\nTemperature (quartz thermometer)\nTD\nDew point (dew point hygrometer)\nL\nObukhov length\n2nd MOMENTS (SI units)\nUU, VV, WW, TT, UV, UW, UT, VT, UW, and WT\nU\n(=u) Longitudinal wind component (sonic)\nReferenced to 10 m\nV\n(=v) Lateral wind component (sonic)\nmean wind direction\nW\n(=w) Vertical wind component (sonic)\nT\n(=0) Temperature (platinum wire)\nOPTICAL TRIANGLE (SI units)\nV\nWind speed\nFrom measurements along\nAZ\nWind direction (CW)\nlegs of an equilateral\nCONV\nConvergence\ntriangle, 450 m on each\nOG10(CN2)\nStructure parameter for\nside, centered on tower\nrefractive index X 1012\nRMS PRESSURE VALUES (microbars)\nFrom pressure fluctua-\n(STN 1 STN 5)\ntion stations around\nthe tower\nPRESSURE (mb)\nMean surface pressure\nSOLAR RAD (Langleys/min)\nMean solar radiation\n(direct and diffuse)\n1.4\nREFERENCES\nKaimal, J. C. (1978): NOAA instrumentation at the Boulder Atmospheric Observatory.\nPrepr. Vol. 4th Symp. on Meteorol. Obs. and Instrum., 1978, Denver, Colo., , American\nMeteorological Society, Boston, Mass., , pp. 35-40.\nKaimal, J. C. (1979): Sonic anemometer measurement of atmospheric turbulence. Proc.\nDynamic Flow Conf., 1978, Baltimore, Md., , DISA, P.O. Box 121, Skovlunde, Denmark,\npp. 551-565.\nKaimal, J. C. , J. T. Newman, A. Bisberg, and K. Cole (1974): An improved three-component\nsonic anemometer for investigation of atmospheric turbulence. In Flow: Its Measurement\nand Control in Science and Industry, Vol. 1, Proc. of a Symp., , 10-14 May 1971,\nPittsburgh, Pa., Rodger B. Dowdell (ed.), Instrument Society of America, Pittsburgh,\npp. 349-359.\nMitsuta, Y. (1974): Sonic anemometer-thermometer for atmospheric turbulence measurements. In\nFlow: Its Measurement and Control in Science and Industry, Vol. 1, Proc. of a Symp\n10-14 May 1971, Pittsburgh, Pa., , Rodger B. Dowdell (ed.), Instrument Society of\n,\nAmerica, Pittsburgh, pp. 341-348.\n6","2. SINGLE-HEAD SONIC ANEMOMETER-THERMOMETER\nTatsuo Hanafusa\nMeteorological Research Institute\nJapan Meteorological Agency\nTsukuba, Japan\nYasuhiro Kobori\nKaijo Electric Co.\nTokyo, Japan\nYasushi Mitsuta\nDisaster Prevention Research Institute\nKyoto University\nKyoto, Japan\nINTRODUCTION\n2.1\nA sonic anemometer-thermometer detects by sonic means the wind velocity component\nand the air density or temperature along the sound path. The first successful sonic\nanemometer-thermometer for use in the atmospheric turbulence studies was developed by\nSuomi (1957). In his instrument, velocity and temperature fluctuations were obtained by\nthe difference and sum of transit times for two series of sound pulses traveling in oppo-\nsite directions along the same sound path.\nAmplitude variations in the received pulse signal of Suomi's instrument caused\nerrors in transit time detection. To avoid such errors, Kaimal and Businger (1963) of the\nUniversity of Washington developed a continuous-wave sonic anemometer-thermometer which\nmeasured phase shifts between the two signals received at either end of the sound path.\nTheir instrument gave satisfactory performance in field observations.\nImprovement of the pulse-type instrument continued at Kyoto University, and a\npractical instrument was completed by Mitsuta (1966). The instruments, developed independ-\nently by the University of Washington and Kyoto University, when compared in the United\nStates in 1965 showed excellent agreement in the measured wind velocity component (Businger\net al., 1969).\nAfter discussions of the merits of the instruments, the two groups decided to\ndevelop a new three-dimensional sonic anemometer-thermometer of pulse type as a joint\neffort. The pulse-type instrument appeared more promising for absolute measurement of\npulse transit times and for attaining wide observation range and stable zero point, if\nonly a reliable means of transit-time detection could be developed. Subsequent development\nof a new technique to determine the time of reception of the signal pulse (by making the\ntrigger pulse from the third wave of received signal pulse instead of the wave envelope)\nenabled the Japanese group to produce a new solid state three-dimensional sonic anemometer-\nthermometer (Mitsuta et al., 1967). After several improvements a more refined version\nwith three 20-cm sound paths and using 100-kHz acoustic pulses was completed (Mitsuta,\n1974). It was widely and successfully applied in various field experiments as reported by\nJapan-U.S. Joint Study Group (1971) and has been produced commercially in Japan.\nThrough almost a decade of practical application of this instrument, we have\nidentified major sources of unreliability. One important source was zero-point drift\ncaused by small variations in the geometrical length of sound paths. Small differences in\nlength between two opposite sound paths cause large zero offsets in the two-head type\nanemometer. The other source of unreliability arose from the temperature and cross wind\napproximations in the derived wind and temperature. The new single-head sonic anemometer-\nthermometer described by the present authors achieves more reliable measurement by removing\n7","5\n(\nB\nW\n120\nB\n200\n400\n(b)\nW+\nA\n0\n<<<<<\nB+\nB1\nw\nFigure 2.1. The new single-head anemo-\nmeter-thermometer: a) wind antenna\nspecifications; b) main chassis, junc-\ntion box, and wind antenna (from left\nto right).\n(a)\nthe difficulties mentioned above. The basic points of improvement from the 1971 model are\nadoption of a more precise formula for processing, a single-head two-way sound path, and a\nmore effective noise-gate circuit.\n2.2\nBASIC PRINCIPLES\nThe transit time of a sound signal traveling from one end of the sound path to\nthe other separated by distance d can be written as follows (Schotland, 1955):\n= (c2 v v2, 1/2 + Vd .\nt\nd\n(2.1)\nC2\nv2\n-\nwhere V is total wind velocity, Vd and V n are wind velocity components in the directions\nparallel and normal to the sound path, and C is the velocity of sound in still air. The\nsign, +, before Vd should be chosen according to the direction of sound transmission.\nIf two transit times t1 and t2 in opposite directions on the same sound path are\ndetected, Vd can be obtained independent from V and Vn as follows:\nthe\n1\n(2.2)\n8","C can be obtained by assuming C2 >> V2 as follows:\n(2.3)\n.\nThe velocity of sound in still air, C, can be expressed as follows (Barret and Suomi,\n1949):\n20.067T 1/2 ,\n(2.4)\nC =\nSV\nwhere Isv is sound virtual temperature of the air and is equal to air temperature if the\natmosphere is dry. In moist air Isv can be correlated with air temperature, T, by water\nvapor pressure, e, as follows:\n(2.5)\nTey = T(1 + 0.3192e/p)\nwhere p is atmospheric pressure.\nThen Isv can be obtained from two transit times t1 and t2 by the following\nequation:\n14/12/2020\n(2.6)\nIn the present instrument, the pulse transit times are processed electronically\nfollowing (2.2) and (2.6) to obtain the wind velocity and virtual temperature outputs.\nThe wind velocity component obtained by equation (2.2) is the line-averaged wind\nvelocity component over the sound path of length d in the direction parallel to it; air\ntemperature obtained by (2.6) is also sound virtual temperature averaged over the sound\npath, d. Those are apparently smoother than the point-detected entities. The attenuation\ncharacteristics of this line averaging were studied by Mitsuta (1966) and in more detail\nby Silverman (1968).\nDESCRIPTION OF THE INSTRUMENT\n2.3\nThe new three-dimensional sonic anemometer-thermometer is shown in Fig. 2.1, and\na block diagram of its functions is shown in Fig. 2.2. The sensor (wind antenna) has two\nhorizontal sound paths (A,B) crossing at 120° and a vertical sound path (W); at both ends\nof each path are two-way sound transducers which perform alternately as transmitter and\nreceiver. The switching circuit, transmitter, and pre-amplifiers are built in the junction\nbox located near the sensor. The main chassis consists of a main oscillator, a main\ncontroller, transit time detection circuits, wind velocity converters, a temperature\nconverter and a power supply. All components are solid state, many of them being inte-\ngrated circuits.\nThe main oscillator is a crystal oscillator of 5.5556 MHz. It supplies the\nclock signals for wind calculation (5.5556 MHz), and for temperature calculation (2.7778\nMHz), and the timing signal to the main controller which generates timing signals (110 Hz,\nsix times the observation cycle) to switch transducers and to trigger noise gates and\nconverting circuits. The lead-zirconate transducers at both ends of the three sound paths\n(A,B,W) are triggered alternatively in the sequence of A+, A-, B+, B-, w+ and W at equal\n9","TRANSMITTER\nA+\nTR\nPRE-AMP\nW\nsound path\nB +\nA\ntransducer\nW\nB-\nWIND ANTENNA\nJUNCTION BOX\nMAIN CHASSIS\nAMPLIFIER\nA+ A B+ B W+ W\nNOISE GATE\n~ 50,US\nZERO\nADJUST\nreceived wave form\n3rd WAVE\nDETECTION\nMAIN\nTRANSIT TIME\nTEMPERATURE\nSIGNAL GEN.\nCOUNTER 1\nCONTROLLER\nINVERSE\nSQUARE\nMAIN\nCALCULATION\nCIRCUIT\nOSCILLATOR\nTEMPERATURE\nWIND COUNTER\nCALIBRATION\nCOUNTER 2\nD/A CONVERTER\n300V +15V -15V\nD/A CONVERTER\nA\n1\n1\nPOWER\nSUPPLY\nOUT\nOUT\nOUT\nOUT\nA\nB\nW\nDIGITAL\nANALOG\nANALOG\nDIGITAL\nWIND OUT WIND OUT\nTEMP. OUT\nTEMP. OUT\nAC 100V\nFigure 2.2. Block diagram of the new single-head anemometer-\nthermometer.\nintervals, clocked by the timing signal. The transducers, when triggered, send out burst\nsignals at resonant frequency of 100 kHz. When the transducer at one end of the sound\npath is triggered, the transducer at the opposite end of the path switches to its receiving\nmode.\nThe received signals sent to the receiver amplifier are first separated from the\nnoise by noise gates, then shaped and triggered at the zero crossing point of the third\nwave to generate the receipt time signal pulse. The transmitting pulse delayed to adjust\nfor the zero point and the receipt time signal pulse are supplied to the inverse calcula-\ntion circuit which produces the signal pulse whose width is proportional to the inverse of\nthe pulse transit time of each sounding.\nThe counter for the wind velocity component is an up-down counter clocked by\n5 .5556 MHz to make the difference of width of the signal pulses corresponding to the\n10","Table 2.1. Specifications of the new sonic anemometer-thermometer\nThermometer\nAnemometer\nTime-sharing multiplex transmission/reception switchover type\nMeasuring mode\nultrasonic pulse emission, ~ 20 Hz per channel.\nCentral temperature: -10° ~ 40°C\n+30 m/s\n0\n~\nMeasuring range\nTemperature deviation: 0 2 +5°C\n1%\n1%\nAccuracy\n0.025°C\n0.5 cm/s\nMinimum resolution\n10 Hz\n10 Hz\nFrequency resolution\nOUT 1: 0 to +1 V/+50°C\nOUT 1: 0 to +1 V/10m/s 8 V max\nOUT 2: 0 to +1 V/+5°C\nOUT 2: 0 to +1 V/full scale\nFull scale *U:+5, +10, +25, +50 m/s\nAnalog output\n**W:+1, +2, +5, +10 m/s\n12 bit binary code\n15 bit binary code\nDigital output***\nProbe and junction box: -20° to 50°C\nMain unit: -10° to 40°C,\nOperating temperature\n50/60Hz\nAC 100/115/220 V +10%\nPower supply\n*U: Horizontal component.\n**W: Vertical component.\n***Not used in the present intercomparison.\nsuccessive two soundings in the opposite directions on the same sound path, such as A+ and\nA-, B+ and B-, and W+ and W. One bit in this counter corresponds to 0.005 m/s. The\ndigital signal corresponding to the difference is converted into a voltage analog signal\nin a D-A converter and then distributed to each wind component output circuit.\nThe first counter in the temperature circuit produces a voltage analog signal\nproportional to the sum of the two successive soundings in opposite directions on the\nvertical sound path (w+ + w-) This voltage is squared, producing a temperature signal\npulse whose width is proportional to sound virtual temperature. The width of the tempera-\nture signal pulse is converted into a temperature digital signal by the second counter\nclocked by a 2.778 MHz signal from the main oscillator. One bit in the temperature cor-\nresponds to 0.025°C The digital signal is converted to an analog temperature output\nthrough a D-A converter.\nDigital techniques were adopted in the pulse-width detecting circuit to attain\nhigh accuracy and stability of measurement. Hybrid systems of digital and analog circuits\nhave been replaced by pure digital processing systems.\nPERFORMANCE\n2.4\nAll of the circuit parameters can be tested and adjusted electronically within\ntheir limits of tolerance, except the aeroacoustic characteristics of the wind antenna.\nThe specifications of the new sonic anemometer-thermometer are as shown in Table 2.1.\nThe aeroacoustic characteristics of the wind antenna were tested in the wind\ntunnel of MRI. The length of the sound path is 20 cm, and the diameter of the transducer\nis about 1.5 cm. Therefore the wake to the lee of the transducer produces some errors in\nmeasurement even though streamline shape of the transducer is improved. The horizontal\nwind speed component detected by each leg of horizontal sound path for various wind direc-\ntion to the wind antenna is as shown in Fig. 2.3. The crossing angle of the leg is 120°,\n11","U(m/s)\n5.0\nU\n'A\nUB\n4.0\n0\n$3.0\nas\n2.0\n1.0\n-100°\n-50°\n50°\n100°\n-1.0\n-1.0\n3.0\n-4.0\n-5.0\nFigure 2.3. Directional characteristics of the two horizontal legs of the wind antenna.\nand wind is just along the direction of each leg when wind direction is +60° o A small dip\nof the output can be seen at this angle as seen in this figure, which is caused by the wake\neffect of the transducer. Therefore this antenna should be used in the wind direction\nrange of +45° from the central axis.\n2.5\nCONCLUDING REMARKS\nThe first device of the present type was completed in 1976 and first used in the\nfield observation of International Turbulence Comparison Experiment (ITCE) in Australia.\nThe improved version is now under commercial production. Six sets of them were installed\non the Meteorological Research Tower at Tsukuba and performed well for about one year.\nThe variation of this sonic anemometer-thermometer is a two-dimensional wind\nsensor with a coordinate converter to compute wind speed and direction. It will be valu-\nable for air pollution study in light wind conditions, because it can measure wind down to\n0.005 m/s without restrictions by mechanical inertia and friction under any weather condi-\ntions.\n12","2.6\nREFERENCES\nBarrett, E. W., and V. E. Suomi (1949) : Preliminary report on temperature measurement by\nsonic means. J. Meteorol. 6:273-276.\nBusinger, J. A., , M. Miyake, E. Inoue, Y. Mitsuta, and T. Hanafusa (1969) : Sonic anemometer\ncomparison and measurements in the atmospheric surface layer. J. Meteorol. Soc.\nJapan 47:1-12.\nJapan-U.S. Joint Study Group (1971): Development of sonic anemometer-thermometer and its\napplications to the study of atmospheric surface layer. WDD Technical Note No. 6,\nKyoto Univ., Kyoto, Japan, 250 pp.\nKaimal, J. C. and J. A. Businger (1963): A continuous wave sonic anemometer-thermometer\nJ. Appl. Meteorol. 2:156-164.\nMitsuta, Y. (1966) : Sonic anemometer-thermometer for general use. J. Meteorol. Soc.\nJapan 44:12-24.\nMitsuta, Y., M. Miyake, and Y. Kobori (1967): Three dimensional sonic anemometer-\nthermometer for atmospheric turbulence measurement. WDD Technical Note, Disaster\nPrevention Res. Inst., , Occasional Report, Kyoto Univ., Kyoto, Japan, 20 pp.\nMitsuta, Y., 1 (1974): Sonic anemometer-thermometer for atmospheric turbulence measure-\nments. Flow: Its Measurement and Control in Science and Industry, Vol. 1, Proc. of\na Symp., 10-14 - May 1971, Pittsburgh, Pa., , Rodger B. Dowdell (ed.), Instrument\nSociety of America, Pittsburgh, pp. 341-348.\nSchotland, R. M. (1955): The measurement of wind velocity by sonic waves. J. Meteorol.\n12:386-390.\nSilverman, B. A. (1968): The effect of spatial averaging on spectrum estimation. J.\nAppl. Meteorol. 7:168-172.\nSuomi, V. E. (1957): Sonic anemometer. In Exploring the Atmosphere's First Mile, Vol. 1,\nH. H. Lettau and B. Davidson (eds.), , Pergamon, N.Y., pp. 256-266.\n13","3. VAISALA EIGHT-LEVEL INSTRUMENTED TOWER SYSTEM\nIlkka Ikonen\nVaisala Oy\nHelsinki, Finland\n3.1\nINTRODUCTION\nThe tower-based wind-shear and temperature-inversion observing and warning\nsystem, Vaisala MIDAS 200, gives real-time data on Low-altitude atmospheric conditions\nnear an airport.\n3.2\nGENERAL SYSTEM DESCRIPTION\nThe main components of the MIDAS 200 system are described below:\n(1) Sensors. Sensors are provided for measuring temperature at eight levels,\nwind speed and direction at four levels, and humidity also at four levels of the\ninstrumentation tower. The number of sensor levels in the system is designed to\nadequately cover the first 300 meters of the atmosphere, which is considered high\nenough to provide sufficient information for air traffic, especially during landing\nand take-off. The sensor types and installation levels are specified in Tables 3.1\nand 3.2. Figures 3.1 and 3.2 show the sensors as installed on the BAO tower during\nBLIE.\n(2) Data processing unit. The heart of the system is a microprocessor-based\nprocessing unit. It measures the sensor output signals; computes and stores the\ncorresponding average, minimum, and maximum values; and finally provides the weather\ndata to the printer terminals and the cassette unit in a format specified by the\noperator. The processing system`runs on a 5-kilobyte program memory and 4-kilobyte\nbuffer storage memory. It is able to support two independent data terminals and a\ncassette drive.\n(3) Data output and operator terminals. Two 30-char/s printer terminals and a\nC-cassette drive are provided for data output, system control by operator, and data\nstorage.\nTable 3.1. Sensors in the instrumentation tower\nParameter\nSensor type\nQuantity\nSignal\nWires/sensor\ntype\nTemperature\nVaisala DTS 12, Pt 100\n8\nanalog\n3\nHumidity\nVaisala HMP 14 U, Humicap\n4\nanalog\n4\nWind speed\nVaisala WAA 12, anemometer\n4\nanalog\n3\nWind direction\nVaisala WAV 12, wind vane\n4\nanalog\n9\n14","Table 3.2. Sensor installation\nSignal wires required\nSensor*\nLevel\nDigital (WS, WD)\nAnalog (T, H)\nT\nH\nWS\nWD\n12\n7\nX\nX\nX\nX\n300 m\n7\nX\n250 m\n12\n7\nX\nX\nX\n200 m\n7\n150 m\n12\n7\nX\nX\nX\n100 m\n7\n50 m\n12\n7\nX\nX\nX\n22 m\n7\nX\n10 m\n*The analog sensor and the digital sensor must not be connected to the\nsame cable. Thus two cables are needed from the data processing unit\nto installation levels 22 m, 100 m, 200 m, and 300 m. All the cables\nshould be shielded. Cross section of 0.75 mm2 per wire is required.\nMEASURING AND COMPUTING THE PARAMETERS\n3.3\nAll the analog sensor signals (temperature and humidity) are measured at inter-\nvals of 30 S, and all the digital sensor signals (wind speed and direction) are measured\nat intervals of 2 S.\nAt the end of each 2-min period the following values are computed and presented\nas new data:\n(1) Temperature, 2-min average values (°C) for each sensor level.\n(2) Relative humidity, 2-min average values (%) for each sensor level.\n(3) Wind speed, both 2- and 10-min average, minimum, and maximum values (knots)\nfor each sensor level.\n(4) Wind direction, both 2- and 10-min average, minimum, and maximum values\n(degrees) for each sensor level.\n(5) Vertical wind shear values are determined by calculating the wind vector\nrelative differences between each two successive wind sensor levels and between the\nhighest and lowest levels. The shear values are computed on the basis of the 2-min\naverage wind values (ICAO recommendation) Only shear vector magnitudes are avail-\nable (knots/ 30 m)\n(6) To detect temperature inversions the temperature differences between each\ntwo successive sensor levels and between the lowest level and all the other levels\nare computed. (These together make 13 comparisons.)\nThe wind shear and temperature data are automatically given as an appropriate\nalarm message, if one or more of the shear values or temperature differences exceeds the\nalarm limits selected by the operator. All the other data are printed on request or at\ncertain time intervals determined by the operator.\n15","Figure 3.1. Vaisala cup and vane system\nFigure 3.2. Vaisala radiation shield\nmounted on SSE boom of BAO tower.\n(housing temperature and humidity\nsensors) mounted on NNW boom of BAO\ntower.\n3.4\nDATA OUTPUT AND STORAGE\nThe MIDAS-200 system supports two independent data terminals. The basic system\nincludes two 300-bits/s (30 char/s) printer terminals and a pair of 300-bits/s data modems\nfor use if the other terminal is installed more than 200 meters away from the processing\nunit.\nThe following types of data messages are sent to the printer terminals by simple\ncommands:\n(1) Wind data, direction/speed average values from each level (degrees/knots).\n(2) Wind data, direction/speed maximum-minimum values from each level (degrees/\nknots).\n(3) Vertical wind shear vector magnitudes between the highest and lowest levels\nand between each two successive levels, five values together (knots/30 m).\n(4) Temperature data from each level (°C).\n(5) Humidity data from each level (% RH).\n(6) Messages (4) and (5) together.\n(7) Messages (1) and (2) together.\n(8) Messages (1), (2), and (3) all together.\n(9) Messages (1) (5) all together.\n(10) Graphic profile of wind data: direction average and variation, speed average\nand variation (every level).\n16","(11) Like message (1), but for only one selected level.\n(12) Graphic profile of humidity data (every level).\n(13) Like message (12), but for only one selected level.\n(14) Graphic profile of temperature data (every level).\n(15) Like message (14), but for only one selected level.\nAll the message types above are available either on request or repeatedly at\nintervals. These intervals can be any number of 2-min increments from 1 to 255. All the\nmessages are provided with current date and time of the day.\nthe wind shear or temperature difference values exceed the corresponding\nIf\nalarm limits set by the operator, the message type (3) or (4) is automatically printed\ntogether with the alarm signal. Also an \"alarm-over\" message is sent as conditions come\nback to normal again.\nThe system stores in the memory the measured data at selectable time intervals,\nthus making it possible to compare the previous meteorological condition with the present\none. Like the reporting interval, the storing interval can be set in 2-min increments.\nMemory space for up to 33 separate data stores is provided.\nThe MIDAS-200 system also contains cassette recording equipment (C-cassette).\nAll the data are recorded at selectable intervals on the cassette. A cassette will hold\ndata for 50 days if the recording interval is 30 minutes. A separate cassette reader is\nneeded for transfer of data to other systems.\nSUMMARY\n3.5\nThis tower-based wind-shear and temperature-inversion observing and warning\nsystem, designed primarily for aviation services, can be used as an autonomous system\ngiving data directly to users or as a subsystem of a larger data-processing and distribu-\ntion system. The relevant ICAO recommendations are taken into account in the design.\n17","4. REMOTELY PILOTED AIRCRAFT FOR ATMOSPHERIC SOUNDINGS (SAM)\nDaniel Martin\nEtablissement d'Etudes et de Recherches Météorologiques (EERM)\nCentre de Recherches de Magny les Hameaux\n78470 Saint Rémy les Chevreuse, France\n4.1\nINTRODUCTION\nDuring the last three years the French Meteorological Research Department (EERM)\nhas developed small remotely piloted aircraft for atmospheric soundings. They are particu-\nlarly suited for boundary layer explorations. As atmospheric probes, the remotely piloted\naircraft have the advantage of high resolution, high repetition rate, low cost, the ability\nto make horizontal and vertical measurements and accessibility over difficult and high risk\nareas. Its limitations are those imposed by cruising range, ceiling, and visibility flight\nrules.\nThe EERM program that uses these devices is called Sondes Aerologiques Motorisées\n(SAM) The aircraft devices are designed for various applications. SAM-B provides aerolog-\nical soundings in the layer 0-500 m, with real-time measurements of pressure, temperature,\nand humidity. SAM-C has an operational ceiling of >4000 m with better capabilities (pay-\nload, ceiling, flight duration, aerodynamic self-stability) than the SAM-B. It allows for\nsimultaneous pressure, temperature, and humidity measurements and gas samplings.\n4.2\nSYSTEM DESCRIPTION\n4.2.1\nSAM-B\nSAM-B has a circular wing of polystyrene covered with kraft paper; the body\n(moulded fiber) contains the instruments. Its \"critical aerodynamics\" permit a parachute-\nlike descent, providing an easy and safe approach and landing, as well as good aerodynamic\nstability at low speed (10 m/s). The simplicity of the design provides low cost and easy\nmaintenance. Figure 4.1 shows SAM-B taking off. Limitations of this aircraft are as\nfollows:\n(1) It has a small visual range between pilot and aircraft (800 m) because of its\nsize and geometry.\n(2) Maximum wind it can be used in is 10 m/s.\n(3) Operational ceiling is about 2000 m.\nTo overcome these limitations, a SAM-D (Fig. 4.2) with a delta wing that has a\nfront stabilizer is currently being developed, allowing a wider speed range, a vertical\nspeed of about 7 m/s, an operational ceiling of 5000 m, and the ability to be used in\nwinds up to 15 m/s.\nCharacteristics of SAM-B and SAM-D are given in Table 4.1.\n4.2.2\nSAM-C\nSAM-C is a self-stabilizing motorized glider with modular design, made of poly-\nstyrene and fiberglass. A special feature of the aircraft (Fig. 4.3) is its inverted \"V\"\n18","Figure 4.1.\nSAM-B taking off.\n01\nFigure 4.2. SAM-D, a new vehicle being\ndeveloped.\ntail, giving low drag (two wings instead of three) and especially easy control during high-\naltitude flights. Tail retraction at landing is achieved by use of a semi-rigid hinge.\nThe weight of SAM-C and the need for operation on rough ground dictate the use of a cata-\npult and recovery nets. Because of a fineness ratio of 10, SAM-C can be operated in strong\nwinds (15 m/s) Technical specifications are given in Table 4.1.\n19","Table 4.1. Technical characteristics of SAM aircraft\nSAM-B\nSAM-C\nSAM-D\n(Circular wing)\n(Classic airplane:\n(Stabilizer in front\nreversed dihedral)\nof delta wing)\nPayload\n0.6 kg\n1.8 kg\n0.8 kg\nTotal weight\n3.5 kg\n7.5 kg\n5.2 kg\nMinimum speed\n5 m/s\n10 m/s\n9 m/s\nCruise speed\n15 m/s\n25 m/s\n30 m/s\nInitial climb rate\n4 m/s\n5 m/s\n7 m/s\nOperational ceiling\n2000 m\n4000 m\n5000 m\nEndurance at sea level\n15 min\n1 h\n20 min\nWing span\n1.20 m\n3.15 m\n1.40 m\nWing area\n0.95 m²\n1 m²\n1.75 m²\nAir foil\nNACA 4415\nNACA 4415\nEngine (diesel)\n10 cm³\n1.5 HP at\n12000 rpm\nPropeller\n28 cm X 18 cm\nFuel\nMethanol +\nnitromethane + oil\nFigure 4.3. SAM-C taking off. Its weight (8 kg) dictates the use of a catapult.\n20","Modulation\nSensors\nConverters\n(Standard IRIG)\nF\nChannel\nP\nE\n70 kHz\nF\n1500-3000 Hz\nAntenna\nFM\nR\nMixing\nChannel\nTransmitter\nT\nAmplifier\nC\n403 MHz\n40 kHz\nv750-3000 Hz\nF\nR\nChannel\nU\nA\n22 kHz\n750-3000 Hz\nF\nFigure 4.4. Block diagram of telemetry.\nAntenna\nReceiver\nFilters\nF\nF\nF\nA/D\nConverters\nBCD\nBCD\nBCD\nInterfacing\nProcessing\nPlotting\nPrinter\nUnit\nBoard\nRecorder\nFigure 4.5. Block diagram of\ndata acquisition.\nRemote Control\n4.2.3\nDigital remote control uses a 250-mW transmitter with a center frequency at 436\nMHz and a bandwidth of 50 kHz. This device controls the engine, the airbrakes, the aile-\nrons, and the gas-sampling system.\n4.2.4\nTelemetry\nFigures 4. 4 and 4.5 are block diagrams of the telemetry and data acquisition.\nPressure, temperature, and humidity are measured with a vibrating wire sensor, thermistor,\nand hygristor (Fig. 4.6). Their characteristics are given in Table 4.2. Temperature and\n21","Time (s)\n0\n1\n2\n3\nAQ\nAQ\nAQ\nAQ\n1\n2\n3\n4\nFigure 4.6. Aircraft instrumentation.\nFigure 4.7. Data processing sequence:\nThe picture shows the pressure sensor,\nAQ) data acquisition, 1) median compu-\nthe micropump, two filters for gas sam-\ntation, 2) transfer function (fre-\npling, and the telemetry equipment.\nquency/parameter), , 3) recording of\nmedian value, 4) plotting on 9872 A.\nTable 4.2. Characteristics of PTU sensors\nSensors\nMeasurement Range\nResolution\nPrecision\nPressure\n150 mb\n7 Hz/mb\n+0.1 mb\n(vibrating wire)\nbetween\n1050 and 500 mb\nTemperature\n(thermistor --\n-15°C to + 40°C\n20 Hz/o\n+0.2°C\nML 419)\nHumidity\n(hygristor --\n20% to 100%\n20 Hz/%\n+5%\nML 476)\nhumidity sensors are protected against solar radiation, and the shielding device offers\nappropriate ventilation during the flights.\nThe transmitter has a carrier frequency of 403 MHz, an HF power of 60 mW, a\nbandwidth of 100 kHz, and IRIG subcarriers of 22 kHz (humidity), 40 kHz (temperature), and\n70 kHz (pressure). It is thus possible to get real-time profiles of temperature and humid-\nity versus pressure or approximate altitude, assuming that the pressure gradient is con-\nstant within the flight range.\n4.2.5\nData-Processing\nThe data-processing system consists of a Hewlett Packard HP 9825 minicomputer\n(24 K memories), a plotter, and a 9866B thermal line printer (Fig. 4.5). The system allows\nfor plotting one value every 3 s, corresponding to three measurements (acquisition rate =\n1 Hz). The computer eliminates extreme values, retains the center value, converts into\nmeteorological data, plots temperature versus pressure, and stores the data on a cassette\nunit. (Figure 4.7 is a time diagram of the computer operations.)\n22","940\n950\n960\n970\n980\n990\n1000\n1010\nFigure 4.8. Example of temperature-versus -\npressure plot on new emagram '900'\ndesigned for the boundary layer. (Plot\n1020\nshown is redrawn from original real-time\nplot. ) Taken at Porcheville 6 July 1979\nat 0600 by SAM C06.\n1030\n+30\n+20\n+10\n0\nTemperature (°C)\nReal-time - processing\n4.2.5.1\nReal-time plotting of temperature versus pressure is possible on any emagram. A\nspecially designed one (Fig. 4.8) for low atmosphere is characterized by a linear pressure\nscale between 1050 and 900 mb and isotherms perpendicular to isobars.\nDelayed data processing (20 min)\n4.2.5.2\nStored data can be further processed. The raw data extraction program prints\ntime, pressure, temperature, humidity, height (through Laplace equation), and altitude.\nThe correction program eliminates the wrong values from the first shorter set. The final\nprocessing program prints time, pressure, temperature, humidity, height, altitude, dew\npoint, adiabatic wet-bulb temperature. Final data are also recorded on cassettes.\nPlottings\n4.2.5.3\nProcessed data can be plotted on emagrams as temperature, dew-point temperature,\nand adiabatic wet-bulb temperature versus pressure (Figs. 4.9 and 4.10). Certain flight\nparameters, such as pressure or vertical speed versus time or height (Fig. 4.11), can also\nbe plotted.\n23","800\n25°\n20°\n850\n15°\n900\nOw\nTd\nT\n10°\n950\n5°\n1000\n0°\n1050\n+5°\n+10°\n+15°\n+20°\n+25°\nTemperature (°C)\nFigure 4.9. Example of T, Td and OW plots during ascent. (Plot is redrawn from\nreal-time plot, which shows points for both ascent and descent. ) Data were taken at\nChateauroux 23 July 1979 at 0500 by SAM Bll.\n4.3\nSUMMARY OF PREVIOUS USES\n4.3.1\nMount Etna\nA remotely piloted SAM-C was successfully used in June 1978 on Mount Etna, a\nvolcano in Sicily, in cooperation with H. Tazieff's team of volcanologists. The experiment\nhad two objectives:\n(1) To study the thermal environment of the volcano to assess the modification of\nthe vertical profile of temperature by the mountain (and the volcano).\n(2) To sample the gases in the plume of the volcano to determine chemical\nproperties and prove the feasibility of the SAM method for physical and chemical\nresearch of volcano plumes.\n4.3.2\nChateauroux\nSAM-B was employed at Chateauroux during July 1978 to monitor the inversion\nlayer early in the morning and give accurate knowledge of the time of thermal plume forma-\ntion, so that take-off schedules for the Glider World Championship held there could be\n24","800\n600\nRH (%)\n0\n50\n100\n790\n400\n800\nTd\n810\n200\n820\nRH\n830\n0\n20\n25\n30\n-5\n0\n5\n10\n15\nTemperature (°C)\nFigure 4. 10. Example of T, Id, and RH plots during ascent as a function of\nheight. (Plot shown is redrawn from real-time plot, which shows points for\nboth ascent and descent with different measurements indicated in different\ncolors. ) Taken at Boulder 28 August 1979 at 0930.\n750\n800\nFigure 4 11. Pressure versus time plot\nrecorded during flight\n850\n750\n1000\n0\n250\n500\nTime (s)\nfixed. Thirty-eight soundings were performed during 14 days, with time intervals varying\nfrom 1 h (around 0500 UT) to 20 min (around 1000 UT).\nPlant Pollution Studies\n4.3.3\nDuring July 1979, SAM-C was used with a new sampling device consisting of 1.5-l\nglass containers with an initial internal pressure of 1 mb. These containers were opened\nby a remote control system and were filled in approximately 5 S, then closed again. Anal-\nyses were conducted on the site immediately after each flight with an ultraviolet fluores-\ncence method (SO).\n25","5. COMPARISON OF AIRCRAFT AND BAO TOWER MEASUREMENTS\nD. H. Lenschow and B. B. Stankov\nNational Center for Atmospheric Research\nBoulder, Colorado, U.S.A.\n5.1\nINTRODUCTION\nFrom 17 to 28 April 1978, a site evaluation study was conducted in the vicinity\nof the Boulder Atmospheric Observatory (BAO) tower to help determine the degree to which\nthe tower measurements are representative of the surrounding area. This was the initial\nfield research program involving the BAO tower. An NCAR Queen Air aircraft was used to\nobtain measurements along horizontal flight paths centered at the tower for comparison\nwith concurrent tower measurements.\nIntercomparisons of tower and aircraft measurements are carried out periodically\nby NCAR primarily to calibrate and check aircraft measurements of temperature, pressure,\nand humidity. This is particularly important for experiments involving several instrument\nplatforms probing the same phenomena. Biter and Wade (1975) describe the techniques and\nequipment used for such an intercomparison during the National Hail Research Experiment\n(NHRE) and present some examples of the results. Their accuracy tolerances were +0.5 K\nfor air and dewpoint temperature, and +1 mb for static pressure. Measurements of turbu-\nlence quantities such as variances and fluxes, however, are not routinely compared.\nThe region surrounding the tower is gently rolling terrain used for grazing,\ndryland and irrigated farming, and suburban living. As shown in Fig. 5.1, the general\nterrain slope is toward the northeast, although the local slope near the tower is toward\nthe north. As pointed out by Lenschow et al. (1979), even very slight terrain variations\ncan cause large variations in the overlying boundary layer, particularly at night and\nduring the initial development of the daytime convective mixed layer. In addition to\nlocal terrain variations, the foothills of the Rocky Mountains rise to more than 600 m\nabove the BAO site within 25 km west of the tower. About 25 km farther west, the Front\nRange towers about 2500 m above the BAO site. Therefore, we expect that, under certain\nconditions depending upon the height above the ground, the tower measurements will not\nrepresent the surrounding area.\n5.2\nEXPERIMENTAL DETAILS\nThe BAO tower was instrumented for measurements of wind velocity components,\ntemperature, and humidity at heights of 10, 20, 50, 100, 150, 200, 250, and 300 m above\nthe ground. Details of the tower, its instrumentations, and the data acquisition and\nrecording are discussed by Kaimal (1978). Twenty-minute-block averages of winds and\ntemperature, recorded at a sampling rate of 10 Hz, and standard deviations from the 20-min\nmeans were calculated and compared with the aircraft measurements.\nThe NCAR Queen Air, shown in Fig. 5.2, is a light twin-engine aircraft that can\nbe equipped for a variety of research programs (Burris et al., 1973). The aircraft meas-\nurements in the site evaluation study included the three wind components, air and surface\ntemperature, and humidity. Air motion measurements were calculated from the airplane\nvelocity and attitude angles, measured with an inertial navigation system (INS), and the\nair velocity with respect to the airplane was obtained from sensors at the tip of the nose\nboom. A Rosemount platinum-resistance-wire thermometer, with a wire diameter of 25 um, is\nalso mounted near the tip of the nose boom. The measured total air temperature is then\ncorrected for heating caused by the rapid air flow. Further details on the air motion\nsensing system are presented by Lenschow et al. (1978), and on airplane temperature and\nvelocity measurements by Lenschow (1972).\n26","6000\n4800\n40.2\nLongmont\n5200\n5400\n5000\n5600\nin\n5800\n6000\n40.1\nBAO\n5200\nTower\nErie\nBoulder\n40.0\n5000\n5200\n5400\n5200\n5600\n5800\n39.9\n6000\n104.8\n104.7\n105.0\n104.9\n105.1\n105.3\n105.2\nFigure 5.1. The region surrounding the Boulder Atmospheric Observatory tower\nand the research aircraft flight path (----).\nThe aircraft data were recorded at 20 Hz and divided into segments of 4096 sam-\nples. At an average aircraft speed of 70 m/s, this is equivalent to a length of 14.3 km.\nFor comparison with the tower data, at a wind speed of 10 m/s, the equivalent averaging\ndistance for a 20-min time series is 12 km. Before standard deviations were calculated,\nthe mean and a Least-squares linear trend were removed from each segment.\nBecause of flight restrictions over the suburban tower surroundings, the minimum\naircraft flight altitude is 150 m above the ground. Therefore, intercomparison measure-\nments were made only at the 150- and 300-m levels of the tower. The aircraft flight path\nis shown in Fig. 5.1. The aircraft was flown at a constant height above the ground,\nmeasured by a radar altimeter. Altogether, 13 flights totaling 28 h were conducted. Here\nwe present a comparison of tower and aircraft measurements during Flight 6, from 1551 to\n1751 MST on 21 April 1978.\nA weak cold front had passed through the area several hours earlier and the wind\nwas quite steady from the northwest. The sky was partly covered with cumulus clouds, with\nno precipitation. Solar heating was sufficient to generate a convective mixed layer well\nabove the airplane flight path.\nThe flight path used on this day was a 30-km-long I-shaped pattern, centered at\nthe tower, as shown in Fig. 5.1. This pattern, which took less than 15 min to complete,\nwas flown continuously for eight cycles, all at 150 m above the ground, except for the\nlast cycle, which was at 300 m. On most of the other days, an X-shaped flight path was\n27","Figure 5.2. NCAR Queen Air research aircraft.\nchosen to allow comparisons of aircraft and tower measurements at locations approximately\nuniformly surrounding the tower. However, it took 30 min to complete this pattern and,\nfurthermore, on two of the four traverses by the tower, the airplane turned at the tower.\nSince turns can have an adverse effect on the accuracy of spatially averaged airplane wind\nmeasurements, reliable values centered at the tower were obtained for only half of the\nflight legs past the tower.\n5.3\nTOWER-AIRCRAFT INTERCOMPARISON\nTables 5.1-5.3 summarize the comparisons between the airplane and tower measure-\nments. Since the length of an entire flight leg is only about 30 km, the north (Table\n5.2) and south (Table 5.3) segments each overlap the center segment by about 6 km.\nThe mean values of tower and airplane measurements of horizontal wind components\nand temperature agree well with each other. The average difference of the velocity compo-\nnents is 0.6 m/s, with no significant difference between the segments by the tower and the\nother segments. Similarly, the average temperature difference is only about 0.4 K. Thus,\nhorizontal variations were not large enough during this period to cause significant errors\nin the mean.\nThe standard deviations of the aircraft horizontal wind components are consist-\nently somewhat larger and more variable than the tower measurements, particularly for the\nsegments away from the tower. Although we do not know the reason for this, there are two\npossibilities:\n(1) The wind may be affected somewhat by the terrain. On the north leg, we observed\nthat u consistently reached a maximum in the middle of the segment, then decreased at\nthe end of the leg. It is difficult to determine, however, even the scale of terrain\nvariation that might cause such a perturbation.\n(2) The airplane measurements may include contributions from longitudinal rolls\n(LeMone, 1973) since the airplane flight path is approximately perpendicular to the\nwind. If the rolls are aligned approximately with the wind, the tower may not pass\nthrough a complete cycle during the 20-min measurement period.\nTower and airplane measurements of the standard deviations of vertical velocity\nand temperature show good agreement with each other. This may be the result of relatively\nless contribution to the standard deviations by terrain-induced variations and longitudi-\nnal rolls than by the horizontal velocity components.\n28","0.14\n.21\n.07\n0.24\n0.32\n0.16\n0.21\n0.17\no\nComparison of airplane (subscript A) and tower (subscript T) measurements of velocity\n.20\n.02\n0.18\n0.23\n0.27\n0.19\n0.19\n0.21\n0\no\n0.67\n305.3\n304.5\n304.1\n305.1\n306.0\n305.3\n305.1\nT\n0\nK\n0.63\ncomponents and temperature for the flight segments centered at the tower\n304.6\n304.2\n304.0\n304.5\n303.7\n305.3\n305.1\nA\n0\nWT\n.70\n.71\n.85\n.90\n0.17\n1.08\n1.07\n1.00\nO.\nThe horizontal velocity components are oriented towards the east (U) and north (V).\n0.78\n0.70\n.85\n.93\n0.18\nWA\n1.19\n1.00\n1.03\nO\n1.34\n0.36\nVT\n0.93\n0.93\n1.35\n1.79\n1.33\n1.69\nO.\n1.42\n0.29\n1.16\n1.04\n1.61\nVA\n1.66\n1.72\n1.31\nN is the number of 14-km flight segments during each time period.\no\n-5.8\n-7.1\n-5.0\n-5.9\n0.9\n-7.0\n-5.5\n-5.3\nT\nV\n-4.4\n-5.0\n0.7\n-5.7\n-5.8\n-5.0\n-5.3\n-4.0\nA\nV\nm/s\n1.06\n1.36\n1.23\n0.21\nUT\n1.58\n1.15\n1.15\n1.05\no\n1.34\n0.19\nUA\n1.64\n1.63\n1.20\n1.07\n1.42\n1.38\no\n10.4\n8.8\n7.0\n9.9\n1.7\n10.8\n12.0\n10.4\nT\nU\n10.3\n1.7\n10.0\n8.7\n8.0\n2\n11.5\n12.1\n11.5\nA\nU\n1\nTable 5.1\n3\n2\n2\nN\n3\n3\n3\n150\n150\n300\n150\n150\n150\nM\nh\nAverage\nof time\nCenter\nperiod\n1701\n1721\n1741\n1601\n1621\n1641\no\nMST\n1\n2","0.24\n0.32\n0.16\n0.21\n0.17\n0.14\n0.21\n0.07\nTable 5.2. Comparison of airplane (subscript A) and tower (subscript T) measurements of velocity components\no\n0.22\n0.22\n0.20\n0.20\n0.23\n0,26\n0.22\n0,02\nto\no\n0.67\n306.0\n305.3\n305.3\nK\n305.1\n304.5\n304.1\n305.1\nT\n0\n0.62\n305.9\n305.7\n305.4\n305.0\n304.5\n304,4\n305.2\nA\n0\nWT\n1.08\n1.07\n1.00\n0.70\n0.71\n0,85\n0.90\n0.17\nO\nWA\nand temperature for the flight segments centered north of tower\n1.11\n1.05\n1.04\n0.83\n0.72\n0.87\n0.94\n0.15\nO\no VT\n1.79\n1.33\n1.69\n0.93\n0.93\n1.35\n1.34\n0.36\nVA\n1.60\n1.54\n1.55\n1.47\n1.82\n1.73\n1.62\n0,13\no\n-7.0\n-5.4\n-5.3\n-5.8\n-7.1\n-5,0\n-5.9\n0.9\nT\nV\n-3.8\n-5.0\n-4.5\n-5.7\n-6.5\n-5.5\n-5.2\n0.9\nA\nV\nm/s\nUT\n1.58\n1.15\n1.15\n1.05\n1.06\n1.36\n1.23\n0.21\no\nUA\n1.49\n1.57\n1.27\n2.20\n2.46\n1.94\n1.82\n0.46\no\n10.8\n12.0\n10.4\n10.4\n8.8\n7.0\n9.9\n1.7\nT\nU\n11.4\n12.8\n12.4\n10.4\n8.1\n7.7\n10.5\n2.2\nA\nU\nN\n3\n3\n3\n3\n2\n2\n150\n150\n150\n150\n150\n300\nM\nh\nof time\nAverage\nCenter\nperiod\n1601\n1621\n1641\n1701\n1721\n1741\nMST\no","Comparison of airplane (subscript A) and tower (subscript T) measurements of velocity components\n0.24\n0.32\n0.16\n0.21\n0.17\n0.14\n0.21\n0.07\no\n0A\n0.20\n0.19\n0.17\n0.18\n0.20\n0.02\n0.23\n0.22\no\nK\n0.67\n306.0\n305.3\n305.3\n304.7\n305.1\n305.1\n304.5\nT\n0\n0.75\n305.7\n305.0\n304.5\n304.1\n303.9\n303.7\n304.5\nA\n0\n1.00\n0.70\n0.71\n0.85\n0.90\n0.17\nWT\n1.08\n1.07\no\nand temperature for the flight segments centered south of tower\nWA\n0.90\n0.85\n1.48\n1.12\n0.23\n1.22\n1.08\n1.19\no\n0.93\n0.93\n1.35\n1.34\n0.36\nVT\n1.79\n1.33\n1.69\no\n1.76\n1.54\n0.32\nVA\n1.60\n1.80\n1.79\n1.25\n1.05\no\n-5.8\n-7.1\n-5.0\n-5.9\n0.9\n-7.0\n-5.4\n-5.3\nT\nV\n-4.0\n0.8\n-5.8\n-5.5\n-5.8\n-5.4\n-4.0\n-5.1\nA\nm/s\nV\nUT\n1.58\n1.15\n1.15\n1.05\n1.06\n1.36\n1.23\n0.21\no\n1.93\n1.71\n1.35\n1.25\n1.20\n2.11\n1.59\n0.40\nUA\no\n7.0\n9.9\n1.7\n12.0\n10.4\n10.4\n8.8\n10.8\nT\nU\n10.0\n2.8\n11.5\n9.4\n7.3\n7.7\n11.1\n12.7\nA\nU\n3\n2\n2\n3\n3\n3\nN\n150\n150\n300\nTable 5.3.\n150\n150\n150\nM\nh\nAverage\nof time\nCenter\nperiod\no\n1701\n1601\n1621\n1641\n1721\n1741\nMST","5.4\nSUMMARY\nThe excellent agreement found in this initial comparison of mean values and\nstandard deviations of velocity and temperature measured concurrently by the BAO tower and\nan aircraft is very encouraging. We can make useful comparisons of many other items of\ninterest, such as covariances, time changes at the tower versus horizontal gradients from\nthe aircraft, and spectral and cospectral quantities. These comparisons could help to\ndetermine the degree to which the tower measurements are affected by terrain inhomogenei-\nties. Varying degrees of horizontal inhomogeneity in the boundary layer might be observed\nwith different synoptic situations and at different times of day. Comparison of airplane\nand tower spectra may also be useful in determining the validity of Taylor's hypothesis,\ni.e. , that time and space averages are interchangeable.\n5.5\nREFERENCES\nBiter, C. J., and C. G. Wade (1975) Field calibration and intercomparison of aircraft\nmeteorological measurements. Preprint Vol. 1, NHRE Symposium/ Workshop on Hail,\nSeptember 1975, VIII.A.63.1-63.21 (Available from NCAR, P.O. Box 3000, Boulder, CO\n80307.)\nBurris, R. H., J. C. Covington, and M. N. Zrubek (1973): Beechcraft Queen Air aircraft.\nAtmos. Technol. 1:25-27.\nKaimal, J. C. (1978): NOAA instrumentation at the Boulder Atmospheric Observatory.\nPrepr. 4th Symp. on Meteorol. Obs. and Instrum., 10-14 - April 1978, Denver, Colo.,\nAmerican Meteorological Society, Boston, Mass., pp. 35-40.\nLeMone, M. A. (1973): The structure and dynamics of horizontal roll vortices in the\nplanetary boundary layer. J. Atmos. Sci. 30:1077-1091.\nLenschow, D. H. (1972): The measurement of air velocity and temperature using the NCAR\nBuffalo aircraft measuring system. NCAR-TN/EDD-74. National Center for Atmospheric\nResearch, Boulder, Colo., 39 pp.\nLenschow, D. H., C. A. Cullian, R. B. Friesen, and E. N. Brown (1978): The status of air\nmotion measurements on NCAR aircraft. Prepr. 4th Symp. on Meteorol. Obs. and In-\nstrum., 10-14 April 1978, Denver, Colo., American Meteorological Society, Boston,\nMass., , pp. 433-438.\nLenschow, D. H., B. B. Stankov, and L. Mahrt (1979): The rapid morning boundary layer\ntransition. J. Atmos. Sci. 36:2108-2124.\n32","6. TETHERED AERODYNAMICALLY LIFTING ANEMOMETER (TALA)*\nCharles F. Woodhouse\nApproach Fish, Inc.\nClifton Forge, Virginia, U.S.A.\n6.1\nINTRODUCTION\nVariable altitude anemometry is a new method which is beginning to find applica-\ntion in low -level wind measurement. The principle is simple. Since wind-tunnel veloc-\nities are used to calibrate the lift and drag of an airfoil, if the characteristics of a\nfree-flying airfoil are known then the velocity of the wind can be determined. The air-\nfoil sensor or kite described here is stable in naturally turbulent winds to 50 m/s (Fig.\n6.1).\nFigure 6.1. Patented sled airfoil is\nstable to 40 m/s. The tether line\nforce is practically that of a theo-\nretical flat plate:\n1.967\n= pv 2\n.\nMEASUREMENT OF WIND SPEED\n6.2\nThe tension on the tether line produced by lift and drag forces acting on the\nkite provides a measure of wind speed at kite level. The force on a flat plate is\nq = PV 2 2\n(6.1)\n,\nwhere q = force, p = density, and V = speed; q is quite close to the force on the sensor\n9k as determined by wind tunnel calibration:\nIk = p V 1.967 2\n(6.2)\n.\n*U.S. Pat. numbers 4,058,010 and 4,152,933.\n33","30\n25\n20\nFigure 6.2. Original calibration of air-\n15\nfoil at NASA-Langley with correlation\nat NBS of electronic equipment built to\n10\nLangley formula. = NASA-Langley data\npoints (calibration 5 April 1976; corre-\nlation coefficient .999).\n= National\n5\nBureau of Standards data points (cali-\nbration 17 March 1978; correlation co-\nefficient .997).\n5\n10\n15\n20\n25\n30\nWind tunnel true (m/s)\nThe force 9k is measured directly by a strain gauge attached to the end of the\ntether line. Correlation coefficients as determined in the large NASA-Langley and the NBS\nwind tunnels are 0.999 and 0.997 respectively (Fig. 6.2).\nCar-tow calibration in still dawn air (Fig. 6.3) at 175 m altitude shows a wind\ndrift between east and west runs. Car speed was calibrated by radar.\nCalibration in natural winds against cup or propeller anemometers is difficult\nbecause the empirical and varying turbulence correction equations of these instruments\n(McMichael and Klebanoff, 1975) are in the 1% to 2% range (Baker et al., 1979). Pre-\nvious calibration against the BAO sonic anemometers indicates accuracies within 0.65%\nWe will test this agreement more accurately during the BLIE intercomparison.\nCatenary drag and the relationship between catenary cable curvature and height\nhave been extensively studied. The present cable used is only 250 microns in diameter\nwith a weight of 115 g/km. Computer analysis of the dynamics of this line (Shieh and\nFrost, 1979) has shown that for a cable of that type the maximum effect of catenary drag\non the measured tension at the ground is five orders of magnitude smaller than the\ntension produced by the airfoil itself.\n6.3\nMEASUREMENT OF ALTITUDE\nThe kite altitude is a function of line length, corrected for catenary sag and\nthe observed vertical angle to the kite. The following empirical relationship is used:\nZ = 0.9 sino (0.3n - 2.2 X 10 5 n 2 )\n(6.3)\nwhere Z is the kite altitude, is the observed sensor vertical angle and n is the reel\ncount (Fig. 6.4) The 0.9% correction factor in (6.3) compensates for the effect of\ncatenary curvature (Shieh and Frost, 1979). This correction is small because of the low\nweight and low drag of the line. The equation used for estimating decrease in reel diam-\neter as line is payed out is found to be accurate to 1%.\nVertical angle 0 can be determined from a hand-held clinometer. In the elec-\ntronic model, altitude is computed automatically from measurements of the string angle at\n34","20\nAltitude 310m\nAltitude 175m\nEast\nX\nEast\nX\nX\nX West\nX West\n15\nX\n10\n5\n20\n5\n10\n15\n15\n5\n10\nCar Velocity (ms-1)\nFigure 6.3. Car tow calibration at 175 m shows slight wind drift between\neast and west runs.\nthe base and of the line payout. A catenary correction control allows compensation for\ndifferences between visual angle and string angle, for different amounts of line length.\nThe kite flies at a constant angle of attack to its apparent wind. Wind-tunnel\ndata show a tether repose angle of 53° at 5 m/s rising to 57° at 20 m/s. Car-tow data\n(Fig. 6.5) illustrate the constant flight altitude at speeds of 5 m/s to 20 m/s.\nMEASUREMENT OF WIND DIRECTION\n6.4\nA simple potentiometer device attached to the end of the tether line measures\nazimuth wind direction. The potentiometer readings are referenced to true north. A\npronounced lateral bend in the line will introduce errors in the wind direction reading,\nbut this can be corrected by entering into the data acquisition system an initial visual\nreading of the direction of the upper section of the tether line. In order to make this\nmeasurement it will be necessary to move to either the left or right of the tether point\nwith a precision magnetic compass.\nCHARACTERISTICS OF THE KITE\n6.5\nThe airfoil weighs 16 g and has a surface area of 1500 cm2 It acts, when under\ntension in flight, much like a large electrostatic loudspeaker cone. Because of the low\nweight and large surface, its compliance is high. The tether, or force transmission line,\nis of inelastic Kevlar (DuPont) with a modulus of elasticity in the range of steel. Thus,\nthe frequency response of the sensor is high. Field measurements from the sensor flying\nat 100- to 200-m altitude show a response of at least 10 Hz in a 10 m/s wind field.\nThe free-flying sensor orients directly and at constant angle of attack to its\napparent wind. Thus its altitude of flight at specific line lengths is a direct function\nof the vertical component of the apparent wind vector. Similarly, horizontal position\nchanges are a function of the lateral component. A measurement of the lateral and verti-\ncal turbulence may be obtained to altitudes of 300 m.\n35","1.0\n0,9\nV. K = 10 m/s\n0.8\nL 360 m\n0.7\n30.5\n0.6\n0.5\nApproximately 0.1%\n0.4\n0.3\nP 0.14\n0.2\nP 0.0\n0.1\n0.0\n0.1\n0.2\n0.3\n0.4\n0.5\n0.6\n0.7\n0.8\n0.9\n1.0\nX/L\nFigure 6.4. Analysis (Shieh and Frost, 1979) showing 0.1% effect\nof varying wind field on altitude where V = wind speed at sensor\nlevel; L = line length; = sensor elevation angle; Z = height;\nX = distance; p = power law exponent.\nThe kite will fly stably at wind speeds as low as 3 m/s To lift the kite under\nsuch conditions, an ancillary balloon inflated with helium to a specific circumference may\nbe attached with surgical silk, or mercerized cotton thread to the sensor. The surgical\nsilk breaks away at wind speeds of 4 m/s.\nAt wind speeds of less than 3 m/s the helium- - filled balloon lifts the sensor\nthrough calm inversions to upper altitude winds. The angle of the restraining tether is a\nfunction of lift/drag, and the altitude is a function of line length out and tether repose\nangle. As the sensor is lifted through the inversion into winds greater than 4 m/s the\nlifting balloon breaks away from the now flying sensor.\n6.6\nEQUIPMENT OUTPUT CHARACTERISTICS\nWind speed:\nThe line tension strain gauge outputs are internally calculated to give 400\nmV/m/s; thus, 10 V = 25 m/s.\nDirection:\nTether line direction is calculated from a reference centerline voltage of\n5.0 V at + 36° per volt.\n36","300\n250\nReel Count 2340\n200\nReel Count 1050\n150\nReel Count 570\n100\nReel Count 300\n50\n15\n20\n5\n10\nVelocity (m/s)\nFigure 6.5. Altitude of sensor at increasing line length and speed, illustrating\nrelatively constant altitude of flight at velocities above 5 m/s.\nAltitude from 0 to 300 m is calculated from line length and catenary angle\nAltitude:\nat 33 mV/m; thus, 10 V = 300 m.\nAnalog oscillation-free outputs are sampled at 0.8 Hz by a portable digital\nDigital:\nrecorder. Mean standard deviation and minimum and maximum values are calcu-\nlated for each parameter each minute and stored on a cassette tape for\nlater data reduction. The data output is RS232-compatible at 300 baud.\n6.7\nREFERENCES\nBaker, R. W., R. L. Whitney, and E. W. Hewson (1979): A low level wind measurement tech-\nnique for wind turbine generator siting. Wind Eng. 3:107-115.\nBaker, R. W., , R. L. Whitney, and E. W. Hewson (1979): Wind profile measurements using a\ntethered kite anemometer. Am. Wind Energy Conf., 16-18 April 1979, San Francisco,\nCalif. , American Wind Energy Association, Washington, D.C.\nDelaurier, J. D. (1972): A stability analysis of cable-body systems totally immersed in a\nfluid stream. NASA CR-2021, Stanford Univ., , Dept. of Aeronautics and Astronautics,\nStanford, Calif., , 93 pp.\nMcMichael, J. M., and P. A. Klebanoff (1975): The dynamic response of helicoid anemometers.\nNBSIR 75-772, U.S. Dept. of Commerce, National Bureau of Standards, Washington, D.C. ,\n54 pp.\nShieh, C. F., , and W. Frost (1980): Tether analysis for a kite anemometer. Conf.\non Wind Characteristics and Wind Energy Siting, 19-21 June 1979, Portland,\nOre. Pacific Northwest Laboratory, Richland, Washington.\n37","7. REMOTE ACOUSTIC ELECTRONIC SOUNDING (RACES)\nP. Ravussin\nFederal Institute of Technology\nLausanne, Switzerland\n7.1\nINTRODUCTION\nThe Remote Acoustic Electronic Sounding system (RACES) can measure in the lower\nlayer of the atmosphere the vertical profile of the three-dimensional wind vector, the\nvertical profile of temperature, and the vertical profile of humidity. The version de-\nscribed here measures only the vertical profiles of vertical wind and temperature. As the\nmeasurements are made at the same time and in the same sampling volume, the system can\ncalculate in time the vertical profile of the thermal coefficient of turbulent diffusivity\nKh,\nTHE\n(7.1)\nwhere T is the aleatory variable of the temperature, and T=T+T', u3 is the aleatory var-\niable of the vertical component of the wind, and u3 = u3 + . T and are the statistical\naverages, defined in terms of probability density functions p(T) and p(u3) :\n=\n(7.2)\nand\nu3=\n(7.3)\nSince the RACES system measures time series, the ergodic assumption of the stationarity of\nthe measured phenomenon must be made, to replace the statistical averages by time averages.\nThe averaging time is a critical parameter which depends on atmospheric conditions and\ntopography.\n7.2\nOPERATION\nThe RACES system is based on the physical properties of transmission and diffu-\nsion of sound in the atmosphere. Thus the basis of the instrument is an electro-acoustic\ndevice which transmits vertically in the atmosphere.\n7.2.1\nSound Transmitter\nThe sound transmitter (Fig. 7.1) contains an oscillator, which produces a sinus-\noidal electric signal at a very stable frequency f = 1600 Hz, Af/f < 10-6 The signal is\ntransmitted through a switch (which is electronically operated) to a power amplifier and\nthen to the electro-acoustic transducer. There the electric signal is transformed to an\nacoustic wave. The efficiency of the transducer is low:\n20% ,\n(7.4)\n38","pulse of sound\nacoustic\nenclosure\npower\namplifier switch oscillator\ntransducer\nparabolic\nFigure 7.1. Diagram of sound\nreflector\ntransmitter.\nwhere Ps = acoustic power, and Pe = electric power.\n(7.5)\nwhere u is the instantaneous voltage applied to the transducer and Z is the electrical\nimpedance of the transducer at the oscillator frequency (1,600 Hz). . The relation between\nthe effective (\"eff) and peak (up) values is given for a sinusoidal signal by\n(7.6)\nIn the low-power version used here Pe = 30 W, and the acoustic power is only 6 W.\nSampling Volume\n7.2.2\nThe sampling probe is the sound pulse itself. The sizes of the sampling volume\nare identical to the sizes of the sound pulse. The pulse duration is tp==00 = ms. The\nlength of the sampling volume is given by\n(7.7)\nd=cs t P\n.\nC is the speed of sound in the air, and varies slightly with the temperature according to\nS\nthe law\nC = 20.05 VT ,\n(7.8)\nwhere T = temperature (K). At 20°C, l = 17 m.\nThe acoustic antenna is circular, which gives the pulse of sound a cylindrical\nform whose diameter varies with the altitude according to the law of diffraction of a\ncircular opening.\n0=1.22 1/2 A\n(7.9)\nwhere 1 = wavelength of the sound (m), and d = diameter of the antenna.\n39","I/Io\nP/P.\nd\n1\n1\n0.8\npulse of\n08\nsound\n05\n0.5\nX3\n20\n0\n1\n0.5\n0/0.\nFigure 7.2. Sound propagation from\nFigure 7.3. Acoustic intensity and\nacoustic antenna.\npower as a function of angle.\nl = C H I C S\n(7.10)\nFor the 1600-Hz signal at 20°C,\nl = 0.21 m.\nFor the present low-power version, the diameter of the antenna is 1.31 m. It is therefore\npossible to calculate at which altitude the diameter and the length of the pulse of sound\nwill have the same value (Fig. 7.2):\nsin(1.22 44 m .\n=\n(7.11)\nThe intensity of the sound is, however, not constant in the sampling volume. It varies\naccording to the law\n0) 2\nTHE k sin k sin 0\n(7.12)\nwhere I = intensity at the center, J1 = first-order Bessel function, k = wave number =\n2n/A.\nFigure 7.3 shows that 80% of the power is emitted in an angle\n0 111 0.5 00\n.\nFor the RACES system, the length and the diameter of the sound pulse reach the same size at\nan altitude of ~90 m.\n40","Table 7.1 Corrections for relative humidity\n0% H\n100% H\nTemp.\n+0.23\n0°C\n-0.23\n+0.48\n-0.48\n10°C\n+0.93\n20°C\n-0.93\n+1.78\n30°C\n-1.78\n7.2.3\nTime Constant\nThe time constant in the RACES system is the time that the sound takes to propa-\ngate along a distance equal to the length of the sound pulse. This is obviously the time\nduration of the pulse (50 ms). The RACES system is therefore capable of measuring the in-\nstantaneous value of the spatial average of the parameters T and in the sampling volume.\n(7.13)\n(7.14)\ndV\n.\nMEASUREMENT OF THE TEMPERATURE PROFILE\n7.3\nThe speed of sound propagation in air is directly connected to the thermodynami-\ncal properties of the atmosphere. Because of this the RACES system measures directly the\nabsolute value of the temperature.\n7.3.1\nTheory\nThe speed of sound in the air depends solely on the temperature. This can be\ndeduced from the equation of the mechanics of fluids and the thermodynamic equations of\nthe adiabatic processes,\nC's - VAT = YRT u\n(7.15)\n,\nwhere Cs = speed of sound (m/s), y = ratio of the isobaric and isochoic specific heats,\nR = gas constant (J mole -1 K-1), H = molecular weight (mole , and T = absolute\ntemperature (K)\nIn a dry atmosphere the proportions of the main gases, Ar, N2, and O2, are\nconstant. In this case H is also constant. r does not vary with atmospheric pressure but\ndoes, very slightly, with temperature. However, the effect is negligible within a 10°C\ntemperature variation.\nEffect of the Air Moisture\n7.3.2\nUnfortunately the effect of the water vapor in the atmosphere is too strong to be\nnegligible, especially at high temperatures. Because this version of the RACES system does\nnot measure the vertical profile of humidity, the assumption of a constant 50% humidity\nprofile was made. As seen in Table 7.1, the influence of moisture decreases rapidly with\ntemperature. Table 7.1 gives the corrections for 100% and 0% relative humidity compared\nwith 50% relative humidity, at different temperatures.\n41","Cs = 330 m/s\npulse of sound\nC = 3.108 m/s\ngalvanic screen\nacoustic\nantennas\nUHF\nUHF\ntransmitting\nreceiving\nantennas\nantennas\narray\nFigure 7.4. Measurement of speed of sound propagation in the atmosphere.\n7.3.3\nEffect of the Vertical Wind\nThe measured speed of sound is the sum of the effective speed of the sound and\nthe vertical wind. Since the vertical wind is measured at the same time and in the same\nsampling volume, the computer can calculate this correction.\nC's = 20.05 VT + \"3.\n(7.16)\n7.3.4\nTemperature Measurement\nSince the speed of sound in the atmosphere depends mainly on the temperature,\nthe propagation speed of the sound pulse is directly measured with a CW Doppler radar.\nThe principle is illustrated in Fig. 7.4.\nThe wavelength of the radar must be exactly twice the wavelength of the sound\npulse (which varies with the temperature). In order to improve the range, a feedback\ndevice was patented which corrects the frequency of the CW Doppler radar according to the\nfrequency deviation of the return Doppler signal The circuit used in this version is a\nphase-locked - loop (PLL).\n42","At the point of equilibrium the Doppler signal must have the same frequency as\nthat of the sound pulse. Because of this, the same oscillator was used to produce the\nsound pulse and the reference signal for the feedback device. The relationship between the\nspeed of sound and the radar frequency is given by the Doppler-Fizeau law:\nAv CS\n(7.17)\n2v c\n,\nwhere Av = received Doppler-Fizeau frequency, V = frequency of the emitter, C's = speed of\nsound, and C = speed of the electromagnetic wave in the atmosphere. Since C is about 106\ntimes faster than Cs, the speed of sound measurements made by RACES are essentially instan-\ntaneous.\nThe time interval between the starting of the sound pulse and the time of measure-\nment gives the height of the measurement :\nt\n(7.18)\nh = C S dt\n.\nt\no\nThe system measures the ratio Av/V directly and is therefore independent of the\nphase effect introduced by the low-pass filter of the PLL.\nDescription of the System\n7.3.5\n7.3.5.1\nUHF transmitter\nThe UHF transmitter (Fig. 7.5) consists of a low-noise voltage-controlled oscil-\nlator (0.66 - 0.78 GHz ) followed by a power amplifier (1 W) and a four-Yagi, 26-element,\nwide-band antenna system. The opening angle of the antenna is about 20°.\n7.3.5.2\nUHF receiver\nThe UHF receiver consists of an array of five 26-element (15.5-dB Yagi) antennas,\nelectronically connected to the receiver. The purpose of the array is to compensate for\nthe effect of sound pulse displacement by the horizontal wind. The antennas are followed\nby a 54-dB low-noise UHF preamplifier and the Doppler mixer. For practical reasons only\none antenna was used for the Boulder comparisons.\n7.3.5.3 LF receiver and converter\nThe low-frequency receiver consists of a low-noise preamplifier, a gyrator\nfilter with adjustable Q factor from 0 to 1,000, a linear amplifier (0 - 40 dB), a log-\namplifier, and a signal shaper circuit. The signal is then transmitted to an adjustable\ndigital divider and to a UHF ratiometer with IEC-Bus interface The measurement time is\n12.5 ms. The measurement interval is 70 ms. This is because it takes about 35 ms to\ntransmit the information to the computer through the IEC-Bus. Consequently, the tempera-\nture is measured every 20 m only.\nMEASUREMENT OF THE VERTICAL WIND PROFILE\n7.4\n7.4.1\nTheory\nThe sound pulse propagating vertically in the atmosphere is diffused by the\nsmall 'inhomogeneities of the air. The coefficient of diffusion 00 depends on the angle of\ndiffusion of the thermal and wind turbulence according to the following expression:\n43","Receiving antenna\nacoustic antenna\ntransmitting antenna\narray\nLF\nVertical wind\nreceiver\nto vertical wind\nand\nmeasurement\nmeasurement\nconverter\nUHF\nlow noise\npower\nUHF\namplifier\namplifier\nLF power amplifier\nperiod\nTo mini-\nmeter\ncomputer\nmixer\nLF\nUHF\nlogic\nreceiver\noscillator\noscillator\nratio\nTo mini-\ncircuit\nand\nand\nmeter\ncomputer\nconverter\nPLL\nTemperature measurement\nFigure 7.5. Block diagram of RACES system.\n2\n2\n0° = 0.03 k 1/3 cos 2 0 N/Y C V cos 2 0 2 + 0.13 C T ) (sin pia -11/3\n(7.19)\n,\nwhere k = wave number of the sound, 0 = diffusion angle, Cv = wind turbulence parameter,\nV = wind speed, CT = thermal turbulence parameter, and T = temperature.\nThis law assumes that the wind turbulence and the thermal turbulence have a\nKolmogorov's spectrum. A small part of the sound is back-scattered and reaches the acous-\ntic antenna.\nFor 0 = TT ,\n22\n1/3\nT\nof=0.0039 k\nT2\nThe sound is back-scattered only by the thermal inhomogeneities of the atmosphere.\n44","Principle of the Wind Measurement\n7.4.2\nThe small-scale thermal inhomogeneities in the atmosphere have an average general\nmovement u3 in relation to the receiver's antenna. In this case, according to the Doppler\nlaw, the back-scattered sound that reaches the acoustic antennas has a frequency slightly\ndifferent from that of the emitting antenna.\nAf = 3\n(7.20)\n,\n2f C S\nwhere Af = Doppler frequency, f = frequency of the pulse of sound, u3 = vertical wind, and\nC's = speed of the sound in the atmosphere. Cs is measured by the temperature-measuring\npart of the RACES system.\nBecause the Fourier transform needs a stationary signal, the frequency measure-\nment of the received signal was not made with a spectrum analyzer. Instead the average\nperiod of the signal was directly measured with a zero-crossing technique. The average is\ntaken on 20 periods of the signal.\nLF Receiver and Converter\n7.4.3\nThe acoustic antenna signal is switched (a few milliseconds after the emission\nof the sound pulse) to a low-noise preamplifier, a gyrator filter with adjustable Q factor\nfrom 0 to 1000, a linear amplifier (0 - 40 dB), a log amplifier, and a signal shaper cir-\ncuit. The signal is then transmitted to an adjustable digital divider and to a period-\nmeter (interval timer) with an IEC-Bus interface. The minimum time interval of the period-\nmeter is 0.1 us. The timing considerations are exactly the same as in the temperature\nmeasurements. Consequently the vertical wind is measured approximately every 10 m.\nDATA ACQUISITION AND PROCESSING\n7.5\nThe RACES system uses a PDP11-03 16-bit minicomputer with 32-k-word RAM memory,\ndisplay, an LA 35 printer, and an RX02 floppy disk driver with two single-side, double-\ndensity disk drivers.\nThe operator can choose the time interval from 0 (immediate) to 60 minutes, the\nnumber of soundings for averages from 0 to 400, and whether to print all the data, the\nselected data, or the statistical data, or to keep the data on file in a second floppy\ndisk. A sample of the output is shown in Fig. 7.6.\nPURPOSE OF THE COMPARISONS\n7.6\nOur purpose in BLIE will be to compare the measurements made by the RACES\nsystem with those made by the conventional tower instruments and by other remote sensing\nsystems. It must, however, be considered that the RACES system has a sampling volume much\nlarger and a sampling time much shorter than those of conventional instruments on the\ntower.\nThe range of the RACES system used will be rather low (~150 m) because the high-\nlevel version is too bulky and too heavy to be transported easily overseas. Another\nreason for the low range will be that we will have only one UHF receiving antenna instead\nof five.\n45","300 SONDAGES\n04-SEP-79\n11:40:00\nHAUTEUR\nT - BAR\nSIGMA\nNB. DE MESURES\n(M)\n(DEG-C)\n(DEG-C)\nVALIDES (%)\n394.\n29.98\n0.00\n0.3\nI\nTI\n368.\n0.00\n0.00\n0.0\nI\nI\n343.\n25.32\n1.64\n0.7\nI\nT\nI\n317.\n24.76\n0.44\n0.7\nI\nT\nI\n291.\n27.26\n0.00\n0.3\nI\nT\nI\n265.\n27.69\n0.91\n1.3\nI\nT\nI\n239.\n28.99\n2.22\n2.3\nI\nT\nI\n213.\n28.23\n2.37\n3.7\nI\nT\nI\n186.\n27.35\n2.92\n4.7\nI\nT\nI\n160.\n27.95\n2.42\n5.3\nI\nT\nI\n134.\n27.51\n1.93\n10.7\nI\nT\nI\n108.\n27.91\n2.27\n13.0\nI\nT\nI\n82.\n28.09\n1.70\n24.3\nI\nT\nI\n56.\n28.68\n1.53\n61.3\nI\nT\nI\n30.\n28.42\n1.32\n95.7\nI\nT\nI\n20.00\n30.00\n300 SONDAGES\n04-SEP-79\n11:40:00\nHAUTEUR\nW - BAR\nSIGMA\nNB. DE MESURES\n(M)\n(M/S)\n(M/S)\nVALIDES (%)\n385.\n-0.44\n0.02\n1.3\nI\nW\nI\n372.\n0.00\n0.00\n0.0\nI\nI\n360.\n0.00\n0.00\n0.0\nI\nI\n347.\n0.00\n0.00\n0.0\nI\nI\n335.\n-0.46\n0.00\n1.0\nI\nW\nI\n322.\n0.00\n0.00\n0.0\nI\nI\n310.\n-0.17\n0.11\n2.0\nI\nW\nI\n298.\n0.00\n0.00\n0.0\nI\nI\n285.\n-0.33\n0.02\n1.0\nI\nW\nI\n273.\n-0.43\n0.01\n1.3\nI\nW\nI\n260.\n0.00\n0.00\n0.0\nI\nI\n248.\n0.00\n0.00\n0.0\nI\nI\n235.\n-0.29\n0.21\n3.0\nI\nW\nI\n223.\n0.00\n0.00\n0.0\nI\nI\n210.\n-0.49\n0.01\n1.3\nI\nW\nI\n197.\n-0.43\n0.01\n1.3\nI\nW\nI\n184.\n-0.23\n0.16\n2.7\nI\nW\nI\n171.\n0.00\n0.00\n0.0\nI\nI\n158.\n-0.35\n0.12\n1.3\nI\nW\nI\n145.\n-0.13\n0.13\n3.0\nI\nW\nI\n132.\n-0.06\n0.01\n1.3\nI\nW\nI\n119.\n0.00\n0.00\n0.0\nI\nI\n106.\n0.00\n0.00\n0.0\nI\nI\n93.\n0.22\n0.00\n1.3\nI\nW\nI\n80.\n0.00\n0.00\n0.0\nI\nI\n67.\n-0.01\n0.01\n1.7\nI\nW\nI\n54.\n-0.24\n0.01\n1.7\nI\nW\nI\n41.\n0.08\n0.02\n1.3\nI\nW\nI\n28.\n0.33\n0.02\n1.7\nI\nW\nT\n15.\n0.00\n0.00\n0.0\nI\nI\n-1.00\n1.00\nFigure 7.6.\nSample output sheet.\n46","8. FM-CW RADAR\nR. B. Chadwick and K. P. Moran\nNOAA/ERL/Wave Propagation Laboratory\nBoulder, Colorado, U.S.A.\nINTRODUCTION\n8.1\nThe frequency-modulated, continuous-wave (FM-CW) radar first developed by Richter\n(1969) combines high sensitivity necessary for detection of clear-air echoes with ultra-\nhigh resolution (<1 meter) and virtual freedom from ground clutter, features which cannot\nbe achieved in pulse radars used for monitoring atmospheric structures. Atlas et al.\n(1970), Gossard et al. (1970, 1971), and Bean et al. (1971) have described the use of this\nnew tool in studying a variety of micrometeorological processes. Recently, however, FM-CW\nsystems have enjoyed an added dimension: Doppler wind-measurement capability (e.g., Chad-\nwick et al., 1976a,b; Chadwick and Strauch, 1979). The system can be operated in two\nmodes: for high-resolution studies of atmospheric structure, the radar is operated in the\nrange-only mode (to measure reflectivity as a function of range); for wind profiling, the\nradar is operated in the range-Doppler mode. The two modes of operation use the same equip-\nment, differing only in sweep rates and sampling schemes.\nIn the range-only mode of operation, the antennas are usually pointed vertically,\ntypically providing a maximum range of about 3 km or less in clear air, but much greater in\nthe presence of targets such as hydrometeors, chaff, and insects. The WPL equipment pro-\nvides 500 range cells within this altitude, yielding cells and hence resolution about 6 m\nor less in range. The beamwidth is some 0.05 radians, so that the interrogated cells are\ngenerally shaped like thin discs. In the range-only mode of operation, the output displays\nshow regions of enhanced atmospheric refractive-index fluctuations. The time history of\nthese records reveals the advection of structures passing overhead within the PBL during\nthe observation period, as well as non-stationarity in the PBL itself (associated, for\nexample, with the rise of the convectively mixed layer during the morning hours) From the\nresulting data set it is very easy to discern layers of high refractive-index variability\nand the behavior of these layers during the day.\nIn the range-Doppler mode the antenna can either be aligned in a given fixed\ndirection or scanned in azimuth. The maximum range for clear-air measurements depends on\nthe elevation angle. Looking vertically, the maximum range is about 3 km and this maximum\nrange increases as the antenna beam is lowered toward the horizon. The number of range\ngates and the number of spectral points are variable, subject to the constraint that the\nproduct of range cells and the number of spectral points per range cell must equal 500,\nwhich is the number of points available at the output of the signal processor. Normally,\nten range cells with 50 spectral points each are used, providing radial wind velocity\nmeasurements at ten equally spaced intervals out to the maximum range. Such a measurement\nyields only the radial component of the wind, i.e., the wind component parallel to the\nantenna beam direction. To derive profiles of the total vector wind, the airspeeds are\nmeasured with the radar looking in two or more directions. Horizontal homogeneity of the\nwind field within the scanning volume is assumed. Wind-velocity measurements made while\nthe radar antenna is scanning azimuthally yield a so-called velocity-azimuth display (VAD)\nTotal wind profiles as well as convergence profiles and estimates of shearing and stretch-\ning deformation can be obtained from a VAD scan. The time required for one vertical pro-\nfile of wind speed and direction is 30 S. A large fraction of this time is expended in\nsteering the antenna. Doppler sensing of the radial wind component profile is relatively\nrapid, typically once per second.\nA recent improvement is the capability to operate the radar at very low elevation\nangles. Before these improvements, the minimum elevation angle was about 30° from horizontal.\nThe increased return from the ground clutter at lower elevation angles caused saturation\n47","Figure 8.] The transmitting and receiv-\ning antennas of the WPL FM-CW radar,\nshown pointed vertically. The BAO 300-m\ntower is in the background. The trailer\non the right houses the electronics for\nthe radar systems.\nof the signal processor. Now the radar can operate at an elevation angle of 5°. The\nmaximum range at these lower angles is greatly increased. In the summer-time clear air,\nranges exceeding 10 km are possible at 8° elevation angle. For hydrometeor return, the\nmaximum range can exceed 40 km. The radar has mapped thunderstorms at 40 km range.\nAs indicated above, the optically clear air targets for the FM-CW radar are half-\nradar-wavelength Fourier components of fluctuations in refractive index associated with\natmospheric turbulence. Of course the radar detects other targets, including hydrometeors,\ninsects, clouds, aircraft, and balloons. As a rule these other targets produce radar\nechoes of sufficiently distinctive character that they are readily distinguishable from\nclear-air returns, so that no misinterpretations arise. Indeed, to the extent that insects\nand chaff follow the mean flow, they simply increase the signal-to-noise ratio and actually\naid the wind measurement process. However, when the backscattered power exceeds a certain\nlevel, the signal processor saturates and quantitative wind and backscatter intensity\nmeasurements deteriorate in quality and reliability.\n8.2\nDETAILS OF THE WPL FM-CW RADAR\nThe Wave Propagation Laboratory FM-CW radar is mobile and transported on two\ntrailers. Figure 8.1 shows the radar receiving and transmitting antennas and their mount,\nwith the BAO tower in the background. The radar transmitter, receiver, and data processing\nelectronics are housed in a trailer that is not shown. The major parameters describing\nsystem performance are listed in Table 8.1. No maximum range is given since this depends\nupon atmospheric conditions and/or the availability of suitable targets, factors that vary\ndiurnally and seasonally.\nTable 8.1. FM-CW radar performance parameters\nAverage transmitted power\n200 W\nAntenna diameter\n2.44 m\nWavelength\n10 cm\nReceiver noise figure\n2.2 dB\nMinimum range\n15 m\nMinimum detectable signal\n-155 dBm\nRange resolution (adjustable)\n>1.65 m\nVelocity resolution (adjustable)\n>3 cm/s\n48","During the intercomparison experiment, the FM-CW radar will be operated at an\nelevation angle of 60° with a maximum range less than 3 km. This will provide height\ncoverage to about 2 km. Because of the requirement that wind profiles be available within\n24 h after they are taken, the data will be reduced by hand. This means the radar will be\noperated only during selected data-taking intervals, mostly during the day. Also, this\nwill preclude obtaining winds from the lowest range bin where special processing techniques\nare needed to determine the sign of the Doppler velocity.\nTo facilitate comparisons, the radar will be pointed either to the west or to the\nsouth during data-taking periods. While attempts will be made to measure both components\nfor a few 20-min periods, the normal mode of operation will be to measure only one compo-\nnent during one 20-min period.\nThe hand processing algorithm that determines which bin of the velocity spectrum\ncontains the peak assumes that the peak represents the mean value. This assumption could\nintroduce errors beyond those normally expected in an intercomparison such as this. The\nfirst type of error is that due to simple human error in locating the spectral peak. This\nwould normally be a large error. In some instances these points would be isolated; in\nother instances, the points in error may occur in sequences. Careful processing should\nminimize the occurrence of such errors. The second type of error is due to the discrete\nnature of the output velocity spectra and the fact that only 50 velocity values can be\nselected over the range of +10.5 m/s. This \"discreteness\" introduces errors in the range\nof +0.5 m/s. A third type of error is that caused by using the peak of a non-symmetric\nspectrum as the mean. The size of this error cannot be estimated without having some\nmeasure of the spectral asymmetry.\nThe radial velocity spectra taken by the FM-CW radar are on file and are avail-\nable to any BLIE participants.\n8.3 REFERENCES\nAtlas, D., J. I. Metcalf, J. H. Richter, and E. E. Gossard (1970): The birth of \"CAT\" and\nmicroscale turbulence. J. Atmos. Sci. 27:903-913.\nBean, B. R., R. E. McGavin, R. B. Chadwick, and B. D. Warner (1971): Preliminary results\nof utilizing the high resolution FM radar as a boundary layer probe. Boundary Layer\nMeteorol. 1:466-473.\nChadwick, R. B. K. P. Moran, R. G. Strauch, G. E. Morrison, and W. C. Campbell (1976a)\nMicrowave radar wind measurements in the clear air. Radio Sci. 11:795-802.\nChadwick, R. B., K. P. Moran, R. G. Strauch, G. E. Morrison, and W. C. Campbell (1976b)\nA new radar for measuring winds. Bull. Am. Meteorol. Soc. 57:1120-1125.\nChadwick, R. B., , K. P. Moran, G. E. Morrison, and W. C. Campbell (1978): Measurements\nshowing the feasibility for radar detection of hazardous wind shear at airports.\nTechnical Report AFGL-TR-78-0160, Air Force Geophysical Laboratories, Hanscom Air\nForce Base, Bedford, Mass.\nChadwick, R. B., and R. G. Strauch (1979): Processing of FM-CW Doppler radar signals from\ndistributed targets. IEEE Trans. Aerosp. Electron. Syst. AES-15:185-188.\nGossard, E. E., J. H. Richter, and D. Atlas (1970): Internal waves in the atmosphere from\nhigh-resolution radar measurements. J. Geophys. Res. 75:3523-3536.\nGossard, E. E., D. R. Jensen, and J. H. Richter (1971): An analytical study of tropo-\nspheric structure as seen by high-resolution radar. J. Atmos. Sci. 28:794-807.\nRichter, J. H. (1969): High resolution tropospheric radar sounder. Radio Sci. 4:1261-1268.\n49","9. DUAL-DOPPLER RADAR\nR. A. Kropfli\nNOAA/ERL/Wave Propagation Laboratory\nBoulder, Colorado\n9.1\nINTRODUCTION\nAlthough the Wave Propagation Laboratory developed its X-band dual-Doppler radars\nprimarily to study motion fields within precipitating clouds (e.g., Miller and Strauch,\n1974; Miller et al., 1975; Kropfli and Miller, 1976; Dye et al., 1978), the same radars\nhave also been applied in PBL studies, both in small experiments (e.g., Wilson, 1970;\nFrisch and Clifford, 1974; Gossard and Frisch, 1976), and as part of large field programs\nsuch as METROMEX (e.g., Kropfli and Kohn, 1978). In such studies the radars use either\nhydrometeors, such as snowflakes (Wilson, 1970), or artificial chaff (e.g., Gossard and\nFrisch, 1976; Kropfli and Kohn, 1978) as tracers, deducing wind velocities from the Doppler\nshifts measured in the echoes from these targets. Scanning the radars through large vol-\numes has provided a tremendous step forward in our visualization of boundary-layer flow\nfields.\nDespite the wide variety of field programs in which these radars have been used,\nthere has not been an opportunity until now to make detailed comparisons of the Doppler\nradar wind fields with data from other remote sensors or in-situ instruments. An experi-\nment called PHOENIX provided this opportunity in September of 1978, and the first results\nof this experiment are presented here. The focus of this experiment was a 300-m instru-\nmented tower, the Boulder Atmospheric Observatory (BAO) (Kaimal, 1978). The instruments on\nthis tower, along with other remote, ground-based, and aircraft-borne sensors, were used in\nthese intercomparisons\nOne of the many components of PHOENIX was an array of three Doppler radars: two\nNOAA/WPL X-band radars, and an NCAR C-band (CP-4) radar. Analyses described here involve\nonly the two X-band radars. These radars were located to optimize observations near the\n300-m-high, instrumented BAO tower. Short (~15-km) radar baselines were chosen to optimize\nspatial resolution, a luxury not possible in past multiple Doppler radar experiments.\nIn addition to these intercomparisons, an important goal of PHOENIX was to im-\nprove our understanding of physical processes in the PBL. Understanding of a physical\nprocess almost always follows our ability to observe and measure that process in a better\nway. We are therefore hopeful that the first PBL flow visualizations presented here, and\nthe ones that will be produced later, will be followed by a corresponding increase in our\nunderstanding of the PBL.\n9.2\nDESCRIPTION OF THE EXPERIMENT\nSince the backscattered signal from the convective PBL is usually too weak to be\nobserved reliably by the radars involved in PHOENIX, chaff must be dispensed from an air-\ncraft over an area of several hundred square kilometers. X-band chaff was distributed for\nseveral hours at a time along 15-km crosswind flight legs. Usually, the flight patterns\nwere adjusted to dispense chaff about 30 to 45 min upwind of the target area. When the\nwinds were weak and variable in direction, a zig-zag pattern covering an appropriate box\nwas chosen. Convective activity was usually sufficiently strong between 1100 and 1800 (all\ntimes are given in MDT) each day to disperse the chaff uniformly throughout the convective\nPBL in the test area. Radar echoes from the resulting chaff cloud were usually greater\nthan 10 dB above noise power within most of the region of interest. The two identical NOAA\nsystems were operating at a wavelength of 3.22 cm, peak transmitted power of 20 kW, pulse\nwidth of 1.0 us, and beamwidth of 0.8°.\n50","287\n+\nDoppler Radar\nT BAO Tower\nI25\nOptical Triangle Sites\nLongmont\nNOAA Radar\n26\n27\n25\n23\n24\n52\n52\n19 20 21\n22\n18\n13\n14\n15\n16\n17\n12T\nBoulder\n9 10\n11\n7\n8\n3\n4 5\n6\nNCAR Radar\n1\n2\n7\nNOAA Radar\nBaseline Road\n7\nis\nLafayette\n7\nSo. Boulder Road\n287\nNorth\nI25\n10\n5\n0\n5\nKilometers\nFigure 9.1. Positions of radars and optical triangle relative to BAO tower.\nPAM stations are indicated by numbers.\nFigure 9.1 shows the location of the radars relative to the tower. The NCAR\nportable automated mesonetwork (PAM) and the NOAA optical triangle are also shown. The 13-\nto 18-km separation between radars is much smaller than is normally used in multiple Dop-\npler radar experiments. Thus, the radars were able to scan the entire depth of the PBL\n(~2 km) over an area of several hundred square kilometers while observing air motions at\nwavelengths as small as 600 or 700 m. Volume scans were completed in less than 90 S\nSiting the radars equidistant from the tower also had the important advantage of equalizing\nthe radial and tangential dimensions of the three radar pulse volumes to about 150 m at the\nBAO.\n51","Table 9.1. Summary of radar scan characteristics for PHOENIX\nScan number/name\nVolume time\nCartesian grid\nSample density\nHalf-amplitude\nArea covered\n(s)\nelement , AY, AZ\nnumber (km³)\n(km2)\nwavelength after\n(km)\nfiltering (km)\n100/Standard\n72<T<96\n0.25, 0.25, 0.20\n170<N<270\n0.85\n20<A<110\n200/Fast-standard\n40<T<80\n0.20, 0.20, 0.20\n300<N<400\n0.70\n20<A<110\n300/Over-sampled\n40<T<90\n0.15, 0.15, 0.15\n600<N<1300\n0.50\nA 4\n400/Optical triangle\n50<T<180\n160<N<300\nA 25\n600/Large scale\n140<T<180\n0.40, 0.40, 0.30\n80<N<160\n1.40\nA 270\nFigure 9.2. Schematic representation of\nCOPLAN scanning method.\nFive different scan types, summarized in Table 9.1, were designed in order to\nsatisfy the experimental objectives and, in addition, to allow us to evaluate the relative\nmerits of different radar sampling schemes for future experiments. The routine that was\nfollowed throughout the experiment was to perform pairs of the five scans as rapidly as\npossible. Taking two identical volume scans in rapid succession has, in effect, given us\nthe redundant data set that is helpful in distinguishing statistical fluctuations in the\nmeasurement from actual features in the flow field. It also allows convenient temporal\ninterpolations between scans whenever necessary. Each pair of scans was completed in about\n3 min and the entire sequence was completed in 15 to 20 min. All scans were predetermined\nto reduce operator errors.\nThe two NOAA radars operated during the entire PHOENIX experiment in the COPLAN\nscanning mode (Miller and Strauch, 1975), as shown in Fig. 9.2. Specifically, they scanned\nin tilted planes passing through the baseline between them. Having taken the data in this\nfashion provides the option of either COPLAN or Cartesian processing with the existing\nsoftware.\nOf the wide variety of processing options available to generate three-dimensional\nwind fields, we chose the following sequence: 1) computation of mean radial velocity\nestimates for each radar by a pulse-pair method (Rummler, 1968), 2) thresholding the\npulse-pair velocities to eliminate noise-contaminated estimates, 3) interpolation to a\ncommon Cartesian grid so that the radial velocities can be vectorially combined to yield\ntwo-dimensional velocity and divergence fields within each horizontal plane, and 4) inte-\ngration of the anelastic continuity equation in Cartesian coordinates to yield the vertical\nvelocity component. The integration is performed with the usual boundary conditions; i.e.,\nthe vertical velocity is zero everywhere at the surface. Many refinements are currently\nbeing added to this process.\n52","4.5\n4.5\n4.0\n4.0\n3.5\n3.5\n3.0\n3.0\n2.5\n2.5\n2.0\n2.0\n1.5\n1.5\n1.0\n1.0\n5\n5\n.00\n00\n-.5\n-5\n-1.0\n-1.0\n-1.5\n-15\n2.0 m/s\n2.0 m/s\n-2.0\n-2.0\n-2.5\n-2.5\n4.5\n4.5\n4.0\n4.0\n3.5\n3.5\n3.0\n30\n2.5\n2.5\n2.0\n2.0\n1.5\n1.5\n1.0\n1.0\n.5\n5\n.00\n00\n-.5\n-.5\n-1.0\n-1.0\n-1.5\n-1.5\n2.0 m/s\n2.0 m/s\n-2.0\n-2.0\n-2.5\n-2.5\n-3.0 -2.5 -2.0 1.5 -1.0 -5 00 5 1.0 1.5 2.0 2.5 3.6 3.5 4.0\n-3.0 -2.5 -2.0 1.5 -1.0 -.5 .00 5 1.0 1.5 2.0 2.5 3.0 3.5 4.0\nDistance East of Tower (km)\nDistance East of Tower (km)\nFigure 9.3. Horizontal eddy wind fields\nFigure 9.4. Horizontal eddy wind fields\n(volume mean removed) for Z=0.1 km at\n(volume mean removed) for Z=0.1 km at\n1512 MDT (top) and at 1513 MDT (bottom)\n1531 (top) and at 1533 (bottom) MDT on\n21 September 1978.\non 21 September 1978.\n9.3\nINTERCOMPARISONS\nFigure 9.3 shows the eddy flow patterns (volume mean removed) for two scans that\nwere begun about 1 min apart. Clearly, their appearances are very similar. In Fig. 9.4\nwe have shown two similar wind field patterns 20 min later, and again the repeatability\nis excellent. This is borne out even when looking at the vertical cross sections as in\nFig. 9.5. It is reassuring to observe this short-term repeatability while the entire\npattern changes completely during the 20-min interval. The RMS difference between U, V,\nand W wind components generated by scans such as these is about 0.3 m/s.\nComparisons of wind components derived from the radars were made with those\nmeasured by a sonic anemometer at the 300-m level on the BAO tower (Kaimal, 1978)\nFigure 9.6 shows these results. The tower data were obtained by averaging the sonic\nanemometer record for 90 S, the time required for an air parcel to pass through one radar\n53","1.5\n1.5\n1.0\n1.0\n.5\n.5\n.0\n.0\n-3.0\n-2,5\n-2.0\n-1.5\n-1.0\n-.5\n.00\n.5\n1.0\n1.5\n2.0\n2.5\n3.0\n3.5\n4.0\n-3.0\n-2.5\n-2.0\n-1.5\n-1.0\n-.5\n.00\n.5\n1.0\n1.5\n2.0\n2.5\n3.0\n3.5\n4.0\nDistance East of Tower (km)\nFigure 9.5. Vertical (XZ) sections through the wind field at 1531 (left) and\n1533 (right) MDT on 21 September 1978 for Y=0.5 km.\n(b)\n(a)\n3.0\n3.0\n2.0\n2.0\n1.0\n1.0\n-1.0\n-3.0\n-2.0\n1.0\n2.0\n3.0\n-3.0\n-2.0\n-1.0\n1.0\n2.0\n3.0\nU Radar (m/s)\nW Radar (m/s)\n1.0\n100 Series\n-1.0\n100 Series\n200 Series\n200 Series\n300 Series\n300 Series\n-2.0\n-2.0\n-3.0\n-3.0\n(c)\n3.0\n2.0\n1.0\n-3.0\n-2.0\n-1.0\n1.0\n2.0\n3.0\nV Radar (m/s)\n100 Series\n-1.0\n200 Series\n300 Series\nFigure 9.6. Scatter plots of the\n-2.0\ncomponents from the tower at the\n300-m level with components from\n-3.0\nthe dual-Doppler radar analysis :\n(a) U component; (b) W component;\n(c) V component.\n54","grid volume. The two methods generally agree to within 0.5 m/s despite the volume aver-\naging by the radar, as opposed to the line average represented by the tower values. There\nis a slight underestimation in the magnitudes of the three components, which could be the\nresult of this volume averaging and ground-clutter biasing.\nWhenever comparisons of radar- and aircraft-derived fields are made two problems\nshould be considered to ensure accurate and valid comparisons. First, the aircraft must be\npositioned accurately in time and space with respect to the radar data. Spatial agreement\nwithin at least 0.2 km and temporal agreement within 1 min are needed for the assumption of\nstationarity of the turbulent wind fields to be valid. For differences much larger than\nabout 0.2 km and 1 min, changes can occur that seriously degrade the comparison of radar\nand aircraft data. Although the inertial navigation system of the aircraft can drift\nsignificantly, visual fixes were used in this experiment to correct the aircraft locations\nto within 0.2 km. Even though every effort was taken to produce simultaneous measurements,\nsome data comparisons had to be made with aircraft and radar data separated by as much as\n2 to 3 min.\nThe second problem to be considered is that of filtering aircraft and radar data\nsuch that the spectral content is as similar as possible. The aircraft velocity data are\ncollected at a rate of about 20 Hz, with the samples being essentially independent. The\nradars collected radial velocity data that were interpolated to Cartesian grids having grid\nelements 200 or 250 m on a side. These radar data were processed as described in the\npreceding section. In order to match the radar-derived scales, a Gaussian filter with a\nhalf width of 0.2-km was applied to the aircraft data.\nSample comparisons of multiple Doppler radar data and aircraft data are presented\nin Figs. 9.7 and 9.8. Single data points have been added in Fig. 9.7 to indicate BAO tower\nwind values (The tower is 0.75 km north of the east-west flight track.) These measurements\nand others like them indicate agreement between multiple Doppler radar, aircraft, and tower\nmeasurements to better than 1 m/s in most cases.\n2\n(u)\n0\n-2\n2\n(v)\n0\nFigure 9.7. Comparison of wind com-\n-2\nponents (U, V, and W) derived from\nDoppler data (at 1100 hours) and\n1\n(w)\naircraft data (at 1108 to 1110) on\nthe same day. Solid lines repre-\nsent aircraft data; dashed lines\n0\nrepresent radar data. Heights are\n0.15, 0.10, and 0.50 km for radar,\naircraft, and inversion respec-\n-1\ntively. BAO tower data are in-\ndicated by * (at 0.1 km) and\n(at 0.15 km)\n2\n3\n-2\n-1\n0\n1\nDistance East of Tower (km)\n55","-2\n(u)\n-4\n-6\n6\n(v)\n4\n2\n0\n2\n(w)\n-1\n0\nFigure 9.8. Comparison of wind com-\nponents derived from Doppler data\n(at 1335 hours) and aircraft data\n(at 1336 to 1338) as in Fig. 9.7.\n-1\nHeights are 0.5, 0.6, and 0.8 km\nfor radar, aircraft, and inver-\nsion, respectively.\n-2\n-1\n0\n1\n2\n3\nDistance East of Tower (km)\n9.4\nFLOW VISUALIZATION IN THE PLANETARY BOUNDARY LAYER\nFigure 9.9 is an example of how the use of the various scan types summarized in\nTable 9.1 allows us to see the PBL motions with different magnifications. The figure\ncontains a large-scale 600 series scan, a 200 series scan, and a high-resolution 300\nseries scan, all taken within 8 min. Boxes have been drawn over the 600 series grid to\nindicate where the 200 and 300 series grids lie. The same features seen in the 600 series\ngrid can be seen with increased detail in the 200 series. The 600 series display shows a\nvery chaotic wind field with sharp wind gradients aligned roughly along the mean wind\ndirection, which was 2.8 m/s from the SSE. Scales of motion here are about 3 km or about\nthree times the depth of the convective boundary layer at this time.\nAn example of an unusual feature, suggestive of flow around a jet, is depicted in\nthe 200 series and 300 series displays of Fig. 9.10. An updraft of about 1.5 m/s was\nobserved by radar at the location (0.5, 0.8) at a height of 0.825 km. Such a weak updraft\nwould not be expected to act as a barrier to the prevailing flow. This feature was clearly\nevident in the wind patterns for about 10 min and was observed to track with the mean wind.\nRecognizable features in the eddy field could usually be tracked along the mean wind for\nabout 10 or 15 min.\n56","300 Series\nHigh Resolution\n1.63\nZ 0.075 km\nT 1522\n1.03\n0.43\n-0.18\n-0.78\n-1.38\n2.0 m/s\n1.63\n-1.38\n-0.78\n-0.18\n0.43\n1.03\n600 Series\n200 Series\n8.0\n4.0\nLow Resolution\nMedium Resolution\nZ 0.150 km\nZ = 0.100 km\n6.0\nT 1525\n3.0\nT 1517\n4.0\n2.0\n2.0\n1.0\n0.0\n0.0\n-2.0\n-1.0\n-4.0\n2.0 m/s\n-2.0\n2.0 m/s\n4.0\n-8.0\n-6.0\n-4.0\n-2.0\n0.0\n2.0\n-3.0\n-2.0\n-1.0\n0.0\n1.0\n2.0\n3.0\n4.0\nFigure 9.9. Horizontal eddy fields at high, medium, and low resolutions.\n4\n2 m/s\n3\n1.0\n2\n0.5\nFigure 9 .10. Horizontal eddy\n1\n0\nfields on 21 September 1978:\n(left) at Z=0.9 km, obtained\n0\n-0.5\nfrom 200 series scan at 1538;\n(right) at Z=0.825, obtained\n-1\n-1.0\nfrom 300 series scan at 1540.\n0\n0.5\n1.0\n-2\n0\n1\n2\n3\n-1.0\n-0.5\nkm East of BAO\nkm East of BAO\n57","9.5\nSUMMARY\nWe have presented a brief description of the dual-Doppler technique for measuring\nthree-dimensional wind fields, intercomparisons with other in-situ measurements of the\nthree wind components, and a sample of the flow fields obtained during the recent PHOENIX\nexperiment at the BAO. Although the analysis of these data is far from complete, we expect\nthese data and similar data sets to have important impacts on remote sensor techniques and\nalso on our understanding of the dynamics of the PBL.\n9.6\nREFERENCES\nDye, J. E., L. J. Miller, B. E. Martner, and Z. Levin (1978): Growth and recirculation of\nprecipitation in an evolving convective storm. Prepr. Conf. on Cloud Phys. and Atmos.\nElectr., 31 July-4 August 1978, Issaquah, Washington, American Meteorological Soci-\nety, Boston, Mass., pp. 528-533.\nFrisch, A. S., and S. F. Clifford (1974): A study of convection capped by a stable layer\nusing Doppler radar and acoustic echo sounders. J. Atmos. Sci. 31:1622-1628.\nGossard, E. E., , and A. S. Frisch (1976): Kinematic models of a dry convective boundary\nlayer compared with dual-Doppler radar observations of wind fields. Boundary Layer\nMeteorol. 10:311-330.\nKaimal, J. C. (1978): NOAA instrumentation at the Boulder Atmospheric Observatory. Prepr.\n4th Symp. Meteorol. Obs. and Instrum., 10-14 April 1978, Denver, Colorado, American\nMeteorological Society, Boston, Mass., pp. 35-40.\nKropfli, R. A., , and N. M. Kohn (1978): Persistent horizontal rolls in the urban mixed\nlayer as revealed by dual-Doppler radar. J. Appl. Meteorol. 17:669-676.\nKropfli, R. A., and L. J. Miller (1976): Kinematic structure and flux quantities in a\nconvective storm from dual-Doppler radar observation. J. Atmos. Sci. 33:520-529.\nMiller, L. J., and R. G. Strauch (1974) : A dual-Doppler radar method for the determination\nof wind velocities within precipitating weather systems. Remote Sensing Env. 3:219-\n235.\nMiller, L. J., J. D. Marwitz, and J. C. Fankhauser (1975) Kinematic structure of a\nColorado thunderstorm. Prepr. 16th Radar Meteorol. Conf., 22-24 April, Houston,\nTexas, American Meteorological Society, Boston, Mass., pp. 128-133.\nRummler, W. 0. (1968): Two pulse spectral measurements. Tech. Memo. MM-68-4121, Bell\nTelephone Laboratories, Whippany, N.J.\nWilson, D. A. (1970): Doppler radar studies of boundary layer word profile and turbulence\nin snow conditions. Prepr. 14th Radar Meteorol. Conf., Tucson, Arizona, American\nMeteorological Society, Boston, Mass., , pp. 191-196.\n58","10. REMOTE SENSING OF TEMPERATURE PROFILES WITH COMBINED\nACTIVE AND PASSIVE SENSORS\nM. T. Decker\nNOAA/ERL/Wave Propagation Laboratory\nBoulder, Colorado, U.S.A.\n10.1\nINTRODUCTION\nProject PHOENIX (Hooke, 1979), carried out at the Boulder Atmospheric Observa-\ntory (BAO) during September 1978, involved a variety of atmospheric sensors including\naircraft, the NCAR PAM network, radars, lidar, acoustic sounders, microwave radiometers,\noptical wind sensors, radiosondes and fixed level balloons, and the 300-m BAO instrumented\ntower. The many goals of this project included evaluation and comparison of various remote\nsensing systems. Among these was the comparison of atmospheric temperature profiles ob-\ntained from microwave radiometers with profiles from standard tower and radiosonde sensors,\nand especially the usefulness of information from active sensors such as microwave radars\nand acoustic sounders in improving the resolution of vertical structure in the radiometric\ntemperature profiles. It will be shown that the active sensor information can indeed be\nuseful but that questions remain regarding the proper interpretation of the observed\nechoes.\nINSTRUMENTATION\n10.2\nThe measurements reported here were made by microwave radiometer, FM-CW radar,\nand radiosondes colocated at the BAO site. Radiosonde equipment was a standard GMD\nsystem operated by the NCAR Field Observing Facility, and 38 flights were made during the\nmonth.\nThree microwave radiometer systems were operated at the BAO site during the\nPHOENIX experiment. Data reported here are from the Scanning Microwave Spectrometer\n(SCAMS) operated by personnel from the Jet Propulsion Laboratory. This is a 5-channel\ninstrument similar to that flown aboard the Nimbus 6 satellite. It has one frequency at\nthe water vapor absorption line at 22.235 GHz, three frequencies (52.85, 53.85, and 55.45\nGHz) in the oxygen absorption complex, and a frequency of 31.65 GHz in the window between\nthese absorption bands. The instrument scans in a vertical plane from a zenith angle of\n58.3 through the zenith, and to 28.1° on the other side of zenith. The scan steps in\n7.2° increments with a dwell time of about 1 S at each step. Two additional steps are\nused to point the antennas at calibration targets, and the entire sequence is repeated\napproximately once each 16 S. The sky radiation measurements for all channels at zenith\nand for 55.45 GHz at 58.3° zenith angle were used to retrieve the temperature profiles\nreported here. The 1-s measurements (at 16-s intervals) were averaged over a period of\nabout 7 min before being used in the profile retrieval algorithm.\nThe FM-CW radar was operated during PHOENIX by the NOAA Wave Propagation Labora-\ntory. This radar (Chadwick et al., 1976) operates at a wavelength of 10 cm with an aver-\nage transmitted power of 200 W. The 2.44-m transmit and receive antennas are steerable in\nelevation and azimuth. The radar operates in either of two modes: a high-resolution\nrange-only mode or a range-Doppler mode with a wind-measurement capability. In the meas-\nurements reported here the radar operated in the range-only mode with the antennas pointed\nat the zenith. The high-sensitivity, high-resolution, low-ground-clutter qualities of\nthis radar allow detection of the detailed structure of atmospheric refractive-index\nfluctuations in the lower atmosphere. Minimum range is 15 m, and in clear air the typical\nmaximum range is 3 km. The presence of persistent layer echoes is used here as evidence\nof thermal structure, specifically an elevated temperature inversion.\n59","3.0\n3.0\nProject Phoenix\nProject Phoenix\n11 Sept 1978\n7 Sept 1978\n2.5\n2.5\nRadiometer\n2.0\n2.0\nRadiosonde\nRadiosonde\nRadiometer\n1.5\n1.5\n1.0\n1.0\n0.5\n0.5\n0\n0\n-10\n0\n10\n10\n20\n0\n30\n10\n20\n30\nTemperature (C)\nTemperature (C)\nFigure 10.1. Comparison of radiosonde\nFigure 10.2. Comparison of radiosonde\nand radiometer temperature profiles\nand radiometer temperature profiles\nfor a case with simple vertical\nfor the case of a ground-based inver-\nstructure.\nsion.\n10.3\nTEMPERATURE PROFILE RETRIEVAL\nStatistical retrieval algorithms (Waters et al. , 1975; Westwater et al. , 1975)\nare used to extract temperature profiles from the radiation measurements In these algo-\nrithms we use a nine-element data vector consisting of the six radiation measurements as\nwell as surface temperature, pressure, and relative humidity to obtain a minimum variance\nestimate of the temperature at any level. The available measurement frequencies also\nallow us to correct for the effect of radiation from clouds as described by Westwater et\nal. (1976). Examples of the effectiveness of this cloud correction technique are con-\ntained in a series of measurements reported by Decker et al. (1978). It has been further\ndemonstrated by Westwater (1978) that if the presence and height of an elevated tempera-\nture inversion can be observed, the retrieval algorithm may be derived from a statistical\nensemble of atmospheres all of which contain temperature inversions at this height (or\nrealistically, within some representative height range). This method of conditional\nstatistics has been applied to a number of cases from PHOENIX, and examples are shown here.\n10.4\nRESULTS\nA sample comparison of temperature profiles from the radiometer and radiosonde\nfor a case with little vertical structure is shown in Fig. 10.1. In the example of Fig.\n10.2 the profile shows a ground-based temperature inversion. In cases such as these the\nradiometer profile is generally in good agreement with the radiosonde profile. An example\nof an elevated temperature inversion is shown in Fig. 10.3. In this case the structure of\nthe profile is smoothed by the radiometer to the extent that the temperature inversion is\nnot observed. It is in this type of profile that knowledge of inversion height would be a\nvery useful piece of information. The FM-CW radar record at this time shows a persistent\necho with maximum intensity at 507 m above the surface. The profile retrieval algorithm is\n60","3.0\n3.0\nProject Phoenix\nProject Phoenix\n18 Sept 1978\n18 Sept 1978\n2.5\n2.5\nRadiometer\n2.0\n2.0\nWith Height\nInformation\n1.5\n1.5\n1.0\n1.0\nRadiosonde\nRadiosonde\n0.5\n0.5\nRadiometer\n0\n0\n-10\n0\n10\n20\n30\n30\n10\n20\n-10\n0\nTemperature (C)\nTemperature (C)\nFigure 10.4. Comparison of radiosonde\nFigure 10.3. Comparison of radiosonde\nand radiometer temperature profiles\nand radiometer temperature profiles\nfor the case of an elevated inver-\nfor the case of an elevated inversion.\nsion, in which the radiometer profile\nis retrieved with knowledge of the\nheight of the temperature inversion\nderived from radar echoes.\nthen derived from a statistical ensemble, each member of which contains an elevated inver-\nsion with base in the height range from 400 to 600 m above the surface at Denver, Colorado.\nThe profile retrieval resulting from the use of this algorithm is shown in Fig. 10.4. This\nprofile is an improved representation of the radiosonde profile, and it is evident that the\ninversion height information has been helpful. It should be noted that the 200-m interval\nwas used in the statistical ensemble so that enough profiles could be found in our data\nbase to give a representative sample. A larger data base would allow this interval to be\nnarrowed and presumably improve the retrieved radiometer profile.\nIt must be pointed out that the above procedure required the assumption that the\necho observed by the FM-CW radar was associated with an elevated temperature inversion.\nSuch, of course, is not always the case; in fact, at the time of the profile of Fig. 10.2\nthe radar was observing an echo at a height of 157 m. If it is assumed that this echo is\nassociated with an elevated inversion rather than the ground-based inversion, and the tem-\nperature retrieval is performed using conditional statistics with inversions between 100\nand 300 m, the resulting profile is as shown in Fig. 10.5. It is obvious (when Fig. 10.5\nis compared with Fig. 10.2 that this procedure has degraded the radiometrically retrieved\nprofile. In view of a number of examples such as this observed during PHOENIX, additional\nwork must be done to assure proper use of the echo height data. Methods for characterizing\nthe echo data are being studied. A more basic study of the relation between the radio re-\nfractive index structure parameter which is observed by the radar and the profile or gra- -\ndient of refractive index which is related to temperature and water vapor is being pursued.\nIt is expected that the combination of active and passive sensors will result in improved\nremote sensing of profiles for research and operational use.\n61","3.0\nProject Phoenix\n7 Sept 1978\n2.5\n2.0\nRadiometer\nWith Height\n1.5\nInformation\n1.0\nRadiosonde\n0.5\nFigure 10.5. Comparison of radiosonde pro- -\nfile from Fig. 2 with radiometer profile\nderived with incorrect use of radar echo\n0\ninformation.\n-10\n0\n10\n20\n30\nTemperature (°C)\n10.5\nACKNOWLEDGMENTS\nThe radiometric measurements used here were made under the direction of Bruce L.\nGary of the Jet Propulsion Laboratory, Pasadena, California. Russell B. Chadwick directed\nthe work with FM-CW radar; Ed R. Westwater developed the retrieval algorithms for the radi-\nometer data. Both are with the NOAA/ERL Wave Propagation Laboratory.\n10.6\nREFERENCES\nChadwick, R. B. K. P. Moran, R. G. Strauch, G. E. Morrison, and W. C. Campbell (1976):\nMicrowave radar wind measurements in the clear air. Radio Sci. 11:795-802. -\nDecker, M. T. E. R. Westwater, and F. 0. Guiraud (1978): Experimental evaluation of\nground-based microwave radiometric sensing of atmospheric temperature and water vapor\nprofiles. J. Appl. Meteorol. 17:1788-1795.\nHooke, W. H. (ed.) (1979): Project PHOENIX: The September 1978 Field Operation. NOAA/\nNCAR Boulder Atmospheric Observatory Rept. No. 1, available from NOAA/ERL, Boulder,\nColo. 80303, and from NCAR Publications Office, Boulder, Colo. 80307.\nWaters, J. W., , K. F. Kunzi, R. L. Pettyjohn, R. K. L. Poon, and D. H. Staelin (1975):\nRemote sensing of atmospheric temperature profiles with the Nimbus 5 microwave spec-\ntrometer. J. Atmos. Sci. 32:1953-1959.\nWestwater, E. R. , J. B. Snider, and A. V. Carlson (1975): Experimental determination of\ntemperature profiles by ground-based radiometry. J. Appl. Meteorol. 14:524-539.\nWestwater, E. R., M. T. Decker, and F. 0. Guiraud (1976): Feasibility of atmospheric\ntemperature sensing from ocean data buoys by microwave radiometry. NOAA Tech. Rept.\nERL 375-WPL 48, NOAA/ERL, Boulder, Colo. [NTIS No. 262-421].\nWestwater, E. R. (1978): Improved determination of vertical temperature profiles of the\natmosphere by a combination of radiometric and active ground-based remote sensors.\n4th Symp. on Meteorol. Obs. and Instrum., 10-14 April 1978, Denver, Colo., , American\nMeteorological Society, Boston, Mass. , pp. 153-157.\n62","11. WPL DOPPLER SOUNDER\nW. D. Neff, H. E. Ramm,* and C. Wendt\nNOAA/ERL/Wave Propagation Laboratory\nBoulder, Colorado, U.S.A.\nINTRODUCTION\n11.1\nThis paper describes the use of the \"complex covariance\" frequency estimation\ntechnique in a microprocessor-controlled acoustic sounding system. A bistatic scattering\narrangement was used during BLIE with fan-beam transmitters, a central receiver, and two\northogonal 300-m baselines. A frequency of 1250 Hz with a 100-ms pulse of 300 electrical\nwatts was implemented.\nThe Wave Propagation Laboratory has developed and tested a number of Doppler\nacoustic sounders during the past ten years. These used a variety of frequency estimation\ntechniques and transmitter-receiver configurations. Direct spectral calculation, analog\ntracking devices (Kaimal and Haugen, 1977), and adaptive filter techniques were utilized.\nHowever, all these techniques required either expensive microcomputers or hardware to\nimplement. With the development of microprocessors capable of using higher-level languages\nsuch as Fortran, an effort began in this laboratory to reduce the complexity and expense of\nDoppler sounding systems.\nOwens (1977) simplified the acoustic sounder electronics to a single printed\ncircuit board and examined a simple frequency estimation technique referred to as \"real\ncovariance\" for possible implementation with an LSI-11 microprocessor. The simplicity of\nthe technique and the hardware developed by Owens led to more extensive field tests during\nthe September 1978 Project PHOENIX experiment (Neff and Brown, 1979) However, these\ncomparisons with tower data showed a systematic bias, leading to further laboratory testing\nin early 1979. Both real and complex covariance techniques were analyzed for the effect of\nwhite noise on the mean and variance of the frequency estimates. This analysis led to the\nchoice of complex covariance as the preferred technique and the basis for the system de-\nscribed in this paper. An outline of the system to be described in the following sections\nis shown schematically in Fig. 11.1.\nSYSTEM DESIGN AND DOPPLER ALGORITHMS\n11.2\nThe hardware for this system, with slight modification, was developed by E. J.\nOwens of WPL (Owens, 1977; also E. J. Owens, NOAA/ERL, Boulder, Colo., , personal communica-\ntion). Owens developed separate printed circuit boards for the acoustic sounder electron-\nics and for the heterodyning and filtering of the signals required for the real covariance\nfrequency estimation technique. Corresponding software was written for the 1978 Project\nPHOENIX experiment (Neff and Brown, 1979).\nThe basis for the real covariance technique is the following algorithm (Owens,\n1977):\nN-1\nA\nA\ni\ni+1\n1\n-1\nN\ni=1\n(11.1)\nf\nAf =\ncos\n-\n2TT\nN-1\nN\nC\nS\n{\nAj\nA\ni\ni=1\nNOAA Commissioned Officer assigned to WPL.\n63","where Is is the sampling period, fc the heteordyned carrier frequency, N the number of\nsamples, and A the discrete sample of the signal. Sampling frequencies range from 500 to\n1000 Hz, corresponding to reduced center frequencies of 125 or 250 Hz. The large number of\nsamples results in either large memory requirements or a reduced number of samples per\nrange gate to allow time for processing.\nThe complex covariance technique is based on the following algorithm (Sirmans and\nBumgarner, 1975):\n(Q i+1 - Qi I\n1\ni=1\ntan-1\n(11.2)\nS\n(Q.\ni1\n+\nI\nI\ni\ni=1\n2000-Hz Tone Burst\nPA\nf3\nReceived Signal\nPA\nf2\nf1\nSwitch\n1250-Hz\nTone Burst\nR\nPA\n(T3)\nT2\nT1\nArray Leg-Flag\nMonostatic\nBistatic\nEchosounder\nLSI-11 Microprocessor\nNoise\nand\nFloppy\nDoppler Board\nQuadrature\nDisk\nIn-Phase\nDoppler Signals\nFax\nDecWriter\nRecorder\nFigure 11.1 1. Block diagram of LSI-1l-controlled Doppler sounder.\n64","where the complex time signal Z, ( Ii + iQ) is given by\n() 2w o + sin t i 2w o\nIn this application, after the received signal is filtered (with a 300-Hz bandwidth) it is\nmultiplied first by the carrier and then separately by the carrier phase-shifted 90 de-\ngrees, providing the in-phase and quadrature components required in (11.2). After mixing, a\nlow-pass filter (0 + 200 Hz at the -3 dB point) provides the final processing of the\nsignals going to the computer, where the Nyquist frequency must be near the half-power\npoint in the bandpass of these filters to avoid aliasing by the noise (R. J. Keeler, NOAA/\nERL, Boulder, Colo., personal communication).\nFirst-moment spectral estimators do not provide any information as to the noise\ncontent of the spectrum. A variety of techniques can be used to provide an approximate\nestimate of the signal-to-noise ratio. In our case we filtered and detected the noise\nbelow 1 kHz. Since normal background noise falls off with increasing frequency, we ad-\njusted the gain of the noise circuit to match the output of the signal circuit with the\ntransmitters shut off. By using a broadband filter for the noise, we eliminated Doppler\nshifts calculated from nonwhite noise transients. Under most conditions, we observed that\nthe variations in noise estimate between these two techniques were about 25 percent.\nA bistatic sounding arrangement similar to that described by Kaimal and Haugen\n(1977) was utilized. The fan-beam transmitters operated at 1250 Hz. The central receiver\nnormally also acts as a monostatic transmitter at 2000 Hz. These choices of frequencies\nappear to avoid aliasing problems in the processing of the data. At present we do not\ncalculate the vertical velocity, but rather assume that it averages to zero.\nDIGITAL PROCESSING\n11.3\nThe details of the microprocessor system and its interfacing with an acoustic\nsounder have been provided by Owens (1977). To process complex covariance data we designed\na general purpose program to sample a variety of acoustic data as well as the in-phase and\nquadrature components for use in equation (11.2) at 200 Hz and several additional channels at\n100 Hz. These latter channels were used for the monostatic and bistatic intensities as\nwell as the noise channel. An assembly language program is called shortly after the trans-\nmit gate. After the maximum range gate is reached, control is returned to the Fortran main\nprogram, signal-to-noise tests applied, and frequency shifts calculated and accumulated for\na specified number of pulse repetition periods. For a maximum range of 600 m, a pulse\nrepetition period of 5 S is used, with the last second dedicated to the Fortran processing.\nFollowing the required averaging period (normally 18 min) the wind components, speed, and\nazimuth are obtained from the individual components. These data, together with the signal\nintensities, noise level, and number of samples retained for each range gate, are printed\nout and also recorded on floppy disk for later analysis. A line-printer profile of wind\nspeed and direction is also obtained for a quick visual impression of the data as shown in\nFig. 11.2.\nSIGNAL-TO-NOISE TESTS\n11.4\nThe hardware described in Section 11.2 was first tested in the laboratory by use\nof a signal from a waveform generator mixed with the output from a white noise source.\nThese measurements were designed to test the relative merits of the two techniques. (The\nusual method of evaluation (e.g., Sirmans and Bumgarner, 1975) is to define a Gaussian\nspectrum, add a noise spectrum, and then perform an inverse Fourier transform.) Signal\nand noise levels were measured for reference purposes with two identical receivers set to\nthe carrier frequency of 1250 Hz with a centered bandwidth of 300 Hz. These mixed signals\nthen served as inputs to the real and complex covariance pre-processor boards. Fifty 100-\nms samples were then obtained at frequency shifts of 0, 10, 30, and 60 Hz. Mean and\nstandard deviations were obtained by using the resulting frequency estimates. The results\nare shown in Figs. 11.3 and 11.4.\n65","ACOUSTIC DOPPLER DATA AVERAGED FOR\n20.0 MIN,\nSTARTING TIME\nWIND SPEED AND DIRECTION\nMONTH:\n6\nDAY:\n21\nPROFILES\nHOUR:\n3\nMIN:\n41\nWIND\nHEIGHT\nDIRECTION (D)\n(M)\nSPEED\nDIRECTION\n180\n270\n000\n090\n180\n(M/S)\n(DEG FM N)\n470.\n6.4\n205.\n*\nD\nS\n*\n450.\n7.0\n207.\n*\nD\nS\n*\n430.\n8.0\n209.\n*\nD\nS\n*\n410.\n8.3\n209.\n*\nD\nS\n*\n390.\n8.3\n207.\n*\nD\nS\n*\n370.\n7.2\n208.\n*\nD\nS\n*\n350.\n5.9\n210.\n*\nD\nS\n*\n330.\n4.2\n209.\n*\nD\nS\n*\n310.\n2.7\n202.\n*\nD\nS\n*\n290.\n1.5\n189.\n+D\nS\n+\n270.\n0.9\n171.\n*\nS\nD *\n250.\n0.5\n118.\n*S\nD\n*\n230.\n0.7\n32.\n* S\nD\n*\n210.\n1.2\n13.\n*\nS\nD\n*\n190.\n1.3\n11.\n*\nS\nD\n*\n170.\n1.3\n36.\n*\nS\nD\n*\n150.\n1.2\n41.\n*\nS\nD\n*\n130.\n1.4\n41.\n*\nS\nD\n*\n110.\n1.4\n38.\n*\nS\nD\n90.\n1.0\n24.\n+\nS\nD\n+\n70.\n1.3\n57.\n*\nS\nD\n50.\n2.4\n73.\n*\nS\nD\n0\n5\n10\n15\nWIND SPEED (M/S)\nFigure 11. 2. Sample output. Wind speed (S) uses scale along bottom of output in 0.25-m/s\nintervals.\nWind direction (D) uses scale along top of graph in 5° intervals.\n11.4.1\nConclusions\n11.4.1.1 Real covariance\nThe estimates described above were biased by noise with the magnitude\nof the error found to be a function of the magnitude of the frequency shift. Since the\nreal covariance utilizes a signal heterodyned to a frequency centered on 125 Hz, frac-\ntional errors in the frequency estimate provide a larger error in the estimate of the\ndifferential frequency shift.\n11.4.1.2 Complex covariance\n(1) The complex-covariance - technique showed results unbiased by white noise for a\nsufficiently large number of samples.\n(2) The standard deviation was a function of the signal-to-noise - ratio. The mean\nerror was also within 1/VN of the standard deviation with N samples.\n(3) With pure noise, the frequency estimate was biased towards zero-shift - because of\nthe centering and non -flatness of the filters.\n(4) Errors in the frequency estimates were independent of the magnitude of the\nfrequency shift from that of the carrier.\n66","60\n50\n40\n30\n20\nDoppler Shift From 1250 Hz\n60\n0\n10\n20\n30\n40\n50\n10\n14 dB\n0\n12 dB\n0\n9.5 dB\n-10\n-10\n6.0 dB\n-20\n-20\n-30\nNo Signal Input\nS/N = 0dd\n-30\n-40\n-50\n-40\n4.0\n5.0 (rms volts)\n0.0\n1.0\n2.0\n3.0\n14.0 (dB)\n0.0\n6.0\n9.5\n12.0\nS/N Ratio\nFigure 11.3 Real covariance error analy-\nComplex covariance error\nFigure 11. 4.\nsis showing error in Hz for given amount\nanalysis showing errors and standard\nof Doppler shift from carrier frequency\ndeviations of frequency estimates as\nof 1250 Hz, as a function of signal-to- -\na function of signal-to-noise ratio.\nnoise ratio (as defined in text.)\nConsequences for Field Measurements\n11.4.2\n(1) Under noisy conditions averaging times must be increased.\n(2) Wind variance measurements under windy (surface) conditions should be inspected\ncarefully since the background noise level increases with surface wind speed. Thus,\nalthough the variance might be expected to increase with wind speed and the data\nmight be observed to behave properly, such increases in the variance cannot neces-\nsarily be disassociated from S/N effects. However, for white noise, such variances\nin the frequency estimates will be equal to those obtained by using direct spectral\ntechniques (R. J. Keeler, personal communication).\nFIELD TESTS\n11.5\nThe results of the limited number of field tests to date have been encouraging.\nFollowing the construction of a prototype system during May 1979 we were able to obtain\nseveral nights of tower data with which to compare the new system's results. We found, at\nthat time, zero bias in the mean values averaged over the total data set of three nights\n67","and a mean difference in direction of 3 degrees. This system was then moved to a field\nsite and has been running since 4 July with about 95 percent data recovery to a height of\n600 m. A second device was then built several weeks before the BLIE experiment. During\ntesting some biasing was evident. Further inspection showed two sources of error. The\nfirst was the presence of other transmitting frequencies. We found that sufficiently\nstrong signals, although normally outside the bandwidth of our receiver, can pass through\nthe wings of the filter and be aliased into the estimate of the mean spectrum. The choice\nof a second operating frequency for backscatter sounding must, therefore, be made care-\nfully. A second source of error was the presence of nonwhite noise produced by the tower.\nWe analyzed the background noise with a real-time spectrum analyzer before, during, and\nafter data runs. With a delayed trigger, spectra were averaged for signals characteristic\nof the 300-m range gate. Figure 11.5 shows a typical spectrum obtained with winds from\nthe southwest greater than 4 m/s. Strong peaks in the noise are evident near 500 Hz and\nagain near our operating frequency of 1250 Hz. The peak in this latter region occurred\ntypically between 1100 and 1300 Hz, depending on conditions. We also calculated the\nerrors in our measurements as a function of wind direction; the results are shown in Fig.\n11.6. Underestimates are most prevalent with winds from the southwest. This is also the\ndirection toward which the carriage support on the tower is oriented. This support con-\nsists of two grids of 1000 elements each spaced 0.3048 m apart with an opening of 0.267 m.\nAt 25°C these dimensions correspond to acoustic frequencies of 1135 and 1297 Hz.\n11.6\nREFERENCES\nSirmans, D. and B. Bumgarner (1975): Numerical comparison of five mean frequency estima-\ntors. J. Appl. Meteorol. 14:991-1003.\nOwens, E. J. (1977) Microcomputer-controlled acoustic echo sounder. NOAA Tech. Memo. ERL\nWPL-21, NOAA/ERL, Boulder, Colo., 76 pp.\nNeff, W. D., and E. H. Brown (1979): Acoustic echo sounder operations during PHOENIX,\nChapter 14. In Project PHOENIX: The September 1978 Field Operation, W. H. Hooke\n(Ed.), NOAA/NCAR Boulder Atmospheric Observatory Rept. No. 1, available from NOAA/ERL,\nBoulder, Colo. 80303, and from NCAR Publications Office, Boulder, Colo. 80307.\nKaimal, J. C., and D. A. Haugen (1977): An acoustic Doppler sounder for measuring wind\nprofiles in the lower boundary layer. J. Appl. Meteorol. 16:1298-1305.\n68","Raw Echo\nBandpass Filtered Echo\nFigure 11.5. Spectrum analysis of\ntower noise in the range 0 to\n2500 Hz with a 6 m/s wind from\n2500 Hz\nthe south before and after band-\n0\npass filtering.\n0°\n4\nR\n3\nT2\n2\n1\n90°\n270°\nLight\nWind\nCases\nT1\nWSDop-WS Tow <0\nWSDop-WS Tow > 0\n180°\nFigure 11.6. . Error analysis of winds (in m/s) showing the dependence of the\nerrors on wind direction, which correlated with noise estimates made by\nspectral analysis.\n69","12. DOPPLER ACOUSTIC SYSTEM FOR WIND PROFILING (AVIT)\nPaul MacCready\nAeroVironment Inc.\nPasadena, California, U.S.A.\n12.1.\nINTRODUCTION\nThe AVIT (AeroVironment Invisible Tower) system is a pulse Doppler acoustic unit\ncontinuously monitoring air motions aloft (mean winds and turbulence). The system para-\nmeters have been chosen to provide all the atmospheric inputs for modeling the dispersion\nof atmospheric pollutants, on both research projects and operational programs. Considera-\ntions of economy, portability, simplicity of installation, reliability, and satisfactory\noperation in noisy environments are as important to the design as the basic accuracy and\nhigh-altitude capability.\nSince 1975, AeroVironment has developed and operated Doppler wind systems that\nuse various antenna beam configurations, several Doppler shift analysis methods, and\nnumerous transducer and enclosure designs. Before 1975 Ian Bourne at the University of\nMelbourne began development of high-altitude Doppler acoustic systems, with an emphasis on\nmonostatic configurations and a full spectrum analysis technique for ascertaining Doppler\nshift. A formal collaboration between AeroVironment (AV) and the University of Melbourne\nbegan in 1978; AVIT is the system that evolved from this collaboration. The basic algo-\nrithms and electronics concepts used in AVIT were developed by Bourne. At AeroVironment,\nJohn Worden has been in charge of the AVIT program. Bourne's early two-component mono-\nstatic system is described by Bourne and Brann (1978), who also give examples of observa-\ntions and comparisons with radiosonde data. Hopper (1978) briefly reviews the system and\nalso gives examples of measurements taken with it.\n12.2.\nTHE SYSTEM AND ITS PERFORMANCE\nAVIT is a flexible, modular system. The basic three-axis system uses three\nadjacent pencil-beam antennas. One tilts N (or S) 30° from the vertical to observe the\nN-S wind; one tilts E (or W) similarly to observe the E-W wind; and one points vertically\nto observe the vertical component. The antennas are operated sequentially, in the mono-\nstatic mode. Figure 12.1 shows a three-antenna array. Figure 12.2 shows a two-axis array\nmounted on a trailer.\nFigure 12.1. The three acoustic enclo-\nsures for the three-antenna system.\nEach contains a 1.8-m-diameter para-\nbolic reflector.\n70","Figure 12.2. Acoustic enclosures for\na two-antenna system mounted on a\ntrailer for easy portability. The en-\nclosures are oriented vertically for\ntransport. Parabolic reflector size\nis 1.2 m.\nA sound pulse (150 to 200 W) is transmitted at a frequency of 1500 Hz (2000 Hz\nalso available), with a duration of 180 ms for the tilted beams. The received echo is\nheterodyned and then processed through an electronic comb filter with 31 teeth, to yield\ncontinuously the full spectrum. For each 33.3-m (100-ft) altitude range gate, the spec-\ntrum is examined for acceptance or rejection, and then if accepted it is smoothed and\ncurve-fitted, and the resulting peak frequency and amplitude are stored. At the end of\nthe selected averaging period, say 20 min (variable from 5 to 30 min), the assemblage of\npeaks is explored by a number of histograms, spectra, and interpolation techniques, and\nthe best estimate of Doppler shift is ascertained along with an estimate of an observation\nreliability factor.\nThe resulting wind profiles for each period are printed out on a Texas Instru-\nments Silent 700 printer. In a three-axis system the display gives three components\n(vertical turbulence, and horizontal speed and direction) for every range gate, starting\nwith 67 m (200 ft) and continuing up to the maximum height selected (up to 47 range\ngates) or the maximum height observed. The data can also be recorded on digital tape.\nTwo other displays are available. One is a facsimile recorder giving a time\nplot of signal intensity vs. height. The signal intensity represents the strength of the\necho after initial processing by the comb filter, i.e., it shows only \"accepted\" range\ngates. Thus this recorder conveniently displays the overall height and quality of the\ndata.\nThe other display is an oscillograph showing the spectra in real-time sequence\nfor each range gate. It is a convenience when evaluating the contribution of ambient\nnoise to the echoes. Finally, a speaker is available to make the echoes audible and to\ngive the trained listener a good bit of information. Figure 12.3 shows a version of the\ncomplete data processing and display system. (Only item missing is the oscillograph.)\nThe velocity component range is +15 m/s, limited by comb filter width. An\nautomatic frequency alteration for the transmit pulse can be selected by the operator.\nThen, on the basis of the wind measurements during the preceding integration period the\nfrequency is adjusted for the next period to keep the comb filter operating in its middle\nrange. This extends the working range of the filter to component speeds of +25 m/s, and\nso in some directions wind speed can be covered to vector speeds of 35 m/s. This tech-\nnique permits the total frequency band evaluated to be narrow and minimizes spurious noise\nacceptance.\nSpeeds are printed out to 0.1 m/s resolution, and directions to 3° resolution.\nNominal reproducibility during periods of strong signals is deemed to be about 0.2 m/s,\nalthough examination of data runs often shows consistency between range gates to be within\n0.1 m/s and 3°.\n71","MODEL\nCHART RECORDER\nFigure 12.3. AVIT data processing and\ndisplay system in operation, with\ndigital tape recording as well as\ndata printout and facsimile display.\nThe maximum altitudes at which data are obtained vary widely with meteorological\nconditions. An estimate from all operations with AVIT in Australia and the United States\nover the last year indicates that the 95% and 5% data recovery percentiles correspond to\n300 m and 1000 m, with percent vs. altitude varying linearly between these heights.\nThe clock has battery backup to maintain time accuracy during power outages.\nThe system features automatic restart after power failure. It is also designed for unat-\ntended operation.\n12.3.\nOUTPUTS\nFigure 12.4 presents a typical printout on the Texas Instruments Silent 700\nprinter. This is a 20-min interval display. The time during which data were taken is\nindicated at the top of the printout (date code, time 0622:02 to 0640:21). The left\ncolumn gives height in units of 33.3 m (Range 2 = 66.7 m, Range 3 = 100 m, Range 9 =\n300 m, etc. ) . Range 1 is omitted in this long-pulse, high-altitude version because there\nis insufficient time for the high-output driver to recover completely from its transmit\npower pulse before serving as the receiver transducer. Range 0 is an option not included\nin this example; it gives the near-surface wind component information from two propeller\nanemometers mounted on a 10-m mast.) )\nThe numbers across the top give instrument operating codes and automatic gain\ncontrol (AGC) levels. The columns from left to right are as follows:\nHT\nHeight ranges in units of 33.3 m\nNS\nThe N-S component (+ from N; m/s)\nR\nData reliability assessment for this component (0 is best, 9 is worst;\ndata from 0 to 7 are generally deemed suitable for meteorological\napplication).\nNO\nNumber of pulses utilized in deriving N-S component.\nEW\nThe E-W component (+ from E).\n72","START TIME= 0019\n06\n22\n02\nEND TIME=\n0019\n06\n40\n21\n28\n1\n1\n24\n0\n0\n70\n86\n69\nHT\nNS R NO\nEW\nR NO\nVERT R\nNO\nSD\nVEL\nANG\nR\nNO\n32\n-2.7 3 34\n-6.1 0 34\n0. 0 1\n34\n0.3\n6.6\n246\n3\n34\n31\n-2.8 3 31\n-5.4 0 32\n0.2 1\n26\n0.3\n6.0\n243\n3\n31\n30\n-3,7 1 29\n-4.3 3 28\n0.2 0\n23\n0.3\n5.7\n228\n3\n28\n29\n-4.2 0 33\n-3.9 0 30\n0.2\n0\n25\n0.3\n5.8\n225\n0\n31\n28\n-4.5 2 33\n-3.6 1 28\n-0.0 1 30 0.4\n5.8\n219\n2\n30\n27\n-4.5 1 33\n-2.1 0 32\n-0.1 2 27 0.4\n5.0\n204\n1\n32\n26\n-4.7 2 30\n-1.4 0 31\n0.0 3\n28\n0.3\n4.9\n195\n2\n30\n25\n-5.3 5 33\n-0.7 1 28\n0.0 1\n31\n0.2\n5.2\n186\n5\n30\n24\n-5.8 2 34\n-0.4 0 33\n0.2 5\n32 0.2\n5.8\n183\n2\n33\n23\n-6.2 0 33\n0.3 0 34\n0.1 3\n34 0.1\n6.1\n177\n0\n33\n22\n-6.2 0 34\n0.2 0 33\n0.0 4\n34 0.4\n6.2\n180\n0\n33\n21\n-6.1 0 34\n0.3 0 33\n0.0 1\n34 0.1\n6.1\n177\n0\n33\n20\n-5.9 0 34\n0.2 0 34\n0.0 2\n32 0.2\n6.0\n180\n0\n34\n19\n-5.8 0 34\n-0.2 0 34\n-0.0 4\n34\n0.3\n5.8\n180\n0\n34\n18\n-5.6 4 34\n-0.8 1 34\n0.2 4\n34 0.3\n5.6\n186\n4\n34\n17\n-5.4 0 34\n-1.9 0 34\n0.2 4\n34 0.2\n5.7\n198\n0\n34\n16\n-5.3 0 34\n-2.0 0 34\n0.1 4\n34 0.3\n5.7\n201\n0\n34\n15\n-5.3 0 34\n-1.1 2 34\n0,0 4\n33 0.1\n5.4\n192\n2\n34\n14\n-5.3 0 34\n-0.2 0 34\n0.2 7\n33 0.2\n5.3\n180\n0\n34\n13\n-5.6 2 34\n0.1 0 34\n0.1 5\n33 0.1\n5.6\n180\n2\n34\n12\n-6.5 3 34\n0.0 0 34\n0.0 4\n32 0.1\n6.4\n180\n3\n34\n11\n-6.9 0 34\n0.2 0 34\n0.1 6\n34 0.2\n6.9\n180\n0\n34\n10\n-7.3 0 34\n0.2 0 34\n0.1 6\n34 0.1\n7.2\n180\n0\n34\n9\n-7.4 1 34\n0.4 0 34\n0.0 4\n34 0.0\n7.3\n177\n1\n34\nS\n-7.4 1 34\n0.5 3 34\n0.1 4\n34 0.1\n7.4\n177\n3\n34\n34\n7\n-7.6 2 34\n0.4 0 34\n0.1 7\n34 0.1\n7.5\n177\n2\n34\n0.1\n7.6\n177\n2\n34\n6\n-7.6 2 34\n0.5 0 34\n0.1 7\n0.1\n7.5\n177\n5\n34\n5\n-7.6 5 34\n0.5 0 34\n0.1 5\n33\n0.1 5\n34\n0.1\n7.3\n174\n3\n34\n4\n-7.3 1 34\n0.8 3 34\n174\n0\n34\n3\n-6.9 0 34\n0.8 0 34\n0.1 7\n34\n0.1\n7.0\n-0.1 2\n13\n0.4\n6.8\n177\n2\n33\n2\n-6.8 0 34\n0.5 2 33\nFigure 12.4. Sample data printout of AVIT system.\nData reliability assessment for E-W component.\nR\nNumber of pulses utilized in deriving this component.\nNO\nVertical wind (+ denotes upcurrent)\nVERT\nData reliability assessment for vertical component.\nR\nNumber of pulses utilized in deriving vertical wind.\nNO\nStandard deviation of vertical wind (calculated with\nSD\nrespect to zero vertical wind).\nTotal horizontal wind speed (m/s).\nVEL\nHorizontal wind direction (degrees)\nANG\nData reliability assessment for speed and direction.\nR\nNumber of pulses utilized in deriving speed and direction.\nNO\nThe operator commands a wide variety of printout options. Figure 12.4 repre-\nsents a common selection for operational uses, the main variations being different alti-\ntudes (the lower the altitudes, the faster the pulse repetition rate and so the greater\n73","the amount of information available for processing); longer or shorter averaging times;\nand, for the two-component system, omitting the vertical component.\nIn the example given, the horizontal data (components, speed, and direction) are\nderived from the horizontal components only. Since the vertical velocity averaged over 20\nmin is usually small, even in convective conditions, the error in omitting the vertical\nvelocity correction is also usually small. The correction involves taking 1.73 times the\nvertical component, adding that to the N-S component and subtracting that from the E-W\ncomponent (for the N-pointing and W-pointing antenna orientation employed in this example)\nto correct the components and hence the speed and direction. This correction can be\nselected in the computer and then the speed and direction printouts are for the corrected\ndata. If the vertical velocity data observation is missing at that height, or has a bad\nreliability assessment number, the correction computation can assume a zero vertical\nvelocity.\nFor research purposes, the operator can choose to print out more information.\nThe integrated full spectra for each component can be printed. Alternatively, the display\nwill give the components calculated from each of six different histograms or spectra or\ncombined analysis approaches. It is the agreement between these component estimates, plus\na weighting depending on the number of pulses selected, that is used to derive the relia-\nbility assessment quantity. A combination of a specific histogram and spectrum were\nused to obtain the numbers presented in Fig. 12.4.\nThe output can also be recorded on tape. We have used a Texas Instruments\nSilent 700 ASR cassette recorder for recording the results of each 20-min run, essentially\nthe data illustrated in Fig. 12.4. We also use a Kennedy 1600 digital tape machine to\nrecord the integrated data and, if desired, to record fully every spectrum tooth output\nfor every range gate for every pulse. This second option yields basic data for research\non improving the algorithms for data selection and for exploring alternative methods of\nderiving turbulence from the echoes.\n12.4.\nMAIN FEATURES\nThe primary design options of a pulse Doppler acoustic system are (1) overall\nbeam configuration, (2) transducer/antenna characteristics, and (3) the Doppler shift\nprocessing technique. (Features such as pulse generation, preamplifier, and data display,\nare not significant in differentiating systems.) For AVIT, the design choices are as\nfollows:\n(1) The overall beam configuration is monostatic. There is also a narrow angle\nbistatic variation available for special tasks.\n(2) The transducer/antenna system uses horn-driver-reflector-enclosure geometry and\nmaterials tailored from theory and considerable experimentation. In addition, a\nspecial treatment of the enclosure edges lessens diffraction at these edges, cuts\nsidelobes substantially, and makes the system suitable for use in noisy or urban\nlocations.\n(3) Doppler shift for each pulse and range gate is ascertained in real time by a\ncontinuous full-spectrum technique coupled with versatile data selection/rejection\ncriteria (and the data quality assessment factor is one of the system outputs)\nThe following sections explore the rationale behind the first two design choices.\nThe Doppler shift subject has already been treated briefly in previous sections. Suffice\nit to note here that the analog filter teeth (4.3 Hz wide) are both economical and stable;\nthat the comb filter method substitutes for the more conventional full spectrum method,\nthe digital FFT, while decreasing the demands on the computer; and that the comb filter\nmethod automatically weights the information in the previous range gate and adds it, to\nyield more significant information than that which can be derived solely by FFT examina-\ntion of echoes from a single range gate.\n74","12.4.1\nOverall Beam Configuration\nIn comparison with a bistatic beam configuration, the monostatic system offers\nseveral distinct advantages:\n(1) The antennas can be located adjacent to each other (even all on a single trailer)\nfor convenience of installation.\n(2) The tilted monostatic antenna senses the same percentage of the horizontal wind\nat all heights. This is simpler than the bistatic case, which involves altered\ngeometry at each range gate, and which has very strong sensitivity to vertical com-\nponents at the high range gates.\n(3) Only pencil-beam antennas are used in the typical monostatic system, while fan\nbeams are used in bistatic systems. The broad fan beams have poorer sidelobe suppres-\nsion, even when used with complex enclosures. When used for receiving, the fan beams\nare relatively inefficient in keeping out noise from low elevation angles; when used\nfor transmitting, they can be disturbing to persons nearby.\n(4) Tilted beams can be tilted away from noise sources, to minimize interference.\nThere is one significant disadvantage to the monostatic system. It operates on\nechoes scattered only at 180°, and such scattering comes only from the temperature micro-\nstructure field. The bistatic systems utilize echoes from both the velocity and tempera-\nture fields. With moderate turbulence but near-neutral stability, one would expect mono-\nstatic scattering to be weak whereas bistatic scattering would be strong. Another disad-\nvantage, but one which is generally insignificant, is that the sensed volumes at a given\nheight are not at exactly the same location. This is of little concern when data are\naveraged over a few minutes, since the data are then deemed representations of an air\nvolume large in horizontal extent.\nIt turns out that in virtually all conditions the monostatic approach is practi-\ncal because the high efficiency inherent in having the transmit and receive beams line up\nexactly compensates partially for the weaker scattering cross section. Thus the main\ndisadvantage of the monostatic system is not overwhelming; one can use the system and\nbenefit from its good features. The average altitudes reached (see Section 12.2) demon-\nstrate the general suitability of the technique. At night, with stability aloft, partic-\nularly in complex terrain, there are good monostatic signals at 500 m even with very light\nturbulence (less than E .1/3 = 0.5 cm2/3 -1 where E is the dissipation rate). The worst\nperiod for monostatic echoes (and bistatic) is typically in weak pressure gradient condi-\ntions in late afternoon when solar heating shuts off, heat flux up into the atmosphere\nstops, the lapse rate remains close to neutral, and the turbulence dissipates. To cover\nthis period we have tested an approach that merges the bistatic method with a monostatic\nsystem.\n12.4.2\nAntenna Systems\nAVIT employs a standard driver feeding downward into a tuned horn, spreading\nsound out to a parabolic reflector from which pencil beam is emitted upward. The assem-\nbly is housed in a large acoustic enclosure that decreases the sidelobes for transmitting\nor receiving. The research instrument configuration uses a 1.8-m reflector, and a parallel-\nsided enclosure built of six sheets of 1.2-m by 2.4-m plywood or chip board. The enclo-\nsure is lined with 5-cm-thick glass wool for sound absorption. The glass wool is used\ninstead of plastic foam because rain water drains better with the wool. The parabolic\nreflector can be heated for snow removal.\nThe two-component portable instrument version uses 1.2-m reflectors in five-\nsided enclosures, with both enclosures optionally mounted on a trailer for easy portabil-\nity. During transit the enclosures are set upright. They are then set up for operation\nby tilting 30° from vertical in the N and W directions (or other orthogonal orientation).\n75","The top edges of the enclosure are equipped with Thanadners, at Lockheed Co.\nThanadners are teeth, here 0.6 m high and 0.1 m wide, covered on both sides with absorbing\nmaterial, which have the effect of acoustically \"feathering\" the top edges and greatly\ndecreasing diffraction. Our tests have shown the additional sidelobe suppressions at low\nangles to be as much as 12-14 dB. The amount will depend greatly on the sidelobes ini-\ntially present, and on whether or not the wall attenuation is adequate. The Thanadners\nhelp make the acoustic system suitable for operation in urban environments.\nThe wind speed at which wind noise becomes a problem has not been determined for\nthese enclosures, either with or without Thanadners. On several installations we worried\nabout possible wind noise, but avoided the problem by erecting a fence upwind.\n12.5.\nTHE FUTURE\nAVIT is satisfactory as a high-altitude remote probe for many purposes, but\nimprovements are always desirable. Work will continue in order to reach higher altitudes\nor to cover a given altitude a larger percentage of the time. The main approaches are to\nincrease power and to apply more sophisticated algorithms for extracting valid Doppler\nshift information when the signal/noise ratio is low. Work will also continue to obtain\nadditional turbulence parameters, and to validate the observations by aircraft measure-\nments.\nOur goal is to have an instrument that provides all the meteorological inputs\nneeded to supply a rational diffusion model covering a wide range of conditions. Wind and\nturbulence profiles are obviously essential inputs. Temperature gradients are needed only\nto assist in calculating plume rise, and they need not be precise; the standard plume rise\nequation can use only a few broad categories, such as unstable, neutral, stable, and very\nstable. It may prove possible in many cases to derive such categories from the profiles\nof wind and turbulence.\n12.6.\nREFERENCES\nBourne, I. A., and H. N. Brann (1978): AIRMET Conf. R. Met. Soc. (Aust. ), , Bureau of\nMeteorology, Melbourne, Australia.\nHopper, V. D. (1978) : Acoustic sounding of the atmosphere. Endeavour (new series) 2:121.\n76","13. RADIAN CORPORATION MODEL 800 ECHOSONDE\nM. A. McAnally\nRadian Corporation\nAustin, Texas, U.S.A.\n13.1\nINTRODUCTION\nThe Doppler acoustic sounding system is used to characterize the thermal struc-\nture and wind profiles in the lower atmosphere (below 1 km) Transmitted acoustic tones\nare scattered by the turbulent atmosphere. The strength of the direct backscatter depends\non the temperature fluctuations in the scattering volume. The frequency of the scattered\nenergy is shifted by an amount dependent on the motion of the scattering volume. There-\nfore the returned echo strength as a function of time provides information about the\nthermal structure as a function of altitude. The mean Doppler frequency shift is propor-\ntional to the average velocity of the scattering volume along a line that bisects the\ntransmit and receive beams. By measuring the mean Doppler frequency shift in three inde-\npendent directions, the three wind components can be determined as a function of altitude.\nOnly recently with the availability of low-cost digital systems has it been possible to\nestimate the Doppler frequency shift in a cost-effective system. Radian's Model 800\nDoppler Echosonde utilizes the LSI-11 microcomputer to perform complex covariant process-\ning to measure the Doppler frequency shift of the returned echo.\nThe Radian Echosonde system comprises five basic subsystems:\n(1) Acoustic antenna and transducer assembly.\n(2) Acoustic noise suppression (Septacuff).\n(3) Bistatic transmit horn.\n(4) Microcomputer and control electronics.\n(5) Display terminal.\n13.2\nACOUSTIC ANTENNA ASSEMBLY\nThe antenna assembly consists of an exponential horn and transducer which di-\nrects acoustic energy into a parabolic reflector to form a 10° acoustic beam. Because of\nthe high magnetic field strength in the compression driver coil gap, the assembly also\nfunctions well as a return echo detector. The electrical signal from the compression\ndriver-detector is amplified at the antenna to minimize electrical noise effects on the\nreceiver system.\nThe transmitted tone is 2000 Hz in the standard configuration; however, other\nfrequencies have been used. The transmitted tone power is 150-W electric input power with\na selectable pulse duration of 0 to 990 ms in 10-ms steps. The pulse repetition rate is\nalso selectable from 1 to 99 S in 1-s steps. The pulse duration is the controlling vari-\nable for altitude resolution, and the repetition rate sets the maximum travel time, and\nthus the maximum altitude.\n13.3\nACOUSTIC NOISE SUPPRESSION\nThe acoustic enclosure design, based on theoretical and experimental studies by\nthe NOAA Wave Propagation Laboratory, isolates the receiving antenna from ground-based\n77","interfering noise sources. The fully portable Septacuff is constructed of seven sides and\na bottom, all of which are lined with acoustic foam and a sandwiched lead sheet septum for\nmaximum sound control. The Septacuff shape was selected to minimize diffracted ground-\nlevel noise. The sides of the enclosure are flared away from the 1.2-m parabolic antenna/\nreflector at the bottom. The total weight of the enclosure is 250 kg (550 1b); it can be\ndisassembled down to parts that weigh less than 50 kg (110 1b).\n13.4\nBISTATIC TRANSMIT HORN\nThe bistatic exponential transmit horn is constructed of fiberglass and shaped\nto form a broad vertical beam to provide information over a range of altitudes. The\nbistatic transmitter uses the same type of transducer as the monostatic antenna assembly.\nThe transmitter provides a fan-shaped beam with 50° vertical beamwidth, and 10° horizontal\nwidth.\n13.5\nMICROCOMPUTER AND CONTROL ELECTRONICS\nThis subsystem consists of a microcomputer, amplifiers and filters, controls,\nand power supply. The central processing unit is a Digital Equipment Corporation LSI-11\nwith 4-K memory and hardware multiply/divide Because the control program resides in\nprogrammable read-only memory (PROM), the system will automatically restart after power\nfailure. The Echosonde signal-generating and processing electronics are assembled on\nprinted circuit boards designed for plug compatibility with the LSI-11 microcomputer. The\nmodular system design provides many optional system configurations by exchanging or adding\ncircuit boards. For example, a user may select the option that provides only single axis\nmeasurement, i.e., only the vertical wind components and temperature structure, and up-\ngrade to a full three-axis system by adding the bistatic transmitters, and changing the\nPROM board, which contains the system software.\n13.6\nDISPLAY TERMINAL\nThe display unit is a dot-matrix digitally controlled line printer. The printer\nhas a special optical shading character set for displaying the intensity of the back-\nscatter return. Figure 13.1 shows a sample of the display terminal output. The standard\nalpha-numeric character set is used to print the wind data determined by the Doppler\nfrequency shift. The figure shows horizontal wind speed (tenths of m/s), horizontal\ndirection (degrees east of north), vertical and horizontal wind direction variance (de-\ngrees), and a vertical wind indicator. The display can also provide an estimate of the\nreturned signal-to-noise ratio.\n13.7\nOPTIONS\nIn addition to the basic subsystems, the Echosonde system offers the following\noptional features:\n(1) 220 V a.c., 50-Hz - input power.\n(2) Telecommunications (serial ASCII) over two-wire or standard telephone with\nstandard modems.\n(3) Optional peripheral storage units including 9-track magnetic tape, cassette tape,\ndisk, or paper tape.\n(4) Heated antenna/reflector.\n(5) Tilting base for Septacuff.\n78","Be's\n18\n21\n147#\n31\n141\n22\n147+\nT23*\n132*\n18\n123*\n18\n138#\n21\n27\n123*\n28\n120*\n21\n129#\n19\n129#\n20\n7/16 4:50\n10#\n22\n2\n3\n2\n13\n2\n8\n3\n1\n20\n17.\n1\n-E\n-6\nB\nD\nSPEED\n9\nDIR\n75\nTEMP 222\nFLUX\n0\n-F\n-G\n7\n18\n1\n04\n22\n-D\n-\n-D\nC\nC.\n22\n24\n141*\n22\n129*\n210*\n17\n210*\n150#\n7/16\n5: 0\n7.8\n21\n12\n2\n20\n46\nA\nA\nE\nSPEED\n12\nDIR\n66\nTEMP 222\nFLUX\no\nA\nA\nC\nA\n-0\n-E\n26\n11\n5\n19\n3\nt\n18\n3\n26\nA.\nB\nD\nA\nE\nC\nB\nA\n7\n264*\n20\n285\n1\n2\n129*\n19\n147*\n21\n144*\n23\n141#\n21\n156*\n24\n141*\n6\n210*\n7/16 5:10\n162*\n17\n27\n3..\n23\n3\n19\n5\n22\nB\nE\n6\nG\nSPEED\n8\nDIR\n57\nTEMP 220\nFLUX\no\nA\n15\nFigure 13.1. Sample format of display from printer.\nSYSTEM CONFIGURATION OPTIONS\n13.8\nThe optimum acoustic sounder configuration is dependent on the specific require-\nments of the application. The user of the acoustic sounder system must consider the\nfollowing:\n(1) Altitude range required.\n(2) Sampling interval required.\n(3) Noise interference as well as potential noise nuisance.\nRadian's Model 800 Doppler Echosonde can be configured in a variety of ways\ntailored to each specific application. All configurations determine thermal structure and\ndisplay on the line printer, but the user may elect to record the following:\n(1) Single-axis (vertical) wind component.\n(2) Two-axis (vertical and one horizontal) wind components.\n79","go\n10°\n90°\ntilt\n90°\nPlan view\nPlan view\nBistatic\nMonostatic\ntransmit\ntransmit/receive\n90°\n90°\n10°\nMonostatic\nMonostatic\ntilt\ntransmit/receive\ntransmit/receive\nBistatic\nMonostatic\ntransmit\ntransmit receive\n(a)\n(b)\nFigure 13.2. Optional three-axis (u, V, w) configurations for the Model 800\nDoppler Echosonde: a) bistatic, , b) monostatic.\n(3) Three-axis (vertical plus orthogonal horizontal) wind components.\nFigure 13.2 illustrates two choices for arranging the transmit/receive antennas\nto record wind components. The bistatic arrangement separates the transmit and receive\nantennas for resolving the horizontal wind components. This arrangement provides the\nsimplicity of receiving all returned echoes at one receiver. The monostatic arrangement\nprovides one to three transmit/receive modules complete with acoustic enclosure. Two of\nthe acoustic enclosures are tilted to obtain the horizontal wind components. The monosta-\ntic arrangement has the advantage of directional focusing of the transmitted acoustic\nenergy.\n13.9\nCALIBRATION VERIFICATION\nThe Model 800 Echosonde normally requires no field calibration after installa-\ntion. The instrument is fully calibrated and tested prior to shipment. It is usually\nadvantageous, however, to verify several critical aspects of the Echosonde operation\nfollowing a field installation. The sound level of each of the acoustic transmitters is\nnormally checked after installation. The sound level of each bistatic transmitter should\nbe 133 dB relative to 20 uN/m². The monostatic transmitter sound level should be 128-130\ndB relative to 20 uN/m2 The preamplifier d.c. offset is also normally checked after\ninstallation. This is accomplished by injecting a 100-V signal into the preamplifier\nand adjusting the zero trim pots for less than 1-mV offset voltage. The remaining analog\nadjustments are not usually possible in the field without the use of specialized equipment.\n80","14. SWEDISH SODAR SYSTEM\nSören Salomonsson\nDepartment of Meteorology\nUniversity of Uppsala\nUppsala, Sweden\nMats Hurtig\nSensitron AB\nStockholm, Sweden\nINTRODUCTION\n14.1\nDuring the period 1970-1975 - a monostatic acoustic sounding system was developed\nat the Swedish Research Institute of National Defence under the leadership of Hans Ottersten.\nThis sodar system was then utilized in research projects in Sweden and other European\ncountries (Ottersten and Eklund, 1973; Ottersten et al.. , 1974; Ottersten, 1975a and 1975b).\nStarting in 1975, the Swedish sodar system was further developed in joint projects\nbetween the Department of Meteorology of the University of Uppsala and the electronic\ncompany Sensitron AB of Stockholm (Holmgren et al. , 1976). A new monostatic Doppler system\nwas built in 1976 by applying a phase-locked loop (PLL) circuit for tracking the frequency\nshift of the return signal. The sodar project is supported by the Swedish Board for Space\nActivities and the Swedish Board of Technical Development.\nA first application of the Doppler unit was done in cooperation with the Swedish\nMeteorological and Hydrological Institute in a boundary layer study during the first two\nweeks of May 1977. The vertical wind velocity was derived from the Doppler shift at 100,\n175, 250, and 350 m at some brief periods. Figure 14.1 shows a set of these measurements.\nm/s\n0.4\nLEVEL\n350 m\n0.2\n0\n-0.2\nx\n-0.4\nLEVEL\n0.4\n250 m\nX\n0.2\n0\n-0.2\n-0.4\n0.4\nLEVEL\n175m\n0.2\n0\n-0.2\n-0.4\nLEVEL\n0.4\n100 m\nX\n0.2\n0\n-0.2\nLOCAL TIME\n-0.4\n57.50\n58.00\n57.10\n57.20\n57.30\n57.40\n10.56.40\n56.50\n57.00\nFigure 14.1. Vertical wind velocities derived from the acoustic\nDoppler measurements for different heights on 5 May 1977.\n81","WIND VELOCITY (m/s)\n8\n7\n6\nX\n5\nX\n4\n3\n2\n1\nLOCAL TIME\n12.21\n13.01\n14.01\n250\nX\nx\nWIND DIRECTION (degrees)\nx\nX\n240\nX\n230\n220\n210\n200\n190\nLOCAL TIME\n180\n12.21 25 29 33 37 41 45 49 53 57 13.01 05 09 13 17 21 25 29 33 37 41 45 49 53 5714.01\nFigure 14.2. Example of the horizontal wind velocity and wind directions\nmeasured by Doppler (solid line) and pibal tracking (crosses) at a height\nof 60 m. Each data point is centered on the corresponding 2-min averaging\ninterval.\nA preliminary description of the sodar measurements obtained during this field project is\ngiven in Salomonsson and Ivarsson (1978)\nMeasurements of the horizontal wind velocity were carried out during the autumn\nof 1978 for the benefit of a project that aimed at finding the best location for a wind\npower station in the area. Two monostatic sodar systems, with tilted antennas, were used\nto determine the horizontal wind components. The derived wind velocity was compared with\nsimultaneous wind measurements obtained from double theodolite pibal trackings. An example\nof these measurements is shown in Fig. 14.2.\n14.2\nTECHNICAL DESCRIPTION\nThe monostatic system used at the intercomparison in Boulder is a commercial\nsystem manufactured by Sensitron AB. It consists of two antennas for measuring the two\nhorizontal wind components. Figure 14.3 shows the relationships of the parts of the system.\nTable 14.1 lists the specifications. The system uses two antennas, but a third antenna can\nbe added to measure the vertical wind velocity. The antennas can be clustered together,\nwith the tilting antennas pointing out from the central point along the orthogonal planes,\nor they can be separated as shown in Fig. 14.4. The antennas are fed by compressor drivers\nof 100 W. They give an acoustic beam pattern like that in Fig. 14.5.\n14.2.1\nDescription of the Monostatic System\nDuring transmission, a tone-burst is generated in the transceiver unit SR 20 by\nthe combined band-pass filter and tone generator. The tone-burst is fed through a power\namplifier to the transducer of one of the selected antenna channels. The received echo\nsignals are amplified in the preamplifier and transferred by balanced cables to the receiver\nin the transceiver unit SR 20.\n82","Antenna Units SR 40\nInterface\nSR 90\nDigital Tape\nTransceiver Unit SR 20\nRecorder SR 36\nSignal/\nDoppler\nA/D\nNoise\nUnit\nConverter\nAnalyzer\nPLL\nTape\nSwitchbox SR 80\nDriver\nBP Filter\nT/R\nPre-\nHigh-Pass\nAC\n1/R\nand\nDetector\nI/0\nSwitch\namplifier\nFilter\nAmplifier\nAmplifier\nTone Gen.\nPower\nControl\nLog.\nComputer\nRamp\nAmplifier\nUnit\namplifier\n8080\nChart\nColor\nRecorder\nDisplay\nSR 32\nSR 34\nKeyboard\nFigure 14.3. Block diagram of the acoustic Doppler sounder.\nThe echo signals are high-pass filtered to eliminate high energy components of\nthe background noise at frequencies below 800 Hz. A linear-gain amplifier is used to\ncompensate for spherical divergence of the scattered acoustic wave. The PLL circuit gives\nan output signal proportional to the Doppler shift of the incoming signal. To reduce\nnoise the echo signals are passed through a signal-to-noise analyzer, which selects\nsignals that have a given ratio to the background noise level. The detected Doppler\nsignal is connected by the interface SR 90 to the microprocessor in the tape recorder unit\nSR 36 for determination of the wind vector. The other channel works in exactly the same\nway. The wind information received and processed by the microprocessor is presented on\nthe color display SR 34 (Thomson and Scheib, 1978)\nThe intensity for the temperature fluctuation received at one of the antennas is\nband-pass filtered and detected. The signals are processed and presented on the color\ndisplay SR 34. Even chart recorder SR 32 presents temperature fluctuation and is fed by\na\nlog amplifier, which compensates for the difference in the dynamic range of the detected\nsignal to the recorder.\n14.2.2\nData Presentation\nThe color display SR 34 is an eight-color CRT screen that contains a micro-\nprocessor for the color representation. The wind information is presented on the screen in\ndifferent pictures which can be selected from the keyboard. Profiles of wind speed and\ndirection, columns of wind speed and direction, and a combination of wind speed and the\nintensity of the temperature fluctuation can be displayed. The intensity of the tempera-\nture fluctuations is classified in five colors and presented in a height/time diagram.\nIntegration time of data, color representation, program start-up, etc., can be controlled\nfrom the keyboard.\n83","Table 14.1. Technical specifications of the Swedish sodar system\nEquipment\nSpecifications\nAntennas (two)\nParabolic dish\nFiberglass\nDiameter: 1.2 m\nTransducer\nAltec Lansing 291-16B\nTransceiver SR 20\nTransmitter\nFrequency: 2,400 Hz (1,800 Hz)\nPulse power: 100 W\nPulse width: 30, 90, 180 ms\nPulse repetition rate: 0.1 - 0.2 Hz\nReceiver\nBalanced input: 600 52\nHigh pass filter 800 Hz\nRange correction: 1/R within height range 20-1,000 m\nBandwidth: 20, 40, 80 Hz (for recorder SR 32)\nSounding range: 20-1,500 m\nPRE\nPRE\nAMP.\nAMP.\nTRANSCEIVER\nTRANSCEIVER\nA\nB\nTHREE CHANNEL\nWIND PROCES\nTRIG DELAY\nWIND PROCES-\nTHREE CHANNEL\n4\nA\nRECORDER\nSING UNIT\nUNIT\nSING UNIT\nRECORDER\nSODAR\nRECORDER\nN\nSODAR A\nSODAR B\nFigure 14.4. Block diagram of the monostatic Doppler system used in the pro-\nject on Gotland and the horizontal orientation of the two antennas (A and B)\nin relation to the north axis.\n84","0 5° 10°\n20°\n30°\n-10\n40°\n50°\n-20\n60°\n-30\n70°\n-40\n80°\n90°\nFigure 14.5. Polar pattern of the acoustic\nbeam for the transmitting antenna at\n2,400 Hz. (The lobe width is about 8°.)\nAll data are recorded on tape in data blocks. Every block contains number of\nday, time, wind information, and intensity of the temperature fluctuations for one sounding\ninterval.\nAnother presentation unit is recorder SR 32 which gives the intensity of the\ntemperature fluctuation along one axis. Recorder SR 32 works on a new principle, present-\ning grey shades on metallized paper. This recorder is almost free of maintenance compared\nwith earlier recorders.\n14.3\nEXAMPLES OF DOPPLER MEASUREMENTS\nFigure 14.1 shows graphs of vertical wind velocities derived from the Doppler\nshift at four selected levels obtained in an atmosphere of a slightly stable thermal strat-\nification. It may be noted that the measuring period is only about 1.5 min. Therefore, a\ndiscussion of average wind velocities has no significance in this case. During ideal\nconditions one may expect to get zero mean vertical velocity if the averaging interval is\nlong enough (Kaimal and Haugen, 1977). Variations in the vertical velocities indicate a\n\"wavy\" pattern with a tendency for crests and troughs to coincide at the four levels. In\norder to discuss the vertical wind structure in detail a much longer time series is needed.\nDuring the autumn of 1978 an extensive project aimed at finding the best location\nfor a wind power station was carried out in selected high-wind areas on the Swedish island\nGotland (Smedman-Högström and Faxén, 1980). In connection with this wind-prospecting\nproject, supported by the Swedish National Board for Energy Source Development, two mono-\nstatic sodar systems were used. The sodar measurements were carried out in a joint project\nbetween the Department of Meteorology of the University of Uppsala and the Swedish Meteor-\nological and Hydrological Institute, with technical support by Sensitron AB.\nA simplified block diagram of the two monostatic sodar systems (A and B) used in\nthe wind-prospecting project is shown in Fig. 14.4. The system was built around two stand-\nard sodar units. The Doppler frequency received at each antenna was analyzed in the wind-\nprocessing unit and presented on the analog 3-channel recorder. The two sodar systems\noperated at the same frequency (2.4 kHz). To avoid interference between the two systems\neach transmitter was pulsed separately in time by the trigger delay unit, with a pulse\nrepetition frequency of 0.25 s-1. The antennas were tilted 50 degrees from the horizontal\nplane, with the intersection of the antenna beams at a height of 60 m.\nThe radial velocities were derived from the 3-channel recorders. By using the\nassumption of a zero mean vertical velocity for the time-averaging interval and trigonomet-\nric relationships the horizontal wind vector was computed. Figure 14.2 shows a preliminary\n85","result of the horizontal wind measurements. The wind velocity derived from the Doppler\nshift was then compared with simultaneous wind measurements from double theodolite pibal\ntrackings (Alexandersson and Bergstrom, 1979).\nWind velocities show satisfactory agreement, but the wind directions show more\ndifferences. These differences could probably be explained to some extent by considering\nthe uncertainties in the determination of the Doppler shift (Beran and Clifford, 1972) A\nsmall error in the determination of the Doppler frequency in one or both of the components\naffects the wind direction more than the wind velocity. Another reason for the discrepancy\nis that in general the actual position of the balloon does not coincide with the intersec-\ntion of the antenna beams. Furthermore, the vertical wind velocity will also influence the\nmeasurements, especially when the averaging period is not long enough to make the mean\nvertical component negligible.\nA more detailed analysis of the whole series of tests of the Doppler measurements\nfrom the wind-prospecting project will be published in the series of reports from the\nDepartment of Meteorology of the University of Uppsala.\n14.4\nREFERENCES\nAlexandersson, H., and H. Bergstrom (1979): Evaluation of double theodolite pibal track-\ning data. Report No. 55, Dept. of Meteorol., Univ. of Uppsala, Uppsala, Sweden.\nBeran, D. W., and Clifford, S. F. (1972): Acoustic Doppler measurements of the total wind\nvector. Preprints AMS 2nd Symp. on Meteorol. Obs. and Instrum., San Diego, Calif.,\n27-30 March 1972. American Meteorological Society, Boston, Mass., pp. 412-417.\nHolmgren, B. C. Jacobsson, and H. Ottersten (1976): Sondering av atmosfärens gränsskikt\nmed vertikalsodar. FOA rapport C 30077-E1, National Defence Research Institute,\nStockholm, Sweden.\nKaimal, J. C. and D. A. Haugen (1977): An acoustic Doppler sounder for measuring wind\nprofiles in the lower boundary layer. J. Appl. Meteorol. 16:1298-1305.\nOttersten, H. (1975a): Fjärranalys av atmosfärens gränsskikt med sodar och radar. Styrel-\nsen for Teknisk Utveckling. Slutrapport STU 71-727/U 957b, April 1975.\nOttersten, H. (1975b): Swedish sodar investigations and results. Paper presented at the\nURSI XVIIIth General Assembly, Lima, Peru, August 1975, International Union of Radio\nScience, Brussels, Belgium.\nOttersten, H., and F. Eklund (1973): Remote sensing av troposfären. Styrelsen for Teknisk\nUtveckling. Lägesrapport STU 71-727/U 597.\nOttersten, H., M. Hurtig, G. Stilke, B. Brummer, and G. Peters (1974): Shipborne sodar\nmeasurements during JONSWAP II. J. Geophys. Res. 79:5573-5584.\nSalomonsson, S., and J. Ivarsson (1978) Sodar measurements of the boundary layer during\nthe field project \"Stenungsund-77.\" Report No. 50, Dept. of Meteorol., Univ. of\nUppsala, Uppsala, Sweden.\nSmedman-Högstrom, A.-S., and T. Faxén (1980): To be published in report series. Dept. of\nMeteorol., Univ. of Uppsala, Uppsala, Sweden.\nThomson, D. W., and J. P. Scheib (1978): Improved display techniques for sodar measure-\nments. Bull. Am. Meteorol. Soc. 59:147-152.\n86","15. THE XONDAR\nRobert L. Peace, Jr.\nXonics, Inc.\nVan Nuys, California, U.S.A.\n15.1\nINTRODUCTION\nThe XONDAR (Xonics Doppler acoustic radar) is an operational, commercially avail-\nable system. It is designed for a broad range of applications, from mean wind measurements\nto turbulence and diffusion studies. It can also be used in environments ranging from\nbenign to hostile. The XONDAR can vary several key parameters, such as pulse length, pulse\nrepetition frequency, summation time, and observing altitudes, in the field with a simple\ncomputer command. It can also suppress the effects of ambient noise (Balser et al., 1976a).\nOptional equipment includes a sounder printer (to display the time-height distribution of\nrelative stability), hardware to melt ice and snow, and telephone or radio modems.\nTHE BASIC XONDAR ACOUSTIC ANEMOMETER\n15.2\nA basic XONDAR wind-profile measuring system consists of five subsystems: the\nsound-producing and -sensing hardware, the computer, the printer, the program input and\nstorage device, and the command keyboard. Two models of the XONDAR are offered, the Model\n300 and the Model 600. These differ primarily in hardware attributes that give the first\nsystem finer vertical, temporal, and velocity resolution, and the second system a greater\naltitude range. The characteristics and attributes of both models are given in Table 15.1,\nalthough only the longer range Model 600 participated in the intercomparison.\nTable 15.1. XONDAR wind sensor technical specifications\nModel 300\nModel 600\nCharacteristic\n3 ft (0.9 m)\n4 ft (1.2 m)\nAntenna diameter (inside)\nPeak power to transducer (electrical)\n250 W\n250 W\nPeak output power (acoustic)\n40 W\n80 W\n4000 Hz\n2000 Hz\nTransmitted frequency\n160/80 m S\nPulse duration (computer-controlled)\n80/40 m S\n25/12 m\n50/25 m\nAltitude resolution\n0.2/0.4 m/s\n0.2/0.4 m/s\nVelocity accuracy (one component)\n+25 m/s\nMaximum velocity (one component)\n+25 m/s\n5 S\nPulse repetition interval (normal)\n2.5 S\n200 m\n500 m\nNominal maximum altitude for velocity\n400 m\n800 m\nMaximum altitude for sounder\n10\n10\nNumber of altitudes sampled\n2 min\n2 min\nAveraging time (typical)\n115 V +10% @ 30 A, 50-60 Hz\nPower requirements\n87","PROCESSOR SITE\nANTENNA SITES\nCrystal\nOscillator\nTiming Signals\nPulse\nLine\nPower\nTransmit/\nFrom Computer\nGate\nDriver\nAmplifier\nT/R\nReceive\nSW.\nAntenna\nPreamplifier\n#3\nAnalog/Digital\nMultiplexer\nSignal\nPreamplifier\nReceiver\nConverter\nConditioner\n#1\nAntenna 1\nOutput Signal\nPreamplifier\nReceiver\nTo Computer\n#2\nAntenna 2\nFigure 15.1. . . Block diagram of XONDAR sensor subsystem.\nRECEIVER 2\nFigure 15.2. (Above) The three XONDAR\nantenna housings. (Right) The stand-\nard antenna configuration of a Xonics\nthree-component air-motion measuring\nTRANSMITTER/RECEIVER 3\nsystem.\nRECEIVER 1\n15.2.1\nThe Sensor Subsystem\nThe sensor subsystem for both models of XONDAR is composed of one transceiving\nand two receiving antennas and their supporting electronics (Fig. 15.1). Each of the three\nantenna assemblies consists of an aluminum parabolic reflector mounted in the bottom of a\nfoam rubber and lead-lined acoustic shield (Fig. 15.2, above). This shield effectively\nprevents sound from escaping from the transceiver housing or entering any of the housings\n88","Parameter Inputs\nOutput\nTiming (Including\nPulse Signal\nDevice\nReal-Time Clock)\nTo Transmitter\nSampling Signals\nTo Receivers\nDecision\nBuffer\nDigitized\nFFT\nMemory\nLogic\nStorage\nReceived Signals\nFigure 15.3. Block diagram of basic computer functions.\nexcept in the desired direction. At the focal point of the transceiving antenna is an\nacoustic transducer that both emits high-power pulses of sound in a narrow circular beam\nand detects sound returning from the atmosphere.\nThe two outlying receiver antennas are equipped with transducers and feedhorns\nthat detect sound from a range of angles that is narrow in the horizontal but fan-shaped in\nthe vertical and centered on the transmitter beam boresight.\nIn operation, the three XONDAR antennas are nominally located in the right-\ntriangle configuration diagrammed in Fig. 15.2 (right) with an antenna separation equal to,\nor somewhat less than, the maximum altitude to be observed. To avoid loss of sensitivity\nof the horizontal components of air motion, the elevation of the receiving antennas should\nnot exceed 50° to 55°. For the nominal 500-m maximum altitude of the Model 600, antenna\nspacing should be 350 to 400 m. Although the antenna specifications and the configuration\nshown in Fig. 15.2 (right) are optimum, the computer program that performs data reduction\nis sufficiently versatile to allow considerable variation in antenna spacing, orientation,\nand relative height where site constraints dictate.\nThe electrical power requirements of the XONDAR systems are 100-120 V, 50-60\ncycles at 30 A, supplied only at the computer location. The low-voltage power requirements\nof the receiving antennas are provided through the interconnecting cables supplied with the\nsystem. These cables also carry all intelligence to the computer and commands to the\nantennas.\nThe Computer Subsystem\n15.2.2\nThe heart and brain of the XONDAR system are a minicomputer with 32,000 words of\nmemory, a real-time calendar clock, a precision lapsed-time clock, and a nonvolatile memory\nsufficient to read in and restart the program after a power failure. Figure 15.3 is a\ndiagram of the basic functions performed by the computer.\nThe system has considerable flexibility in its configuration, operational mode,\nand data format. The standard selectable system configuration elements are relative antenna\nheight, spacing, and orientation. Selectable operational modes are pulse duration (which\ndetermines velocity and height resolution), pulse repetition frequency (which determines\nmaximum unambiguous observable height as well as the number of samples per summation\nperiod), integration interval (which must balance the frequency of observations against the\nstatistical significance of the data), duration of observation versus no observation (if\nintermittent operation is desirable), and height levels to be sampled (up to 10).\nThe\ndata\n89","output for the basic system can be in either the vector component form (V Vy, V, Ox, Oy'\nOZ), with or without the standard deviation of the velocity component (ox, X Oy's 'z), or the\nmore common polar coordinate form (Az, Sp, 'a' 's, OE) with or without the standard\ndeviations. Additional types of output are available, but they were not used for this\nintercomparison.\n15.2.3\nThe Program-Storage Subsystem\nThe computer program to control the XONDAR's operations, including the default\nvalues of the system configuration, operational mode, and output data format, is provided\non a floppy disk. This disk is read into the computer each time the system is activated\nafter a period of disuse, or when changes in the program or default parameters are desired.\nOnce read in, the program automatically begins operation of the XONDAR. If power is inter-\nrupted during operation, the disk drive automatically rereads the program and default\nparameters into the computer and begins operation whenever power resumes. The real-time\ncalendar clock continues to operate for long periods on its own storage battery. Thus, the\nsystem resumes operation without loss of date or time reference.\nThe residence of both the controlling program and a default value of all opera-\ntional parameters on a floppy disk makes it possible for Xonics to rapidly and economically\nprovide a user with different default values whenever the basic XONDAR use changes. If a\nvariety of operational modes or system configurations is anticipated, Xonics can provide a\ndiskette for each. These are easily inserted into the reader. Thereafter the system will\noperate in accordance with the new instructions until a different diskette is inserted or\nparameters are changed through the keyboard. Should it be desirable to add optional hard-\nware or data-analysis capabilities, the computer program necessary to accomplish the changes\nis also provided by Xonics on a system-compatible floppy disk.\n15.2.4\nThe Printer\nThe system printer is a stand-alone 40-column printer connected to the computer\nthrough a simple cable. This arrangement makes it possible to locate the printer wherever\nmost convenient within several feet of the computer. The unit prints data, heading informa-\ntion, and command prompts and echoes keyboard entries on a 3-in-wide roll of ordinary\npaper. A take-up reel rewinds the paper a few inches beyond the print roller. Sufficient\npaper is exposed to allow examination of two complete 10-level sets of air-motion data\nwithout removing the take-up reel from the printer.\n15.2.5\nThe Keyboard\nAll operational communication with the XONDAR system is accomplished through a\nstandard computer-type keyboard mounted in the computer cabinet. Temporary changes in one\nor more of the operating commands or parameters are easily entered through the keyboard.\nThe new command or parameter overrides the corresponding value in the computer. The new\nvalue is then used until it is changed through the keyboard or overridden by the contents\nof the diskette subsequent to a power interruption or an operator command to read the\ndiskette.\n15.3\nPREVIOUS TESTS OF THE XONDAR\nThis intercomparison of acoustic Doppler radar systems is not the first for\nXonics systems. The earliest prototype XONDAR (a three-antenna, bistatic, two-component\nsystem) was compared with cup anemometers and wind vanes mounted on a 150-m tower at White\nSands Missile Range in 1973 (Balser et al., 1976b). In October 1974, a four-antenna, fully\nbistatic system (made for the Air Force Cambridge Research Laboratory) was compared with\nanemometers on a 500-m tower at the Atomic Energy Commission test site in Nevada (Kaimal\nand Haugen, 1975).\n90","16\n14\n12\n10\nV\nRAD\n8\n(m/sec)\nh= 122m\n6\n4\n2\n10\n12\n14\n16\n-6\n-4\n2\n4\n6\n8\nV\n.-2\nANEM\n(m/sec)\n-4\n-6\n16\n14\n12\n10\nV\nRAD\n8\nh=148m\n(m/sec)\n6\n4\n.2\nFigure 15.4. Overall comparison be-\n4\n6\n8\n10\n12\n14\n16\n-6\n-4\ntween XONDAR-observed wind speeds\nV\n2\n(Vrad) and those reported by an\nANEM\n(m/sec)\nanemometer (Vanem) mounted at the\n-4\n122-m level (upper) and 148-m level\n(lower) of a tower near Boulder,\n-6\nColorado, in 1975.\nIn 1975, a prototype, two-component (wind only) XONDAR was compared against\ninstruments on NOAA's 150-m tower at Boulder, Colorado. Figure 15.4 shows the results of\ncomparisons made by NOAA between the XONDAR and conventional anemometers located at two\nlevels on the tower. Each point in Fig. 15.4 represents a 10-min average speed from both\nthe XONDAR and the corresponding anemometer.\nModel 300 and Model 600 XONDARs have recently undergone a series of comparisons\nagainst tower-mounted anemometers in Japan. Preliminary comparisons were made between a\n4-kHz Model 300 system and anemometers mounted on a 213-m tower in Tsukuba, Japan, in\nDecember 1977. Figures 15.5 and 15.6 show the comparison results.\n91","16\n14\n12\n10\n8\n6\n4\n2\n0\nTime of Day\n1600\n1700\n1800\n1900\n2000\n2100\nN 360\nX\n300\nW\n240\nX\nAnemometer\nXONDAR\nS 180\n120\nE -\n60\nN 0\nFigure 15.5. Comparison of wind speed and wind direction measure-\nments from a Model 300 XONDAR and an anemometer mounted at the\n100-m level of the 213-m high Meteorological Research Institute\n(MRI) tower, Tsukuba, Japan, in December 1977.\n92","16\na\n14\n12\n10\n8\n6\n4\n2\n0\nTime of Day\n1600\n1700\n1800\n1900\n2000\n2100\nN 360\n300\nW\n240\nX\nAnemometer\nS 180\nXONDAR\n120\nE -\n60\nN - 0\n14\nFigure 15.6. Comparison of wind speed and wind direction measure-\nments from between a Model 300 XONDAR and an anemometer mounted\nat the 150-m level of the MRI tower in December 1977.\n93","0 N\n45 NE\n40 E\n135 SE\n180 s\n225 SW\n270 w\n315 NW\n360 N\n18\n19\n20\n21\n22\n23\n0\n14\n0\nN\nWinning\n45 NE\n90 E\n135 SE\nXONDAR (H=75 m L AH )\n180 s\n(H-75m)\n225 SW\n270 w\n3/5 NW\n360 N\nis\n16\n18\n19\n20\n21\n22\n23\nis\nI/C\nm/s\n14\n12\n10\n8\n6\n4\n2\n0\n14\n15\n16\n17\n18\n19\n20\n21\n22\n23\nis\n9/4\n9/5\nn/s\n14\nXondar (H=75mtsH)\n12\nJ-027-> (H=75m)\n(HEA Hile\n10\nto\n8\n6\n4\n2\n0\nis\n16\n17\n18\n19\n20\n21\n22\n23\n0\n9/5\n9/6\nFigure 15 7. A 2-day wind direction comparison (upper) and wind speed com-\nparison (lower) between a Model 600 XONDAR and an aerovane mounted on top\nof a 75-m tower in Japan in September 1978.\n94","In September 1978, a 2-kHz Model 600 underwent a series of tests including compar-\nisons against an aerovane mounted on top of a 75-m tower. Figure 15.7 shows comparisons of\nthe direction and speed data acquired during these tests (Nishinomiya and Akai, 1979).\nThe disparity between XONDAR and anemometer wind measurements is symptomatic of\none of the principal weaknesses of this kind of comparison. By their very nature, tower-\nmounted anemometers of any type measure only the temporal distribution of air-motion condi-\ntions at a fixed point in space. In contrast, Doppler acoustic radars or sounders inter-\nmittently measure the spectrum of velocities in a rather large volume of air within the\ndimensions of the pulse length and beam width of the system. These two types of measure-\nments will agree only to the extent that Taylor's hypothesis-that time variations at a\npoint are due only to displacement of a steady-state field-is valid and that the turbu-\nlence is vertically and horizontally isotropic on a scale commensurate with the acoustic\nDoppler's pulse volume. Since these conditions are rarely completely fulfilled in the\nlower atmosphere, acoustic Doppler and tower-mounted sensor statistics can be expected to\ndiffer, even if both have measured accurately.\nXONDAR APPLICATIONS AND EXAMPLES OF DATA\n15.4\nOnly a few accounts of the applications of XONDAR systems have been published\n(Balser, 1976; Balser et al. 1974, 1976a and b; Noonkester, 1978). These articles refer\nonly to their use for general winds-aloft measurement, wind and wind shear measurements at\nthe end of airport runways, and measurements related to ocean-based convective activity.\nThey have also been used in conjunction with wind-energy exploration, transport and diffu-\nsion, and environmental impact studies.\nSamples of data from one of these applications, part of a Department of Energy\nprogram conducted by Battelle Pacific Northwest, show vertical velocity characteristics of\ninterest to both meteorologists and Doppler acoustic radar designers. These measurements\nwere made near Pittsburg, California (close to the mouth of the Sacramento River) in 1978.\nFigure 15.8 (left) shows the sequential change in vertical velocity from the\nhighest level downward. The shift has just begun during the 2 min ending at 2308, with all\nbut the 400-m level showing upward velocities of 2 to 2.4 m/s. In 2 min the upper two\nlevels have reversed direction of vertical velocity, and the upward velocity has halved at\nthe 300-m level. By 2312 all levels show downward velocity with the greatest downward\nvelocity at the higher levels. The data also show a similar downward progression of wind\ndirection shifts.\nIn contrast, Fig. 15.8 (center) shows vertical velocity reversal at all levels in\nthe 2-min data interval between 1812 and 1814. The horizontal speed shows little change\nwith time, but the 150-m level direction changes 12° in the same 2-min interval that the\nvertical velocity reverses and 5° more in the next 2 min. Direction changes at higher\nlevels follow.\nFigure 15.8 (right) is a 12-min sample of persistent vertical velocity averaging\nmore than 1 m/s at most levels. The significance of such persistence to wind-measuring\nsystems that do not measure vertical velocity was pointed out by Kaimal and Wescott (1976)\nIf bistatic antennas had been located so that the elevation angle to the higher altitudes\nwas about 60° and vertical velocity was not measured, the error in wind measurement would\nhave been 3 to 4 m/s, which is 25% to 30% of the measured values. Furthermore, these\npersistent vertical velocities occurred in the absence of orographic effects, frontal\nactivity, or precipitation, all of which can cause significant vertical velocities (or the\napparent acoustic indication of them) to persist for extended periods. Examination of\nsamples of XONDAR records indicates that persistent vertical velocities are sufficiently\ncommon to cast doubt on any wind data acquired by a Doppler acoustic radar without the\nbenefit of vertical velocity information.\n95","of\ncharacter\nM/SEC\n+.3\n+.2\n-.1\n+.8\n+.8\n+.7\nM/SEC\n+.5\n+1.0\n+1.3\n+1.3\n+1.1\n+1.1\nM/SEC\n+.8\n+.9\n+1.3\n+1.1\n+1.3\n+1.3\nM/SEC\n+.9\n+1.3\n+1.0\n+1.0\n+1.5\n+1.5\nM/SEC\n+.5\n+1.0\n+1.3\n+1.5\n+1.3\n+1.1\nM/SEC\n+.6\n+.5\n+.6\n+.8\n+1.0\n+1.0\nall\nVZ\nVE\nVZ\nVE\nVZ\nVZ\nat\nDEGREES\nDEGREES\nDEGREES\nANGL E\n230.5\nDEGREES\n228.3\n234.3\n230.9\n236.5\n243.5\nANGLE\nDEGREES\n224.9\n232.7\n236.5\n243.0\n233.1\n242.7\nANGLE\n235.5\nDEGREES\n234.1\n231.4\n232.5\n239.3\n247.7\nANGLE\n226.9\n226.6\n231.5\n234.5\n243.3\n245.8\nANGLE\n232.3\n233.6\nthe vertical velocity reversal with height and time. (Center) Note rapid reversal of vertical velocity\n234.0\n235.5\n243.1\n247.0\nANGLE\n229.5\n231.2\n235.9\n240.0\n247.2\n248.0\nthe\nNote\nlevels. (Right) Note consistent upward vertical velocity near 1 m/s at all but the lowest level.\nTIME = 07:11:01\nSPEED\nM/SEC\n+7.5\n+9.4\n+11.3\n+8.1\n+9.3\n+11.2\nTIME = 07:13:01\nSPEED\nM/SEC\n+8.0\n+8.9\n+8.8\n+9.4\n+12.0\n+10.6\n07:15:01\nSPEED\nM/SEC\n+7.4\n+9.5\n+10.3\n+12.3\n+11.9\n+12.4\nTIME = 07:17:01\nSPEED\nM/SEC\n+7.6\n+7.7\n+9.1\n+10.7\n+10.8\n+12.2\nSPEED\nM/SEC\n+7.5\n+8.3\n+10.2\n07:19:01\n+11.0\n+11.0\n+12.0\nTIME = 07:21:01\nSPEED\nM/SEC\n+11.6\nDATE =06/24/78\n+7.1\n+10.1\n+10.7\n+11.7\n+13.0\nDATE =06/24/78\nDATE =06/24/78\nDATE =06/24/78\nDATE =06/24/78\nDATE =06/24/78\n(Left)\nMETERS\nMETERS\nMETERS\nMETERS\nMETERS\nTIME =\nMETERS\nALT\n150\n200\n250\n300\n350\n400\nALT\n150\n200\n250\n300\n350\n400\nTIME =\nALT\n150\n200\n250\n300\n350\n400\nALT\n150\n200\n250\n300\n350\n400\nALT\n150\n200\n250\n300\n350\n400\nALT\n150\n200\n250\n300\n350\n400\nCalifornia.\nPittsburg,\nM/SEC\n+.1\n+.2\n+.3\n+.7\n+.9\n+1.2\nM/SEC\n+.7\n+1.0\n+.9\n+1.0\n+1.2\n+1.1\nM/SEC\n-.4\n-.2\n-.2\n-.2\n-.2\n-.3\nM/SEC\n-.0\n-.2\n-.2\n-.2\n-.2\n-.4\nM/SEC\n-.3\n-.4\n-.2\n-.3\n-.3\n-.7\nM/SEC\n+.3\n+.0\n+.2\n+.0\n-.0\n+.0\nVZ\nVZ\nVE\nVE\nVZ\nVZ\nDEGREES\nDEGREES\nDEGREES\nDEGREES\nANGL E\n264.5\nDEGREES\n258.9\n258.9\n258.4\n257.6\n258.0\nANGLE\n260.5\n257.0\n256.6\nDEGREES\n256.9\n257.6\n264.5\n248.1\n253.4\n254.3\nANGL E\n251.1\n254.4\n255.0\n243.9\n249.3\n249.6\n252.3\nANGL\n247.1\n249.9\nANGLE\n251.6\n250.2\n253.0\n253.1\n257.0\n260.4\nANGLE\n249.2\n253.0\n259.0\n256.9\n263.4\n266.9\nnear\nacquired\nSPEED\nM/SEC\n+6.4\n+6.4\n+6.5\nTIME = 18:10:01\n+6.8\n+6.4\n+5.5\nM/SEC\n18:12:01\nSPEED\n+6.3\n+6.5\n+7.0\n+6.5\n+6.6\n+6.5\n18:14:01\nSPEED\nM/SEC\n+6.1\n+6.1\n+6.7\n+6.8\n+6.9\n+7.0\n18:16:01\nSPEED\nM/SEC\n+6.3\n+6.9\n+6.8\n+6.3\n+5.7\n+6.7\n18:18:01\nSPEED\nM/SEC\n+6.8\n+6.6\n+7.1\n+6.8\n+6.8\n+7.1\nM/SEC\n18:20:01\nSPEED\n+6.6\n+6.5\n+7.0\n+6.7\n+6.8\n+6.7\nDATE 06/26/78\nDATE =06/26/78\nDATE =06/26/78\nDATE =06/26/78\nDATE =06/26/78\nDATE =06/26/78\nMETERS\nMETERS\nMETERS\nMETERS\nMETERS\nTIME =\nTIME =\nMETERS\ndata\nALT\n150\nTIME =\n200\n250\n300\n350\n400\nALT\n150\nTIME =\n200\n250\n300\n350\n400\nALT\n150\n200\n250\nTIME =\n300\n350\n400\nALT\n150\n200\n250\n300\n350\n400\nALT\n150\n200\n250\n300\n350\n400\nALT\n150\n200\n250\n300\n350\n400\nXONDAR\nof\nM/SEC\nsamples\n+2.0\n+2.4\n+2.4\n+2.1\n+2.1\n+1.1\nM/SEC\n+1.9\n+1.8\n+1.0\n+2.1\n-.7\n-.1\nM/SEC\n-.8\n-.2\n-.8\n-1.2\n-1.6\n-1.6\nM/SEC\n-1.0\n-1.4\n-.3\n-1.5\n-1.0\n-1.0\nM/SEC\n-.2\n-.4\n-.8\n-.6\n-1.5\n-1.4\nM/SEC\n-.2\n-.2\n-.4\n-.8\n-1.5\n-2.0\nVZ\nVZ\nVE\nVE\nVZ\nVZ\nDEGREES\nDEGREES\nDEGREES\nANGLE\nDEGREES\n242.3\n243.2\n243.4\nDEGREES\n243.8\n259.6\n258.1\nANGLE\n235.5\n245.5\n244.3\n251.8\n266.4\nDEGREES\nTwelve-minute\n253.1\n243.5\n242.6\n248.4\n257.7\n250.9\n272.4\nANGLE\nANGLI\n240.1\n241.8\n254.3\n251.5\n255.8\n257.7\nANGLE\n242.7\n242.6\n245.8\n254.6\n256.8\n288.9\n245.5\nANGLE\n242.4\n247.3\n253.8\n855.7\n258.1\nTIME = 23:08:00\nSPEED\nM/SEC\n+9.4\n+9.9\n+8.8\n+8.8\n+10.2\n+11.5\nTIME = 23:10:00\nSPEED\nM/SEC\n+9.9\n+11.6\n+8.5\n+12.4\n+8.1\n+10.9\n23:12:00\nSPEED\nM/SEC\n+10.4\n+10.6\n+10.8\n+12.0\n+13.8\n+12.1\nTIME = 23:14:00\nSPEED\nM/SEC\n+11.2\n+11.5\n+8.9\n+12.9\n+11.9\n+12.7\nTIME = 23:16:00\nSPEED\nM/SEC\n+10.2\n+10.8\n+11.3\n+11.0\n+11.9\n+10.9\nTIME = 23:18:00\nSPEED\nM/SEC\n+10.4\n+9.7\n+10.7\n+11.2\n+13.4\n+13.3\nDATE =06/24/78\nDATE =06/24/78\nDATE =06/24/78\nDATE =06/24/78\nDATE =06/24/78\nDATE =06/24/78\nMETERS\nMETERS\nMETERS\nMETERS\nMETERS\nTIME =\nMETERS\nALT\n150\n200\n250\n300\n350\n400\nALT\n150\n200\n250\n300\n350\n400\nALT\n150\n200\n250\n300\n350\n400\nALT\n150\n200\n250\n300\n350\n400\nALT\n150\n200\n250\n300\n350\n400\nALT\n150\n200\n15.\n250\n300\n350\n400\nFigure","REFERENCES\n15.5\nBalser, M. (1976) : Measuring wind shear. In Airports International, IPC Business Press,\nSurrey, England.\nBalser, M. , C. A. McNary, and A. E. Nagy (1974): Acoustic backscatter radar system for\ntracking aircraft trailing vortices. J. Aircraft 11:556-562.\nBalser, M. , C. A. McNary, and D. Anderson (1976a): A remote acoustic wind sensor for\nairport approaches. J. Appl. Meteorol. 15:665-668.\nBalser, M. , C. A. McNary, A. E. Nagy, R. Loveland, and D. Dickson (1976b) : Remote wind\nsensing by acoustic radar. J. Appl. Meteorol. 15:50-58.\nKaimal, J. C., , and D. A. Haugen (1975): Evaluation of an acoustic Doppler radar for measur-\ning winds in the lower atmosphere. Proc. 16th Radar Meteorol. Conf., 22-24 April\n1975, Houston, Tex., American Meteorological Society, Boston, Mass., , p. 312.\nKaimal, J. C. , and J. W. Wescott (1976) : An acoustic Doppler sounder for measuring wind\nprofiles in the lower boundary layer. Proc. 17th Radar Meteorol. Conf., 26-29 October\n1976, Seattle, Wash., American Meteorological Society, Boston, Mass., pp. 290-296.\nNishinomiya, S. , and Y. Akai (1979): Wind profile measurements with a Doppler-acoustic\nremote sensor in the lower atmosphere. Central Research Institute for Electric Power\nIndustry, Iwato 1, 229, Komae City, Tokyo, Japan (in Japanese), 28 pp.\nNoonkester, V. R. (1978): Multi-sensor measurements of ocean based convective activity.\nProc. 18th Radar Meteorol. Conf., 28-30 March 1978, Atlanta, Ga., American Meteorolog-\nical Society, Boston, Mass. , pp. 55-64.\n97","16. GMD-1 RADIO WIND SOUNDING SYSTEM\nRobert B. McBeth\nNational Center for Atmospheric Research\nBoulder, Colorado, U.S.A.\n16.1\nPURPOSE AND USE\nThe GMD-1 rawin set is a transportable radio direction finder that automatically\ntracks a balloon-borne radiosonde transmitter. A radio signal containing meteorological\ninformation in the form of amplitude or frequency modulation is received, amplified, and\ndetected by this equipment. The detected radiosonde signal is passed to separate equipment\nin the system where it is recorded. By reference to calibration data, these recorded data\nare converted to values of temperature, humidity, and pressure. Recordings of time versus\nprogressive changes of the elevation and azimuth positions of the ascending balloon, as\ndetermined by tracking of the signal from the radiosonde, are converted to wind speed and\ndirection.\n16.2\nSYSTEM COMPONENTS\n16.2.1\nRadiosonde VIZ 1680 MHz\nThis equipment consists of a transmitter, a modulator, an antenna, a battery, and\npressure-, temperature-, and humidity-sensing elements. The pressure capsule employed is\ntemperature-compensated and constructed to give approximately logarithmic response over the\noperating range. The temperature element is a rod of ceramic material with a high negative\nresistance coefficient. The humidity sensor is a plastic strip with a gelatinous cellulose\ncoating that contains finely divided carbon particles in suspension. Resistance of the\nsensor increases with relative humidity.\nThe radiosonde in use for the low-level experiment was the VIZ 1680-MHz radio-\nsonde equipped with ACCU-LOK sensors. These sensors are calibrated at the factory, thus\neliminating the need for a baseline check before each observation. The assembled instru-\nment weighs about 800 g and can be carried to an altitude of 30 km by a helium-filled\nballoon. The battery furnishes power to the transmitter and modulator. The transmitter\noperates in the 1660- to 1700-MHz band, and its carrier is amplitude-modulated by an\naudiofrequency pulse, the rate of which is determined by the pressure-, temperature-, and\nhumidity-sensing elements.\nSwitching between temperature, relative humidity, and a calibration signal\n(reference) is achieved by a pressure-operated device called a baroswitch. With the\nascent of the radiosonde the expansion of an aneroid capsule, through connecting mechanical\nlinkage, causes a contacting pen to travel across a printed circuit board array of silver\nconducting strips mounted on insulated material. This is termed the commutator.\nWhen the baroswitch pen rests on an insulated portion of the commutator the value\nof air temperature is transmitted by the radiosonde unit. The silver segments of the\ncircuit board are used to switch the sonde to reports of relative humidity or references.\nThe first four of every five silver segments on the commutator switch the radiosonde to\nreport values of relative humidity whereas the fifth, tenth, fifteenth, etc., silver seg-\nments direct the sonde to a circuit which provides a fixed frequency of about 190 Hz. When\nthis frequency is received at the ground station the meteorological recorder pen moves to\napproximately the 95th ordinate of the recording chart. This provides the radiosonde\noperator with a reference that enables him to adjust the setting of the recorder to\nexactly 95 ordinates and thus remove any subsequent linear errors in the temperature and\n98","humidity values to be received until the next reference. On most U.S. radiosonde devices\nthe 30th, 45th, 60th, etc., contact reports a slightly greater frequency, termed the high\nreference, which is used to facilitate counting the number of contacts received at the\nground station.\nEvery radiosonde unit is delivered with a calibration chart which provides a\nvalue of pressure for each contact of the particular sonde.\n16.2.2\nRawin Set\nThe rawin set automatically tracks by continuous homing on the radiosonde signal.\nThe equipment indicates and records the azimuth and elevation angles of the radiosonde.\nThese angles are plotted with the height (computed from the pressure and temperature data)\nto determine wind direction and speed.\nRecording Equipment\n16.2.3\nRadiosonde meteorological data (temperature, humidity, reference data) are\nrecorded on a time-frequency strip chart recorder. Elevation, azimuth angles, and elapsed\ntime after balloon release are printed on paper tape.\nTECHNICAL CHARACTERISTICS\n16.3\nPower input to the system is 05-129 - V a. C , 50-65 Hz, 1,000 W. The frequency\nrange is 1660-1700 MHz, and either an AM or FM signal can be used.\nThe RF system features conical scanning with a single dipole antenna and\na\nparabolic reflector. The receiving system uses a superheterodyne receiver and an IF\nfrequency of 30 MHz; its tracking accuracy is 0.05° maximum error between 10° and 60°\nelevation.\nThe antenna positioning system features automatic tracking, with the option of\nmanual control locally.\nDATA PROCESSING\n16.4\nAt most operational GMD radiosonde stations data are manually processed. Temper-\nature and humidity strip chart records and printed elevation and azimuth angles from the\ncontrol recorder are analyzed with the aid of slide rules, graphs, and scales to yield\nprofiles of temperature, humidity, and wind. For the BLIE, with six scheduled soundings\nper day (two of these on the tower carriage), there was not enough time for manual process-\ning. Instead the operator manually transcribed data from the two hard-copy records onto a\nmagnetic tape from which the data were entered by phone line into a Bureau of Reclamation\ncomputer. When conventional radiosonde reduction programs were used, the computer yielded\nprocessed data on a printer at the field site with a normal turnaround time of 1 min.\n99","17. TDFS LOW-LEVEL RADIOSONDE SYSTEM\nC. Fink and E. Schöllmann\nUpper-Air Research Station\nDeutscher Wetterdienst\nMunich, Federal Republic of Germany\nA. Kölbl\nInstrument Division\nDeutscher Wetterdienst\nMunich, Federal Republic of Germany\n17.1\nLOW-LEVEL SONDE TDFS\nThe low-level sonde TDFS is a lightweight weather sonde for measuring tempera-\nture, humidity, and atmospheric pressure in the free atmosphere up to about 600 mb. For\ndry- and wet-bulb temperatures, bead thermistors with negative temperature coefficient\n(NTC) resistance, having diameters of 0.4 mm, are used. The measuring range is from -40°C\nto +40°C. The frequency of a subcarrier oscillator is changed in the range of 300-900 Hz\nby the temperature behavior of the NTC resistance. This subcarrier frequency modulates a\ncrystal-controlled transmitter with a frequency between 402 and 406 MHz. The exact fre-\nquency can be determined subsequently for each sonde by a plug-in crystal. The modulated\nsignal is transmitted by a half-wavelength antenna, which also serves as a means for sus-\npension. Two small 9-V dry batteries are used for the power supply. The pressure-\nmeasuring element is an aneroid capsule of copper beryllium, which is temperature com-\npensated over the entire measuring range. The measuring range of about 1,050 mb to about\n600 mb is subdivided by gold-plated contacts in pressure steps of about 25 mb. The\nfeatures of the sonde are listed in Table 17.1.\nThe case is made of white plastic that insulates well against cold. Its dimen-\nsions are 206 X 170 X 85 mm; the weight including batteries is 300 g. Both temperature\nsensors are housed in a foamed plastic tube that protects the sensors from mechanical\ninfluences and direct solar radiation and provides for an optimal air flow. Three views\nof the sonde are shown in Fig. 17.1.\n17.2\nRECEIVING STATION KS 75\nThe signals of the radiosonde are received by the UHF radiosonde receiver. Here\nthe demodulation takes place; i.e., the measuring signals (frequencies of 300-900 Hz) are\nseparated from the high frequency carrier and are available for further processing at the\nreceiver output.\nThe special data-handling unit allows the low frequency signals of the sondes to\nbe automatically evaluated. For this purpose four coefficients have to be inserted to\ndescribe the corresponding calibration curve. On the basis of the inserted sonde calibra-\ntion curve, a microprocessor calculates the digitally measured low frequency values and\nshows a temperature in degrees Celsius in a digital display, at 1-s intervals.\nDuring sonde reception the dry- and wet-bulb temperatures are received alter-\nnately, interrupted at irregular intervals by pressure signals that are represented on the\nstrip chart recorder as rectangular steps. Figure 17.2 illustrates a portion of a typical\nstrip chart record. Temperature values of -50°C to +50°C can be recorded with a resolution\nof 0.4°C/mm.\nTwo digital outputs (TTL level, BCD 1,2,4,8) available at the back of the\nreceiving station make it possible to connect tape punches (e.g., hp 3,489 A) or computers\n100","Table 17.1. Description of the low-level sonde TDFS\nDescription\nFeature\nHeight\n206 mm\nDimensions\nWidth\n170 mm\nDepth\n85 mm\nWeight with battery\n300 g\nFor dry- and wet-bulb temperature,\nSensors\nmatched bead thermistors, var-\nnished in white; diameter 0.4 mm.\n-40°C to +40°C\nTemperature-measuring range\nAneroid capsule, CuBe\nPressure-measuring element\n1,050 mb to ~600 mb in pressure steps\nPressure-measuring range\nof ~25-mb intervals; every fifth\npressure step is a double step.\nPressure\n+0.5 mb\nResolution\n+0.1°C\nTemperature\nPressure\n+2 mb\nAccuracy of system\n+0.4°C\nTemperature\nPsychrometric\ndifference\n+0.2°C\n402 to 406 MHz crystal-controlled\nTransmitter frequency range\n~25 mW\nTransmitter power\nFrequency modulation\nModulation\n300 to 900 Hz\nSubcarrier frequency\n+6 kHz\nFrequency bandwidth\n+30 ppm\nFrequency stability\nHalf-wavelength comnidirectional\nAntenna\nVertical\nPolarization\n~45 min with alkali-manganese cells,\nDuration of operation\nMallory MN 1604\nfor further processing of the data. The features of the receiving station are summarized\nin Table 17.2. The receiving station and the radiosonde were developed for the Deutscher\nWetterdienst by Instrumentenamt München.\nEVALUATION\n17.3\nReceiving station KS 75 produces an analog record (see Fig. 17.2) containing\natmospheric pressure in the form of pressure steps and the dry- and wet-bulb temperature,\nin the correct physical units. The dry-bulb data are recorded during a period of about\n6 S, and the wet-bulb data during a period of about 3 S. From the calibration table\nattached to each sonde the values of the pressure levels are obtained and the pressure\ntime curve is plotted as shown in Fig. 17.2. Intermediate pressures may be interpolated\n101","C\ne\n925117\nNo\n925117\nb\nFigure 17.1. . . Low-level - radiosonde of\nthe Deutscher Wetterdienst : (above,\nleft and right) cover removed to\nshow (a) aneroid capsule, (b) bat-\nteries, (c) sphere, to create a tur-\nbulent air flow, (d) blackened air-\nduct, (e) dry-bulb - thermistor, (f)\nwet-bulb thermistor, and (g) array\nof pressure contacts; (left) cover\non for balloon launch.\n102","Calibrated\nPressures\nOver\nice\n606 mb\nWet bulb freezing\nOver\nwater\n630\n641\n666\n692\n717\n744\nDry bulb temperature\nWet bulb temperature\n766\n776\n792\nPlotted pressure vs. time\n853\n878\nGround Check: P = 965.1 mb\n905\n913\nT = 18.7°C\nTw = 12.5°C\n942\nStart\n600\n650\n700\n750\n800\n850\n900\n950\n1000\n-30\n-20\n-10\n0\n10\n20\n30\n40\n50\nPressure (mb)\nTemperature (°C)\nFigure 17.2. Analog record of a sounding showing the pressure vs. time curve plotted from\nthe pressure calibration of the sonde and the occurrences of pressure readings. Note\nthe warming to 0°C of the wet bulb at the instant of freezing.\nfrom this curve. Then the significant levels of the dry- and wet-bulb temperature are\nselected. Pressure and dry- and wet-bulb temperatures for each significant level and for\nany mandatory pressure levels are inserted in a small programmable calculator to yield\nrelative humidity, dew point, and height. The data for mandatory height levels are deter-\nmined by interpolation. If a calculator is not used, the relative humidity has to be\ndetermined from psychrometric tables. The computation of the height is then made by using\nthe Stüve diagram.\n103","Table 17.2. Description of receiving station KS 75\nFeature\nDescription\nDimensions\nHeight\n440 mm\nWidth\n520 mm\nDepth\n400 mm without paper cas-\nsettes and dust cover;\n490 mm with cassettes and\ncover.\nWeight\n40 kg\nPower input\n220 V + 10%, 50 Hz + 20%, 100 VA\nInput of calibration curve\n4 coefficients\nTemperatures\nDigital indication\nAnalog recording\nAlternating between dry- and wet-\nbulb temperatures, interrupted by\npressure steps; temperature range\n-50°C to +50°C.\n17.4\nACCURACY\nEach sonde is calibrated by the manufacturer. The conversion of frequency into\ntemperature is made by means of a polynomial of the third degree. Since only the coeffi-\ncients of one calibration curve can be inserted into the receiving station KS 75, the therm-\nistor for dry- and wet-bulb temperatures have to be matched. A deviation of +0.1°C is\nacceptable. Because of digitalizing, the resolution of the station amounts to 0.1°C.\nWhen all sources of error are combined, the system accuracies are +0.4°C for temperature\nand +0.2°C for psychrometric difference. The lag-coefficient of the bead thermistors is\nabout 2 s; it is larger with ice accretion. The change of the water from liquid to solid\non the wet-bulb thermometer takes about 30 to 60 s, depending on the degree of supercooling\nand the moisture content of the air.\nWhen a pressure step is reached during the ascent, a fixed resistor is switched\nin instead of the temperature sensor. The resulting step change in frequency provides an\nindication of the pressure contact on the strip chart. When the points are connected it\nyields the pressure versus time curve in Fig. 17.2. The leading edge is chosen for the\ncalibration value. The calibration accuracy is +0.5 mb. The occurrence of the event is\nreported with a maximum delay of 0.5 S. The accuracy of the entire system is +2 mb.\n104","18. CORA RADIOSONDE SYSTEM USING FREE-FLYING BALLOONS\nIlkka Ikonen\nVaisala Oy\nHelsinki 42, Finland\nCORA is an automatic upper-air system commercially available from Vaisala. The\nsystem is equipped with automatic computation and analog output for monitoring purposes.\nManual evaluation is possible by using the analog output of radiosonde frequencies. The\nprogram for upper-air sounding stations, which make soundings for meteorological networks,\nis called CORA 6. In the BLIE a special computer program called CORA 8 EXP was used. The\nradiosonde used by the system is the Vaisala RS 21-12 CN, shown in Fig. 18.1.\nRADIOSONDE RS 21-12 CN\n18.1\nGeneral Characteristics\n18.1.1\nThe general characteristics of radiosonde 21-12 CN are as follows:\nOutput frequency: 46.1 to 50.8 kHz.\nCarrier frequency: 403 MHz (adjustable +3 MHz).\nSensors: Low-altitude pressure P, aneroid barometer.\nHigh-altitude pressure PP (above 150 mb), aneroid barometer.\nHumidity U, Humicap thin film capacitor.\nTemperature T, NiFe-alloy bimetal.\nTwo reference capacitors K1 and K2.\nVLF receiver for the Omega system (13.6 kHz).\nRS 21\nFigure 18.1 Vaisala radiosonde\nRS 21-12 CN before launch\nduring BLIE.\n105","The pressure and temperature sensors are linked mechanically to variable capaci-\ntors. Each of the six elements is connected in sequence to the modulating circuit by a\nswitch attached to a rotating reel. The sonde is tied to the balloon by a line running\nfrom the reel. During ascent the weight of the sonde pulls line from the reel, causing it\nto rotate. During one cycle each element transmits for about 1.6 S. Winds are derived\nfrom the VLF reception of Omega signals.\n18.1.2\nCalibration\nEach radiosonde is individually calibrated in the factory. Numeric calibration\ncoefficients for P, PP, and T are available for automatic computation. U calibration is\ncarried out during baselining.\n18.2\nGROUND EQUIPMENT\nHardware consists of the following main parts:\nTeletype 43 ASR.\nNOVA 2 minicomputer with 64-Kbyte memory.\nNOVA cassette (3-drive C-cassette).\n400-MHz receiver.\nOmega receiver.\nRadiosonde signal sampling unit.\nAntennas for 400-MHz and local Omega reception.\nAnalog output devices for monitoring and manual evaluation.\nBaselining equipment.\n18.3\nAUTOMATIC COMPUTATION\n18.3.1\nOutput Format\nThe system offers two possibilities for data output: teletypewriter and\nC-cassette. Output made on the teletype has the following format:\ntttt zzzzz PPPPP +TTT UU DDD FFF,\nwhere\ntttt\nis time for the level in seconds;\nzzzzz\nis height in geopotential meters computed from pressure, temperature,\nand humidity using the hydrostatic equation;\nPPPPP\nis pressure in 0.1 mb;\nTTT\nis temperature in 0.1°C;\nUU\nis relative humidity in %;\nDDD\nis wind direction in degrees;\nand\nFFF\nis wind speed in 0.1 m/s.\nThe system offers a wide variety of post-ascent processing capabilities using\nthe data stored on the magnetic cassettes. Programs can be written and run in BASIC\nlanguage using the CORA equipment.\n106","Automatic Computation of PTU\n18.3.2\nRadiosonde signals from the six elements are received continuously, six fre-\nquencies in sequence per data frame. Each of the six frequencies is passed through its\nown digital filter that rejects impossible values.\nMeteorological values are computed using the following procedure:\n(1) Compute the corrected element value for P, PP, T, and U using the element in\nquestion and both reference capacitors.\n(2) Compute the humidity value using a predefined calibration equation that is\nfixed during baselining.\n(3) Compute pressure and temperature using individual calibration equations of\nsecond degree.\nPressure, humidity, and temperature at a specified time are computed as weighted averages\nof the two nearest observed values. Weighting is in proportion to nearness to the speci-\nfied time.\n18.3.3\nManual Computation of PTU\nManual computation is easily carried out by an operator using the automatic\nradiosonde receiver and evaluation ruler.\n18.3.4\nWind Computation Specification\nWind computation is based on the Omega network. All eight Omega stations are\nalways used. Both local wind and remote wind are determined, and a differential cor-\nrection is made optionally. Wind is reported each 10-s interval, which corresponds to\na\nfull Omega sequence. In derivative computation a sliding second-degree curve across\n4 min is used. A weighting is carried out to get an optimal solution in the sense of\nleast squares fitting. If the quality is under a certain pregiven level, the weight of\nthat particular signal is zero. Although the accuracy of Omega-derived winds depends on\nlocal Omega reception conditions, it is the experience of Vaisala that, in most cases, the\nwind vector is accurate within 1-2 m/s.\n18.4\nINTERCOMPARISON DATA\n(1) Automatic computation listing in the format described in 18.3.1, at 10-s in- -\ntervals.\n(2) Pressure, temperature, and humidity transferred on the Vaisala low-level sound-\ning aerogram.\n(3) Manual readings from automatic radiosonde receiver, transferred on the Vaisala\nlow-level sounding aerogram.\n107","19. THE AIRSONDE SYSTEM\nDavid B. Call\nAtmospheric Instrumentation Research, Inc.\n220 Central Ave.\nBoulder, Colorado, U.S.A.\nAlvin L. Morris\nAmbient Analysis, Inc.\n3300 Arapahoe Ave.\nBoulder, Colorado, U.S.A.\n19.1\nINTRODUCTION\nThe Airsonde TM meteorological sounding system (Fig. 19.1) is a complete, highly\nportable system in which precision sensors and solid-state electronics are combined to\nyield digital data in standard meteorological units in real time. It is designed for use\nwith small (30- and 100-g) balloons and is capable of reaching heights greater than 10 km.\nThe Airsonde sensor package (hereafter called the Airsonde) is contained in an\nexpanded polystyrene package (see Fig. 19.2) in the form of a helicoid propeller. As it\nrises or descends, its spinning aspirates two bead thermistors mounted in radiation shields\nat the tips of the propeller. One is covered by a wick that is wetted by water contained\nin a small reservoir, and the two form a psychrometer. Pressure is sensed by an aneroid\ncapsule whose temperature is measured by a third bead thermistor. No baseline measurements\nare required for most uses of the Airsonde system.\nFigure 19. 1. The Airsonde system with an\ninflated 30-g balloon. The aluminum case\nto the left contains the ground station.\n108","Radiation Shield\nWater Reservoir\nRadiation\nShield\nthree\nThermistor (Dry Bulb)\nThermistor (Wet Bulb)\nAntenna\nFigure 19.3. Airsonde ground station\nFigure 19.2. Schematic diagram of an\nmounted in aluminum suitcase. Modified\nAirsonde.\nHP-97 is shown in foam cutout. Similar\ncutout is for tape recorder beside\nAirsonde in front of case.\nAn electronic multiplexer samples the sensors sequentially once every 6 S. The\nAirsonde mass, complete with battery, is 130 g. The transmitter, a narrow-band, crystal-\ncontrolled, solid-state device, transmits data in analog form, radiating 25 mW of power at\na frequency of 403.5 MHz.\nThe Airsonde ground station (Fig. 19.3) is interchangeable with that of the\nTethersonde, described in Chapter 20. Enclosed in an aluminum case, the ground station\nconsists of a receiver, a small strip chart recorder, a microcomputer, a visual digital\ndisplay, a battery charger, and a power supply. It may be operated on either 110 V a.c.\nor 12 V d.c. For soundings up to 300 mb the ground station may be used with an omnidirec-\ntional, half-wave antenna; for higher-level soundings a higher-gain antenna is used.\nIn the ground station the incoming analog telemetry signal is converted to a\ndigital signal, which is then processed by the microcomputer. Digital data from the\nground station may be printed on a modified Hewlett-Packard Model HP-97 programmable\nprinting calculator, or recorded on either digital or analog tape recorders. Table 19.1\nshows sample printout information from an HP-97 during an Airsonde flight. Figure 19.4\nis a graph of the Airsonde sounding data from a flight.\nOPERATIONAL CHARACTERISTICS\n19.2\nThe Airsonde used in BLIE measured pressure, temperature, and wet-bulb tempera-\nture. Complete profiles of these variables, or of variables such as relative humidity or\npotential temperature that can be derived from the measured variables, are attainable.\n109","Table 19.1. Examples of Airsonde system data printouts from a\nmodified HP-97 printing calculator\nObserved and calculated\nObserved data printout*\ndata printout\nVariables\nPrintout\nVariables\nPrintout\nTime\n20.8\n***\nTime\n9.2139\nT (°C)\n15.4\n***\nP (mb)\n818.6\nTw(°C)\n8.6 ***\nT (°C)\n9.0\nP(mb)\n820.4\nRH (%)\n43.8\nw(g/kg)\n6.0\n(m)\n17.6\ne(K)\n305.6\n***\n* A real-time printout of observed data only. The time, 20.8, is elapsed\ntime in decimal minutes after the ground station was set to receive and pro-\ncess data. Real-time printout is for every second or third frame of data.\n+ A printout of observed and calculated data from post-flight playback of\ntape recorded data. The time is read 9 h, 21 min, and 39 S. On playback\nevery data frame can be printed out if desired.\n§ Note that the variable columns shown here are not part of the HP-97\nprintout.\nThe basic Airsonde ground station is quite versatile because it has both analog\nand digital outputs and because it interfaces with a number of peripheral devices. Commu-\nnication with these devices is through two 25-pin connectors, one of which provides RS-2320\nand 20-mA signal levels to operate a cathode ray terminal, teletypewriter, or modified\nHP-97 printing calculator, whereas the other provides a terminus of 16 bi-directional data\nlines, 8 of which are control lines. The latter connector gives the user a general-purpose\nprogrammable interface and provides control and data signals as well as power for recording\ndata in ASCII FSK on an analog cassette tape recorder.\nThe most commonly used peripherals are a magnetic tape recorder and a modified\nHP-97 calculator. Digital data are tape recorded during flight. In addition the HP-97 may\nbe used to calculate data shown in Table 19.1 (right) for every fifth frame or to print\nevery third frame in real time. After the flight the taped record may be played back\nthrough the ground station to the HP-97 at a selectable slower rate, and the HP-97 may be\nprogrammed to do various calculations with every data frame, printing calculated as well\nas measured variables.\nThe program has certain editing features. For example, while integrating the\nhydrostatic equation to calculate height, the program compares current and previous frames\nof data for apparent discrepancies. If the difference in either temperature or pressure is\nexcessive according to the criteria programmed into the calculator, the program rejects the\ncurrent data for calculations, but prints current time, pressure, and temperature. The\noperator can observe these and override the program decision at will.\nThe Airsonde is normally flown on either a 30- or 100-g balloon. Guidelines for\nballoon inflation are provided by the curves of Fig. 19.5, which relate ascent rate of the\nAirsonde to weigh-off mass. (Weigh-off is the total mass, including inflation device,\nsuspended from the balloon during inflation. Gas is added until the balloon is in neutral\nequilibrium with the weigh-off mass.) Separate curves are given for both helium and hydro-\ngen and for 30- and 100-g balloons. The curves are approximate and are based on data ob-\ntained by dropping the Airsonde from a tower and considerations of balloon drag and buoy-\nancy. An ascent rate of more than 1 m/s is necessary to assure adequate aspiration of the\npsychrometer. In the intercomparison experiment the Airsonde was flown in tandem with\nother types of radiosondes from a single 300- g balloon.\n110","Airsonde Sounding-Marshall, Co., 0921 MST, 29 Apr. 1978\n250\n250\n50\n100\n5 (m/s)\n0\nRH\n300\n300\nX\n400\n400\nV2\nRH\nT\n500\n500\n600\n600\nWet bulb freezing-Rdg 0.1°\n700\n700\n800\n800\nX\n900\n900\n1000\n1000\n10\n-20\n-10\n15\n-45\n-40\n-35\n-30\n-25\n-15\n-5\n0\n5\nTemperature (°C)\nFigure 19.4. Sample Airsonde sounding, every fifth data frame, with addi-\ntional detail between 750-760 mb and 550-560 mb. Note that the wet-bulb\nfreezing temperature provides a convenient temperature check. The HP-97\nprogram used for this sounding calculates vapor pressure over ice for\nall values of T <0°C.\nSENSOR CHARACTERISTICS\n19.3\nTemperature-Humidity\n19.3.1\nThe precision bead thermistors used in the Airsonde are epoxy-coated sensors\nmanufactured to precise tolerances. Interchangeability and accuracy of +0.2°C from +50°\nto -20°C are stated by the manufacturer; typical performance is better.\nThe Airsonde system ground station measures the resistance of each thermistor and\ninterpolates data from a table to derive dry-bulb and wet-bulb temperatures. Error intro-\nduced by the mathematical computation is an insignificant 6.0 X 10 3 °C in the worst case.\nSince the psychrometric technique of measuring humidity is more sensitive to wet- -\nbulb depression than to either dry- or wet-bulb temperature, the circuitry was designed to\nassure an accurate measure of the depression. An electronic multiplexer switches the dry-\nand wet-bulb - thermistors into the measurement circuitry within 1 S of each other during\neach 6-s frame. This is considerably faster than an Assmann psychrometer can be read.\nA\npossible 0.1°C error, traceable to manufacturing tolerances in reference resistors and to\n111","600\nHelium\n500\nHydrogen\n400\n100 g\n300\n200\n30 g\n100\nV Z (ft/min)\nFigure 19.5. Graphic aid for\n(X102)\ncalculating the weigh-off\n1\n2\n3\n4\n5\n6\n7\nmass to be used when inflat-\n0\ning Airsonde balloons.\n0\n1\n2\n3\n4\nV Z (m/s)\nswitch resistance, is common to both dry- and wet-bulb temperatures and is therefore absent\nfrom the wet-bulb depression.\nGood psychrometry requires that the sensors be properly exposed. They must be\nadequately aspirated and protected from the effects of radiation. Fast response is essen-\ntial in a sounding system that moves rapidly through strata in which humidity gradients are\nlarge. The dry-bulb thermistor has a time constant of 10 S in still air and 3 to 5 S with\nthe rotational aspiration that occurs at nominal ascent rates (2 to 4 m/s). The wet-bulb\nresponse time, which has been observed only in a very limited way, is believed to be about\nthree times that of the dry bulb.\nEach thermistor is mounted in its own radiation shield. The shield, a tube of\nmolded expanded polystyrene, has small thermal mass and is a good insulator. Since the\nAirsonde rotates about a vertical axis during flight, direct insolation to the bead can\noccur for only a small fraction of each rotation and is therefore not significant. Diffuse\nradiation is minimized by blackening the inside surfaces of the shields.\nAspiration is achieved by the spinning of the helicoid propeller-shaped Airsonde\nas it ascends or descends. A minimum aspiration rate of 3 m/s is recommended (Bindon,\n1965) The Airsonde is designed to produce an airspeed past the propeller tips equal to\n112","three times its ascent rate. The helicoid shape also assures that airflow over the entire\npropeller is parallel to the surface. Thus, the air flows axially through the radiation\nshield tubes at the propeller tips.\n19.3.2\nPressure\nThe Airsonde pressure transducer is a variable capacitance aneroid cell consist-\ning of a square ceramic substrate with the aneroid capsule bonded symmetrically to both\nsides. A metalized area of the ceramic substrate forms one plate, and the capsule forms\nthe other plate of the sensing capacitor. Hence, the sensing capacitor is inside the cell\nwhere the dielectric is an unchanging vacuum, resulting in a small and rugged sensor. A\nsimilar pressure sensor has been in use at NCAR for several years (Pike and Bargen, 1976).\nThe cell is 3.18 cm on a side and 0.76 cm thick. It has a capacitance of 10 pF at\n1,000 mb. Its sensitivity is 0.03 pF/mb.\nUnlike the dry- and wet-bulb thermistors, whose calibration and interchangeabil+\nity are well defined, each aneroid cell must be calibrated individually. The calibration\nyields a curve of pressure versus capacitance that can be fitted adequately by a second-\ndegree polynomial. Four coefficients, one of which is a temperature compensation coeffi-\ncient, are provided with each Airsonde. These are placed in the computer through thumb-\nwheel switches before launch. The computer executes a program that does the curve fitting\nin real time for every frame of Airsonde data. This technique gives pressure readings in\nmillibars with a characteristic absolute accuracy of +3 mb from 1,000 to 300 mb. Accura-\ncies of +1 mb can be achieved through that pressure range if a baseline correction from a\ngood reference barometer is entered into the ground station. Under standard procedures the\nAirsonde is not calibrated for pressures less than 300 mb. Hence, flights above 300 mb may\nhave errors that are considerably greater than +3 mb, unless the Airsonde has been cali-\nbrated at those pressures and an additional correction is made to the data.\n19.4\nELECTRONICS\n19.4.1\nAirsonde\nFigure 19.6 is a block diagram of the Airsonde. The transmitter is a conven-\ntional frequency-modulated crystal-controlled circuit. It uses a voltage-controlled crys-\ntal oscillator and 9X frequency multiplication to generate 25 mW at 403.5 MHz. Temperature\nstability and narrow +5-kHz frequency deviation permit use of narrow band receivers with\nvery high sensitivity. The combination of small transmitter power and high receiver sensi-\ntivity allows a standard 9-V transistor radio battery to serve as the transmitter power\nsource. This battery is widely available, lightweight, sealed, and inexpensive.\nSensor conditioning circuitry is simple, requires little power, and uses inexpen-\nsive, readily available components. The use of precision references for both resistive and\ncapacitive sensors eliminates the need for calibration of each sonde.\nThe Airsonde has two RC data oscillators. One provides a frequency whose period\nis linearly proportional to resistance. An electronic switch acts as a timing element and\ninserts three reference resistors and then three sensing thermistors sequentially in this\nRC oscillator. The first resistor (RSYNC) has a low value that establishes a high synchro-\nnization frequency, which the microcomputer interprets as the start of a frame. The next\ntwo reference resistors (R LOREF and RHIREF) are precision components whose accuracy allows\nthe microcomputer to calibrate the data link in software during each data frame. Knowing\nthe values of these two reference resistors (10 kS2 and 100 k(2), the microcomputer can\nmeasure the resistance of three subsequent thermistors (RTINT, RTDRY, and RTWET) to an\naccuracy of 1%, from which it can compute temperature to +0.2°C, the inherent thermistor\naccuracy. The circuit has particular advantages in psychrometry because both dry- and wet-\nbulb sensors use exactly the same measurement circuitry separated in time by 1 S. The only\nerror sources in the circuitry that can contribute to a differential error are switch re-\nsistance differences and digitalization errors in data processing. The electronic switches\n113","RSYNC\nRC\nWW\nOSC.\nC\nR LO REF\nww\nAntenna\n-\nR HI REF\nWW\nR\nTINT\n+WV\nFrame\nControl\n403.5 M Hz\nR- DRY\nOSC.\nLogic\nXMTR\nww\nR WET\nCrystal\nC\nREF\nRC\nOSC.\nC\nPRES\nFigure 19.6. Block diagram of an Airsonde.\nare contained in a single, mass produced, integrated circuit. The typical ON resistance of\nthese is matched within a few ohms, an insignificant difference.\nA second RC oscillator uses a CMOS gate as the frequency source. It switches\nsequentially first to a stable reference capacitor (CREF) and then to the aneroid pressure-\nsensitive capacitor (CPRES). The ratio of these two frequencies is proportional to pres-\nsure. The thermistor that measures internal Airsonde temperature (RTINT) is mounted on the\npressure sensor, and its temperature is used by the microcomputer to correct the pressure\nmeasurement for the temperature coefficient of capacitance of the aneroid cell.\n19.4.2\nGround Station\nThe Airsonde-Tethersonde ground station (Fig. 19.3) is designed for the field\nenvironment. Mounted in an aluminum suitcase it is portable and ruggedly constructed. All\nelectronics, including the four receiver modules, are installed on one 712-in X 912-in\nprinted circuit card that is mounted on six standoffs to the aluminum front panel. This\nconfiguration is easy to service and transport.\nThe ground station can be logically divided into analog and digital sections, as\nshown by Fig. 19.7. The analog section includes the FM receiver, audio active filters, and\nphase-locked loops (PLL). One PLL is tuned for 500 + 125 Hz. This 500-Hz PLL is used with\nthe Tethersonde continuous analog channel and has no function with Airsonde operations. A\nsecond PLL, tuned for 2,500 Hz, acts as a bandpass filter with excellent signal-to-noise\nratio performance for Airsonde or Tethersonde data. It converts the sine wave signal to a\nsquare wave for input to the 16-bit frequency counter.\nThe 8080-A microprocessor and associated memory and peripheral integrated cir-\ncuits form a general purpose microcomputer. All system software resides in memory where it\nis available whenever the system power is turned on.\n114","Antenna\nAnalog\nO\nOutput\nProgramable\nActive\n403.5\nMHz FM\nFilter and\nFrequency\nRCVR\nPLL-2500 Hz\nCounter\n16 BIT\nActive\nData\nFilter and\nPLL-500 Hz\nA\nChart\n8080A\nRCDR\nDigital Display\nO\nMicroprocessor\nB\n199.9\nAnalog\nOutput\n20 MA\nAudio\nTTY, CRT\nor Hand\nCassette\nRecorder\nHeld Keyboard\n9\n9\nRS-232C\nThumbwheel\n12 VDC\nSwitches\nGP I/O\nHP 97\n16 Bidirectional\nPrinter/\n+ 12 V\nData\nCalculator\n- 12 V\nPower\nLines\nConverter\n+ 5 V\n5 V\n-\n115 VAC\nFigure 19.7. Block diagram of an Airsonde-Tethersonde ground station.\nThe ground station displays and stores Airsonde data in various ways. The prim-\nary display is a 31-digit light-emitting diode (LED) display. All data are displayed in\nreal time. One of seven individual LEDs also lights above an engraved legend that identi-\nfies the parameter currently being displayed and gives its meteorological units.\nHardcopy records can be printed on ASR-33 teletypewriter or HP-97 printing cal-\nculator (see Table 19.1). The same records can be displayed on most common CRT terminals\nand line printers. The standard HP-97 calculator has been modified for this application by\na small printed circuit card to give the microcomputer access to various storage registers\nin the calculator. The microcomputer sends data to HP-97 storage registers and initiates\nexecution of programs stored in the programmable HP-97.\nPermanent storage of data in a form readable by external computers is provided by\nmicrocomputer circuitry that controls standard audio magnetic cassette recorders. The Sony\nTC-142 gives excellent performance and is battery powered. Digital data are converted into\na series of discrete audio tones for audio recording. A standard cassette will record\nseveral hours of Airsonde or Tethersonde data. These data may be played back into the\nground station at any time for conversion to other computer-compatible media. On playback\nthe data are converted to the same format as real-time data, so all peripherals that are\nused with real-time data will work without change on recorded data.\n115","19.5\nDATA CONSISTENCY TESTS\nTo determine the consistency of the overall data processing subsystem during\nflight, the wet-bulb thermistor was replaced by a precision reference resistance equivalent\nto a 25.0°C wet-bulb reading. During the course of a flight from 843 mb to 314 mb, the\naverage wet-bulb temperature reading was 24.94°C, and the standard deviation of the values\nwas 0.05.\nIn a second flight test, the wet-bulb thermistor was left bare so that it was\nsampling dry-bulb temperature. The two sets of dry-bulb temperatures were compared for\ntemperatures ranging from 27°C at the surface to -5° at 550 mb. The mean difference was\n0.08°C, and the standard deviation of the differences was 0.04, which is within the speci-\nfications for interchangeability of the thermistors.\n19.6\nREFERENCES\nBindon, H. H. (1965) : A critical review of tables and charts used in psychrometry. In\nHumidity and Moisture, Measurement and Control in Science and Industry, Vol. 1,\nRobert E. Ruskin (ed.), Reinhold, New York, pp. 3-15.\nMorris, A. L., D. B. Call, and R. B. McBeth (1975): A small tethered balloon sounding\nsystem. Bull. Am. Meteorol. Soc. 56:964-969.\nPike, J. M. and D. W. Bargen (1976): The NCAR digital barometer. Bull. Am. Meteorol. Soc.\n57:1106-1111.\n116","20. THE TETHERSONDE SYSTEM\nAlvin L. Morris\nAmbient Analysis, Inc.\n3300 Arapahoe Ave.\nBoulder, Colorado, U.S.A.\nDavid B. Call\nAtmospheric Instrumentation Research, Inc.\n220 Central Ave.\nBoulder, Colorado, U.S.A.\nINTRODUCTION\n20.1\nA small tethered balloon system, developed at the National Center for Atmospheric\nResearch (NCAR), has been described by Morris et al. (1975). The Tethersonde TM system,\nsuccessor to the NCAR system, is similar to it in many ways. Probably the most significant\ndifference to the user is the treatment of data in the ground station. The Tethersonde\nModel TS-2A described here provides analog data quite similar to those provided by the NCAR\nsystem; it also provides digital data in conventional meteorological units.\nA Tethersonde system ready for flight is shown in Fig. 20.1. The principal\ncomponents of the system are (1) an airborne sensor package, (2) an aerodynamically shaped\nballoon (blimp) that carries the sensor package aloft, (3) a variable-speed - reversible\nelectric winch used to control tether line, (4) a ground station, and (5) several items of\nancillary equipment. The components of a Model TS-2A system, excluding the balloon but\nincluding a modified HP-97 printing calculator, are shown in Fig. 20.2.\nFigure 20.1. Tethersonde system ready\nfor flight. The balloon and sensor\npackage fly better if a rigid spacer\n(not shown) is placed between the\nsuspension lines at about the level\nof the lowest part of the bottom tail\nfin and tied to the tail fin. The\nproperly inflated 3.25 m³ balloon is\nabout 5 m long.\n117","Figure 20.2. Tethersonde system, in-\ncluding winch, ground station with\nthe sensor package in its cradle, and\nmodified HP-97 printing calculator.\nThe case containing the ground sta-\ntion is 24 X 47 X 67 cm. The mass\nof the winch is 20 kg; the mass of\nthe ground station and sensor package\nis 11.5 kg.\nDuring operation, the tethered balloon lifts the sensor package, which samples\npressure, temperature, wet-bulb temperature, and wind direction and wind speed in its\nnormal operational mode. With additional, attachable sensors, ozone, carbon monoxide, and\nthe temperature structure parameter CT have also been measured by the Tethersonde system.\nSensed values are transmitted to the ground station through two data channels on\nFM-FM telemetry using a carrier frequency of 403 MHz. One of the data channels carries\ncontinuous data from a selectable sensor; the other uses a time multiplex format to carry\ndata from one to eight sensors.\nAt the ground, the telemetry signal is converted to an analog voltage that may be\nrecorded on a strip chart recorder and to digital data that are displayed by light-emitting\ndiodes. The digital data are also available to external data storage and processing de-\nvices.\n20.2\nOPERATIONAL CHARACTERISTICS\n20.2.1\nSensor Package\nThe standard instrument package contains circuits which automatically interrogate\nthe sensors and condition sensor signals for transmission to the ground Temperature is\nmeasured over the range of -50°C to +50°C; relative pressure is measured over the range 0\nto 100 mb. Signals are scaled directly for these ranges; signals are also scaled for four\n25°C and four 25-mb ranges. By using two range scales for temperature and pressure, ade-\nquate resolution may be obtained on a small strip chart recorder without causing ambiguity.\nThe telemetry system consists of an FM, crystal-controlled transmitter and re-\nceiver. Data are transmitted at 403 MHz in two formats on separate frequency multiplexed\naudio channels. One channel uses an FM-FM PAM time multiplex format which may be recorded\nimmediately on a single strip chart or audio magnetic tape or both simultaneously. In this\nformat data quality is ensured by including high and low reference data in the recordings.\nOn the second channel, data from any one sensor are transmitted continuously in FM-FM so\nthat spectral information to 10 Hz can be telemetered.\nA data frame in the time multiplex format consists of a wide sync pulse whose\namplitude is full scale, followed by eight sensor channels separated by zero reference\nvalues. All sensor data are linear and are scaled in meteorological units for convenient\nchart interpretation. Standard sensor ranges are the following:\n118","Dry-bulb temperature: 25°C and 100°C.\nWet-bulb depression: 25°C.\nPressure: 25 mb and 100 mb.\nWind speed: 20 m/s.\nWind direction: 360°\nAll sensors are calibrated as part of the system using standards which are trace-\nable to NBS or are based on fundamental physical principles. Periodic recalibration and\ncertification service is available at the factory, but no baseline or reference calibration\nof any kind is required in the field. It is necessary to have a separate barometric read-\ning if absolute pressure is required.\n20.2.2\nGround Station\nThe Model TS-2A-GS ground station receives a telemetry signal from the sensor\npackage, processes the signal, and yields both analog and digital outputs. The analog\noutput may be recorded on an external recorder or on a small strip chart recorder contained\nin the ground station or on both. Digital data are displayed by light-emitting diodes.\nTwo 25-pin connectors permit the transfer of data in several modes. One provides RS-2320\nand 20-mA signal levels for cathode ray tube, teletypewriter, or an optional programmable,\nprinting calculator. The second connector is the terminus of 16 bi-directional data lines,\n8 of which are control lines, giving the user a general purpose programmable interface.\nThis connector also provides power, control, and data signals so that digital data in ASCII\nFSK may be recorded on and read from an inexpensive audio cassette recorder. All ground-\nstation functions are controlled by a built-in, 8-bit microcomputer (8080A)\nThe ground station also processes Airsonde signals as described elsewhere in this\nreport. It may be operated on 12 V d.c or 120 V a.c. (220 V a.c. option available).\n20.2.3 Winch\nThe electric winch is enclosed in a suitcase-size aluminum case that protects all\nparts, including the line, during shipping and storage. When in use, the lid of the case and\na small A-frame (which folds inside the case, Fig. 20.2) form the support for a line guide\na short distance above a second line guide on a level-wind. The level-wind assures proper\nwinding of the tether line on the winch drum.\nControls on the winch are contained in a small hand-held box at the end of a\ncable. This enables the user to stand under the balloon as shown in Fig. 20.1 while\nlaunching and recovering the sensor package. The controls consist of a switch with UP,\nDOWN, and OFF positions and a knob with which to control the speed of the drum.\n20.2.4\nAncillary Equipment\n20.2.4.1 Additional sensors\nFive of the eight sensor channels in the time multiplex format are used for\nstandard meteorological variables. The other three can be used to repeat a variable or for\nadditional sensors.\n20.2.4.2 Output devices\nThe most common devices for receiving output from the ground station are a chart\nrecorder, a modified Hewlett-Packard printing calculator, and a tape recorder. The analog\noutput is a voltage. To record it a chart recorder should respond to an input of 0 to 5 V\nand have a full-scale response time of less than 0.5 S.\n119","Digital data may be sent to a teletypewriter or a modified HP-97 printing calcu-\nlator. The modified HP-97 is capable of receiving data, making calculations, and printing\nboth the original and computed data. Since the calculator is easy to program, the user can\nreadily calculate any quantity permitted by the meteorological data from the ground station\nand the capacity of the calculator. Potential temperature and mixing ratio are two common-\nly calculated quantities.\n20.3\nSENSOR CHARACTERISTICS\n20.3.1\nTemperature-Humidity\nTemperature and wet-bulb depression are measured by thermistor networks which\nform the sensing elements of a psychrometer. Each network produces a voltage output that\nis linear with temperature. The manufacturer of the networks claims +0.15°C accuracy and\ninterchangeability, and a deviation from linearity of +0.16°C. The deviation from lineari-\nty is a known function of temperature; consequently it can be removed if desired.\nBoth the dry- and wet-bulb temperature sensors are placed along the axis of a\ndouble-walled, cylindrical radiation shield that is pointed into the wind. The temperature\nelement is ahead of the wet-bulb element in the flow, and the two are separated enough to\nprevent evaporation from the wet-bulb from affecting the dry bulb. A small fan at the rear\nof the tube aspirates the sensors. Water from a small reservoir flows along a wick and\nkeeps the cover of the wet-bulb sensor wet.\nThe circuitry in the sensor package measures temperature and wet-bulb depression;\nit does not measure wet-bulb temperature. This assures an accurate wet-bulb depression\neven when temperature or wet-bulb temperature may be changing rapidly with time. If wet-\nbulb depression is less than 5°C, the deviation from linearity of the depression never\nexceeds +0. 1°C. With a wet-bulb depression of 10°, the linearity error could reach +0.17°C.\nThe time constant (i.e., the time for the sensor to reach 63% of a step change in\ntemperature) of the dry-bulb sensor is about 5 S in the aspirated psychrometer. The time\nconstant of the wet-bulb sensor is believed to be about 15 S, but this value is not well\nestablished.\nTests under steady-state conditions have shown the Tethersonde psychrometer to be the\nequal of any good Assmann psychrometer.\n20.3.2\nPressure\nPressure is measured by a barometer that is similar to the NCAR digital barometer\ndescribed by Pike and Bargen (1976). The barometer is also essentially the same as the one\ndescribed in the companion paper on the Airsonde system. In the Tethersonde system, how-\never, pressure measurements are relative. By using a potentiometer in the sensor package,\npressure output is adjusted to read zero at the ground. After launch the output is the\ndifference from surface pressure rather than the absolute pressure.\n20.3.3\nWind Speed\nA three-cup anemometer mounted on top of the sensor package turns a small tachom-\neter generator. According to the anemometer manufacturer, the threshold is 0.4 m/s, the\ndistance constant is 2.4 m, and the voltage output is directly proportional to wind speed.\nWind tunnel tests of the anemometer on a sensor package indicate that the body of the\npackage does not affect the calibration. The response of a cup anemometer to a wind veloc-\nity vector that is not normal to the axis of rotation is such that tilting of the axis in\nhorizontal flow has little effect if the tilt angle is 15° or less. This response is\nsummarized by Moses (1968). The tilt of the vertical axis of the anemometer on the sensor\n120","package is difficult to observe, but except for brief spells of turbulence it is generally\nless than 15°.\n20.3.4\nWind Direction\nThe balloon is used as a wind vane. When it is tethered at the nose, fully\ninflated, and the sensor package is suspended just in front of the tail fins, the balloon\nheads into the wind. This behavior has been verified by tying a light streamer to the\ntether line a short distance below the balloon and comparing its orientation to that of the\nballoon. The sensor package is suspended by two lines, one from each side of the balloon.\nTo assure constant orientation relative to the balloon, a rigid spacer about a meter in\nlength is placed between the suspension lines at a distance of 1 m below the tie points on\nthe balloon. A magnetic compass in the sensor package detects the orientation of the\nballoon relative to magnetic north. The compass needle is momentarily locked in place on a\npotentiometer each time direction is sampled, and is free to find magnetic north between\nsamples. To determine true wind direction a compass deviation correction must be made.\nWind direction is difficult to determine by another method that can serve as a\ncheck on the direction measured by the Tethersonde system. Comparisons made with tower\ndata and careful visual checks suggest that in smooth air the Tethersonde indicates true\nwind direction to within 5°.\n20.4\nELECTRONICS\n20.4.1\nSensor Package\nThe TS-1A sensor package circuitry is divided into five major sections: (1)\nvoltage regulator and battery, (2) sensors and conditioning circuitry, (3) analog multi-\nplexer, (4) voltage controlled oscillators and filters, and (5) FM transmitter (Fig. 20.3).\n20.4.1.1 Voltage regulators and battery\nThe sensor package is powered by a 12-V, 500 mA-h, nickel-cadmium rechargeable\nThe battery voltage varies from 13.6 V at full charge to 10.5 V, the recommended\nbattery.\nlow discharge point.\nThree regulated voltages are provided in the sensor package. These are 7 V +\n0.01 V, 3 V + 0.01 V, and 9 V + 0.25 V. The 7-V regulator is the primary reference, and\nboth the 3 V and 9 V refer to this voltage.\n20.4.1.2 Sensors\nBoth temperature and wet-bulb temperature are sensed with bead thermistors. Each\nbead is a composite of two nonlinear thermistors. The composite, with a precision resistor\nnetwork, produces a voltage that varies linearly with temperature. The voltage from the\ntemperature sensor is amplified and scaled for direct input to the analog multiplexer. The\nvoltage from the wet-bulb sensor is compared electronically with the temperature sensor\nvoltage, and the difference is scaled and amplified for input to the multiplexer.\nThe anemometer cups .drive a small d.c. generator whose voltage is linearly pro-\nportional to wind speed. This voltage is amplified and scaled for input to the multiplexer.\nWind direction is sensed by an electronically actuated magnetic compass as de-\nscribed in section 20.3.4. The compass consists of a circular potentiometer element, a\nwiper mounted on a small bar magnet, and a coil surrounding the magnet. The Earth's mag-\nnetic field aligns the bar magnet and wiper. Current is passed through the coil, and the\n121","DRY\nAND\nWET\nBULB\nTEMP\n403MHZ\nPRESSURE\n(ANEROID)\n2500Hz\nXMTR\nVCO\nWIND\nSPEED\nSPARE\nCONTIN-\nUOUS\nCHANNEL\n500Hz\nVCO\nWIND\nDIRECTION\n+7.00v\nPOWER\n+3.00v\nSUPPLY\n+9.00v\nHI\nLO\nREFERENCE\nFigure 20.3. Circuitry of Tethersonde.\nlarge magnetic field created causes the wiper to contact the potentiometer element produc-\ning a voltage linearly proportional to package orientation.\nPressure is sensed by an aneroid barometer. The transducing element is an aner-\noid capacitor of special design (Pike and Bargen, 1976). This capacitor is a timing ele-\nment for an RC oscillator. A second fixed capacitor is also used as the timing element in\nthe same RC oscillator. The two capacitors are switched in alternately. The ratio of the\nresultant frequencies is proportional to pressure. The pressure transducer produces a d. C.\nvoltage that varies linearly with pressure. This voltage is compared electronically with\nthe voltage from a \"zero\" potentiometer, and the difference is scaled for pressure change\nfrom the initial setpoint.\n20.4.1.3 Analog multiplexer\nA 10-channel analog multiplexer and associated timing logic generate the Tether-\nsonde frame format. A frame consists of 20 time-clock periods. The frame starts with three\nperiods of high reference. The eight data channels follow, each one period long and pre-\nceded and followed by a one-period low reference.\nA unique automatic scale expansion circuit works in combination with the multi-\nplexer logic to give a 4:1 gain in the temperature and pressure sensor outputs. The cir-\ncuit automatically switches the reference at 25%, 50%, and 75% of full scale to give four\ntimes the normal resolution for chart record interpretation.\n122","20.4.1.4 Voltage-controlled oscillators (VCO)\nThe Tethersonde transmits data on two audio channels. These channels are fre-\nquency multiplexed to modulate the RF carrier. Two VCOs are controlled by the voltage on\nthe analog buss. One VCO oscillates at a nominal 500 Hz + 75 Hz and is used to transmit\ncontinuous data from any individual sensor. The other VCO oscillates at 2500 Hz + 375 Hz\nand is used to transmit time multiplex data on the analog bus. It carries all the informa-\ntion processed by the ground station microcomputer.\nOutput from each VCO is a square wave. The fundamental frequency is extracted\nfrom each waveform before frequency multiplexing by two low-pass active filters.\n20.4.1.5 FM transmitter\nA crystal-controlled RF transmitter produces 5 mW at 400-410 MHz depending on\ncrystal selected. The transmitter is referenced to a voltage-controlled crystal oscillator\n(VXCO) running at a nominal 44 MHz. The ninth harmonic of the VXCO is generated through\ntwo stages of frequency conversion. The first tripler runs at about 134 MHz and the second\nat about 403 MHz. The final stage is a power amplifier at 403 MHz and a buffer for the\nmonopole antenna.\n20.4.2\nGround Station\nThe ground station is the Model TS-2A-GS, which is identical to the ground\nstation described in Chapter 19 on the Airsonde system. The discussion of ancillary equip-\nment such as the printing calculator and the tape recorder contained in that chapter is\nalso pertinent here.\nTable 20.1 lists typical calculator printouts. Ground station software permits\nevery n-th data frame to be sent to the calculator whereas every frame is stored by the\ntape recorder. Thus, for example, a 10-s frame rate may be chosen, and every third frame\nmay be sent to the calculator. It then has 30 S to calculate and print a data frame, time\nenough to produce a printout like that shown in Table 20.1 (left). Since every frame is\nrecorded on tape, and since on playback the ground station can be programmed to send taped\ndata to the calculator at any desired rate up to 99 S per frame, the calculator can do\nextensive postflight calculations with every data frame. The real-time calculations are\noften found to be adequate, but in any event they provide information with which to make\noperational decisions during flight. Then if greater vertical resolution is needed or if\nadditional calculations are desired, the tape record can be used.\nTable 20.1. Typical output from the TS-1A-PC printing calculator\nNot-calculated printout*\nCalculated printout\nVariable\nPrintout\nVariable\nPrintout\nElapsed Time (min)\n1.8\n***\nTime (min)\n9.0505\nPrel (mb)\n8.4\n***\nP (mb)\n838.2\n***\nT (°C)\n25.2\nZ (m)\n121.5\n***\nAT (°C)\n11.9\nT (°C)\n23.2\nMag Dir (deg)\n321.6\n***\nRH (%)\n26.6\n0.6\n***\nU (m/s)\nW (g/kg)\n5.7\nBV (%)\n92.7\n***\nTrue Dir (deg)\n112.1\n***\nU (m/s)\n2.7\n***\nO (k)\n311.7\nBV (V)\n12.3\n***\n*Printout without calculations, but with the order of the variables changed from\nthe order in which they are received at the ground station.\n123","20.5\nREFERENCES\nMorris, A. L., , D. B. Call, and R. B. McBeth (1975): A small tethered balloon sounding\nsystem. Bull. Amer. Meteor. Soc. 56(9):964-969.\nMoses, H. (1968) : Meteorological instruments for use in the atomic energy industry. In\nMeteorology and Atomic Energy, ch. 6, David H. Slade (ed.), USAEC.\nPike, J. M., and D. W. Bargen (1976) : The NCAR digital barometer. Bull. Amer. Meteor.\nSoc. 57 (9):1106-1111.\n124","21. TETHERED BALLOON PROFILER SYSTEM\nK. Stefanicki\nInstitute of Meteorology and Water Management\nDivision of Aerology\nWarsaw, Poland\n21.1\nINTRODUCTION\nTo gather more meteorological data from the boundary layer for the Institute of\nMeteorology and Water Management, a simple and inexpensive sounding system for heights up\nto about 1 km was put into operation. Figure 21.1 shows the instrumentation package\nused in the BLIE.\nCOMPONENTS OF THE SYSTEM\n21.2\n21.2.1\nRadiosonde\nTable 21.1 lists the characteristics of U.S.S.R.-made radiosonde A-22-IV with\nredesigned pressure element, an additional wind sensor, and automatic switch for PTU and W\nsignals.\nFigure 21. 1. Instrumentation package\nused with tethered balloon\nin the BLIE.\n125","Table 21.1. Radiosonde characteristics\nParameters\nCharacteristics\nPressure\nTemperature\nHumidity\nWind speed\nSensors\nAneroid\nBimetal\nOrganic\nCup anemometer\nMeasuring\n1050 to 700 mb\n-40 to +40°C\n10% to 100%\n1.5 to 10 m/s\nrange\nResolution\n1.5 mb\n0.5°C\n2%\n0.1 m/s\nData rate\n4/min\n4/min\n4/min\n4/min\nCoding\nMorse\nPulse/10 S\nFurther information about the radiosonde is presented below:\nTransmitter frequency: 400 + 5 MHz.\nPower supply: 4.5-, 9-, and 210-V batteries.\nVentilation: Natural if wind speed is >2 m/s, artificial if wind speed is <2 m/s;\nhorizontal ventilation duct.\nFastening: Metal circular frame with shock absorbers.\nRadiation shield: Two shields, metal and fiberboard.\nWeight: 3.0 kg.\n21.2.2\nTethered Balloons and Winch\nBalloon Delacoste (made in France) has a volume of about 12 m³ and a height limit\nof about 1 km and is filled with helium. This balloon may not be used when wind velocity\nexceeds 4 m/s at the ground and 10 m/s aloft.\nBalloon Zodiac (made in France) has a volume of about 20 m³ and a height limit of\nabout 1.5 km and is filled with helium. This balloon may not be used when wind velocity\nexceeds 4 m/s at the ground and 15 m/s aloft.\nThe winch (our own design), which operates electrically, has two cable speeds,\n1\nand 2 m/s. It is equipped with a hand brake, a cable length counter, and an azimuth\ndisc. For the BLIE the smaller 7-m3 balloon and winch described in Chapter 20 were used.\n21.2.3\nAcquisition and Processing Equipment\nThe equipment consists of a receiver, a pulse counter, and a calculator, whose\ncharacteristics are listed below:\nPower requirements: 220 V, 50 (60) Hz.\nPressure, temperature, and humidity: Audio-Morse signals, recorded manually.\nWind speed: Pulse counter, recorded manually.\nProcessing: With the aid of a calculator, height is computed either with the baro-\nmetric formula or by radar tracking; the height of the lowest levels can\nbe determined by cable length.\n126","SOUNDING PROCEDURE\n21.3\nThe radiosonde is mounted on a tethered balloon. Measurements are made during\nballoon stops at selected levels, both during ascent and descent. Before launch and just\nafter sounding completion, a ground check of the radiosonde is required. The measurements\nat each level take about 3 min.\n21.4\nRESULTS\nThe results are presented in the form of computer-generated tables and graphs\n(parameter vs. height) . Time required to process the data is about 1 h. Data accuracies\nare listed below:\nHeight: +15 m.\nTemperature: +0.5°C.\nHumidity: +5%.\nWind speed +0.2 m/s.\nWind direction: +20° (rough estimation based on determination of balloon position\nwith respect to the north using a special attachment at the winch)\n127","22. BOUNDARY LAYER PACKAGES FOR TETHERED BALLOON\nM. Hayashi and 0. Yokoyama\nNation Research Institute for Pollution and Resources\nUkima, Japan\n22.1\nINTRODUCTION\nThree types of boundary layer patkages for balloon-borne measurements were\ncompared in the BLIE. Figure 22.1 shows the prototype, Meisei Denki, model CBS-W-5. The\nother two are variations of the prototype: (1) the simplest version, Makino (Fig. 22.2),\nand (2) the fully equipped version, Kaijo (Fig. 22.3). Although their appearances differ,\nthe variations in sensors are minor. The packages use the same cup anemometer. Meisei\nuses a bi-directional vane and detects the angle of the vane by the optical method; the\nothers have a vertical vane and detect the angle by a contactless potentiometer (see\nChapter 20). Kaijo has a hot-wire anemometer and a thermocouple to measure fine fluctu-\nations in wind speed and temperature.\n22.2\nSENSORS AND DATA PROCESSING\n22.2.1 Cup Anemometer\nWind speed is detected by a small, three-cup anemometer. The cup is made of\nmolded plastic. The length of the arm is 6.5 cm, the cross-section of the cup is 2.0 cm2 2\nand the estimated moment of inertia is 450 g cm². One rotation produces eight pulses on\n,\nthe photoelectric chopper. The pulses are shaped into square waves and mixed with other\nsignals through subcarrier (voltage-controlled) oscillators.\n22.2.2\nVane\nVertical and lateral wind direction fluctuations are detected by a bi-directional\nvane. It has four rectangular flat plates (8 X 9 cm) made of light wood (balsa) with\nplastic support. The vertical and lateral angles of the vane are detected by using an\noptical mechanism for reducting the friction.\n22.2.3\nCompass and Mean Wind Direction\nThe azimuth of the instrument is detected by a magnetic compass. The angle of\na small rotating magnet in an oil box is detected by an optical servomechanism.\n22.2.4\nThermometer\nTemperature is detected by a fine platinum wire of 100 S. The temperature\nfluctuation is detected by a thermocouple of copper-constantan in the Kaijo instrument.\nThe standard temperature is given by a transistor thermometer with a time constant of\n3 min.\n22.2.5\nHumidity\nWe do not yet have a suitable humidity sensor. The gauze-covered wet-bulb\nthermometer yields mean humidity. A lightweight hygrometer with fast response and low\nelectric power consumption is needed.\n128","VERTICAL\nVANE\n0 40mm\nBI-VANE\nO\nCUP\nANEMOMETER\nTHERMOMETER\no\nTHERMOMETER\no\nCUP\nANEMOMETER\n0\n100\nmm\nFigure 22. 2. The simplest version\nFigure 22. 1. Prototype boundary layer\nof the prototype.\npackage for balloon-borne measurements.\nCUP\nANEMOMETER\nVERTICAL\nVANE\nHOT\nWIRE\nBATTERY\nRECORDER\nTHERMOMETER\nCOMPASS\nTHERMO -\n0 20mm\nCOUPLE\nFigure 22.3. Fully equipped version of the prototype.\n129","22.2.6\nHeight\nThe height of the instrument package is given by released line length with\nallowance for elevation angle to the balloon when the wind speed is high.\n22.2.7\nData Processing System\nThe electronic data processing system in the package is diagrammed in Fig. 22.4.\nThe signals from each sensor are converted to frequency modulated signals according to the\nIRIG standard and then mixed together. The mixed FM signal is transmitted by frequency-\nmodulated UHF carrier at 404.5 MHz. However, wireless transmission of this type is per-\nmitted only for experimental tests.\n22.2.8\nRecording System\nThe mixed signal is recorded on an audio microcassette tape recorder, Sony M-200,\nfor practical use (Hayashi et al., 1974). To avoid the WOW and flutter of the tape re-\ncorder, a standard frequency (3 kHz) is recorded simultaneously. This is used as an au-\ntomatic frequency controller when the signal is reproduced. The recording duration is\n30 min. The recorded signal is reproduced in the laboratory, discriminated by filters,\nand reduced to the original signal through a frequency-voltage converter.\n22.2.9\nHarness\nThe instrument package is hung on the mooring ropes below the center of the cap-\ntive balloon shown in Fig. 22.5. The balloon is tear-drop shaped, with four fins at the\nrear. The volume of the balloon varies from 20 to 75 m³. The mooring rope is nylon fish\nline 6 mm in diameter, 0.0142 g/m, and 500 kg test. The instrument is supported by a\ngimbal bar so that all sensors are exposed to the wind. For the BLIE, the 7-m3 balloon and\nwinch described in Chapter 20 were used.\n22.3\nCALIBRATION\n22.3.1\nCup Anemometer\nThe characteristics of the cup anemometer have been studied in a wind tunnel and\nin the field by Hayaski and Miyake (1973). The equation of motion of a cup anemometer is\nI dt dw + F = M,\nwhere I is the moment of inertia, w the angular velocity, F the friction, and M the torque\nof the rotating assembly of the cup. The torque is assumed to be given by the difference\nin the drag of a pair of cups:\n-\n,\nwhere U is the wind speed, R the length of the arm, p the air density, S the cross sec-\ntion of the cup, N the number of cups, C_ and C+ the drag coefficients of the cup along and\nagainst the wind, and a the variability of the torque of the entire cup assembly during a\ncomplete revolution. If N = 2, a varies between 0 and 1, but for three- and four-cup ane-\nmometers a is nearly uniform and equal to or slightly less than 1. The drag of the rota-\nting system is divided into static and dynamic terms as follows:\n130","CUP ANEMOMETER\n000\n1700HZ\nBI-VANE\nANALOG\nWIND SPEED\nMEAN\nTO\nDATA\nVARIANCE\nDIGITAL\nANALYSER\nVERTICAL ANGLE/CONVERTER\nSPECTRUM\n730HZ\nRECORDER\nREPRODUCER\nCHITAC\nFLUX\n(TEAC\nCOSPECTRUM\nHORIZONTAL ANGLE\n-10\nDP-5000X\n960HZ\nTEMPERATURE\nCOMPASS\nm\n2300HZ\nTHERMISTOR\nSUB CARRIER\nOSCILLATOR\nLABORATORY\nFIELD\nFigure 22.4. Data-processing system for the balloon package.\n22 .5. The instrument package\nFigure\nmounted under a captive balloon.\n131","6\n5\n2\nRPS\n4\n3\n2\nI\n0\n0\n2\n3\n4\n5\n8\n6\n7\nWIND SPEED (m/s)\nFigure 22.6. Calibration of cup anemometer in wind tunnel. Tunnel\nwind speeds were measured by a sonic anemometer calibrated by a\nPitot tube.\nF = BO + B1W .\nThe fluctuation of wind speed, u, is smaller than the mean wind speed, :\nand\n+\n,\nwhere E gives the order of the perturbation.\nThe zero-order equation gives the calibration curve of the cup anemometer. The\nrelationship between the wind speed and the rotation of the cup assembly was tested in\nthe wind tunnel. The Pitot tube was used as the standard instrument for measuring the flow\nvelocity. At lower wind speeds, since the output of the Pitot tube is difficult to read,\nwe used a sonic anemometer, Kaijo model PA-100, as our standard instrument. The result of\nthe test is shown in Fig. 22.6. The starting wind speed is about 10 cm/s.\nThe transient response of the cup anemometer was tested in the wind tunnel. The\nfirst-order perturbation gives the linear response for wind speed change. The response is\ngiven by a distance constant\nL =\naNpR2SVc_C+\n132","10\nUSAT SAT\n(m/s)\nG\n5\nS\nFigure 22.7 Comparison of mean wind\nY\nspeed measured by a cup anemometer\nX\nand a sonic anemometer in turbulent\n&\natmosphere. The plotted letters\nidentify different runs.\n0\n5\n10\n0\nUCUP (m/s)\nThis response is about 4.5 m for this cup anemometer. The second-order perturbation shows\nthe nonlinear response of the cup anemometer, i.e., , the over-run (rotation) of the cup\nassembly. This is one of the most distinctive features of a cup anemometer, i.e., that\nit overestimates the mean wind speed in turbulent air flow. The cup anemometer calibrated\nin the wind tunnel was compared with the sonic anemometer, Kaijo model TR-32, in the real\natmosphere. Both instruments were mounted on top of a 13-m tower. The overestimate of the\ncup anemometer amounts at most to 7%, as shown in Fig. 22.7.\nThe relationship between the wind speed, U, and the cut-off frequency, Ec is\nobtained by comparing spectra. The cut-off frequency is U/2L. The comparison gives the\nfrequency response function of the cup anemometer, as shown in Fig. 22.8. The turbulent\nintensity measured by the cup anemometer is about 83% of that measured by the sonic anemom-\neter, as shown in Fig. 22.9.\n22.3.2\nVane\nThe transient response of the vane was tested by Yokoyama (1969) with a wind\ntunnel. Figure 22.10 shows an example of the time response of the vane to a step-function\ndirection change. The response of the vane angle, 0, can be represented by the following\nequation of simple damped oscillation:\ndt2 d20 2-2wn5 - dt dO - 20 = F(t) ,\n,\nwhere Wn is the natural angular frequency of the vane, S is the damping ratio (the ratio\nof the actual damping to the critical damping), t is the time, and F (t) is a time-dependent\nforcing function. The damping ratio, 5, and natural frequency, Wn, are obtained from the\nmeasurements of the time response to a step-function direction change for various wind\nspeeds by use of a solution of the equation for the case of 5 < 1. The distance constant\nof the vane, U/wn5, is used as an index of the response characteristics and regarded as\na constant for high wind speeds. It is approximately 1.6 m for this type of vane. An\nexample of the frequency response for typical wind speeds is shown in Fig. 22.11.\n133","10\n6\n2,\n43\nG2(f) 1\nC_C\n4C\n40\nC\n65\nA\n4\nATOA\nD\n4\n2\nI\n6\n53\nI\nD\n0.1\n6\n3\n4\n4\n0,01\n0.001\n0.01\n0.1\n1\n10\nfc\nFigure 22.8. The frequency - response function as a ratio of power\nspectra from the cup and those of the sonic anemometer. The\nplotted letters and numbers identify different runs.\n0.5\nJ\n&\nL\nSAT\nR\nT\nWU\nM,H\nN Q\nFigure 22. 9 .\nComparison of /U as\nO/IU\nmeasured by cup and by sonic anem-\nometer. The plotted letters iden-\ntify different runs.\n0\n0.5\nCUP\n134","Time\n2\n1\n45\n5\n0.5\n5.0\n0.1\n1.1\n0.2\n0\n0\n5.0\n-90\n0.1\n1.1\nQ\n180\n5\n10\n0.5\n1\n0.1\nn (Hz)\n1 S\nFigure 22.11. Frequency response of\nFigure 22.10. Example of the measured\nthe vane for various wind speeds\ntime response of the vane to a step-\n(G is the ratio of amplitudes and\nfunction direction change. (Mean\n0 is the difference of the phases.\nwind speed is 3.0 m/s and angle of\nEntries are wind speed in m/s.)\nattack is 45.0°.)\nOUTPUT FORMAT\n22.4\nThe raw tape recorded data are contained within an FM multiplexed signal in the\nIRIG standard. The signal is separated by a discriminator into separate signals of each\nsensor. The output range depends on the discriminator. The discriminator used in the BLIE\nis for the simplest boundary layer package. It has only four channels, one each for wind\nspeed, elevation angle, and dry- and wet-bulb temperatures. The range of the voltage is\nfrom 0.0 to 1.0 V. The corresponding outputs are 0.0 to 10.0 m/s for wind speed, o -45 to\n+45 degrees for elevation angle, and one of the ranges -10°C to +10°C, 0°C to 20°C, 10°C to\n30°C, or 20°C to 40°C, for wet- and dry-bulb temperatures. To obtain the signals from the\nother two sensors, hot wire and thermocouple, we need a discriminator with more channels.\nREFERENCES\n22.5\nHayashi, M., and M. Miyake (1973): Some characteristics of cup anemometers. Kogai\n(Japan) 9:53-61.\nHayaski, M., 0. Yokoyama, H. Yoshikado, and K. Nemoto (1974): A boundary layer package\nwith tape recording system inside. Tenki (Japan) 21:45-47.\nNakajima, S., (1967): On the meteorological observation in the lower atmosphere by a\ncaptive balloon. Weather Serv. Bull. (Japan) 34:1-65.\nOotsuka, S., N. Shishido, N. Honda, S. Nemoto, S. Koinuma, M. Hayashi, and M. Miyake\n(1975): Observations of the planetary boundary layer by tethered ballons and lower\ntropospheric radionsonde. Scientific Report of the Fourth AMTEX Conference,\n26-29 September 1975. AMTEX Report No. 8, Tokyo, Japan, pp. 70-73.\nYokoyama, 0. (1969): Measurements of wind fluctuations by a vane mounted on the captive\nballoon cable. J. Meteorol. Soc. Japan 47:159-166.\n135","23. NCAR BOUNDARY PROFILER SYSTEM\nRobert B. McBeth and Steven Semmer\nNational Center for Atmospheric Research\nBoulder, Colorado, U.S.A.\n23.1\nINTRODUCTION\nThe NCAR Boundary Profiler (BP) system is a small tethered-balloon system (Morris\net al., 1975) providing the user with five meteorological parameters: dry-bulb tempera-\nture, wet-bulb temperature, pressure, wind speed, and wind direction. Data information is\ntransmitted, in a time multiplex format, to a ground station, where it is recorded on\nmagnetic tape for later processing and on a strip chart recorder for real-time analysis.\nThe system is portable and can be operated by one person.\n23.2\nDESCRIPTION\nThe BP system consists of a sensor package attached to an aerodynamic balloon, a\ntether line controlled by a winch, and a ground station.\nThe balloon's approximate dimensions are length, 4.8 m; maximum diameter, 1.4 m;\nvolume, 3.25 m³ It has a lifting capability of 1.9 kg at sea level. In calm weather the\nballoon has been flown to heights of 600 m. With its aerodynamic shape, the balloon acts\nas a wind vane and is used in computing wind direction. Because of its small size, it can\nbe flown without a special FAA waiver.\nThe winch consists of a drum wheel driven by a 1/3-hp motor. The tether line,\n100-1b test nylon cord, is wrapped around the drum wheel. The motor operates on 110 V a.c.\nAn SCR controller sets the rate of ascent and descent of the package. The operator can\nvary the rate from 0 to 3 m/s depending on weather conditions.\nThe telemetry package was purchased off the shelf. A brief description of the\npackage is given here; more detailed information can be found in the description of the\nTethersonde. The package gets its power from 12 1.22-V nicad batteries, giving an average\nflight time of 2 h. A d.c. signal from each sensor circuit is fed into a time multiplexer.\nFrom there the signal is passed on into a voltage-controlled oscillator where it is con-\nverted to a frequency in the range of 2.6 to 3.4 kHz. The data signal is then used to\nmodulate a 403-MHz crystal-controlled transmitter. The power output of the transmitter is\nabout 10 mW.\nThe ground station is made up of three parts: a receiver, an Esterline Angus\nstrip chart recorder, and a digital cassette system. The receiver picks up the 403-MHz\nsignal and passes the audio portion on to a discriminator circuit and the cassette system.\nThe audio discriminator converts the audio tone to an electrical signal ranging from 0 to\n5 V. This signal is then fed into the chart recorder to provide a real-time look at the\ndata. The audio tone going into the cassette system is filtered and passed on into a\nfrequency-detector circuit. The detector circuit determines when to take a sample of data\nand record it on tape. Between all data samples there is a down signal. The down signal\nhas a frequency outside the range of the detector so the detector will be turned off\nduring this signal and on during a data signal. The down frequency is at 2.3 kHz, and the\ndata frequencies are in a range of 2.6 to 3.4 kHz. When the detector circuit is set, a\nshort time delay takes place to allow for a clear signal, and then the data signal is\npassed on into a counter for 0.256 S. The lower eight bits of the counter become the\ndigital representation of the data sample and are recorded on tape. The frequency span of\n0.8 kHz represents a span of 205 counts. The cassette tape is then processed on a micro-\ncomputer system. The cassette system also contains a real-time - clock, and at the beginning\n136","Ground Station\nTelemetry Package\nReceiver\nTransmitter\n+12 V\nBattery\nAudio\nFilter\nDiscriminator\nVoltage\nVCO\nRegulator\nStrip Chart\nRecorder\nConditioning\nClock\nCircuit\nCassette System\nFilter\nMultiplexer\nFrequency\nCassette\nCounter\nDetector\nRecorder\nSync.\nDown\nReal-Time\nLevel\nClock\nDry T\nMicrocomputer System\nWet T\nWith Graphics\nAneroid\nPress\nZero\nWind Sp.\nWind Dir.\nFigure 23.1. Block diagram of NCAR Boundary Profiler electronics.\nof each data frame time is recorded on the magnetic tape. Figure 23.1 is a block diagram\nof the BP system.\nSENSORS\n23.3\nBead thermistors are used to measure dry- and wet-bulb temperatures. The sensors\nare mounted in a radiation shield tube and are aspirated by a small fan located at the end\nof the tube. The wet-bulb thermistor is covered by a sock, which is connected to a small\nreservoir.\nPressure is measured with an aneroid capsule. The pressure sensor is set up to\nmake a relative reading, not an absolute one. The relative reading has a total differen-\ntial range of 100 mb.\nWind speed is measured with a three-cup anemometer connected to a small d. C.\ngenerator. Wind direction is determined by using the balloon as a wind vane in conjunction\n137","Table 23.1. Sensor characteristics\nSensor\nTotal range\nSet range\nPrecision\nThermistor\n-30° to 45°C*\n25°C\n+0.5°C\nAneroid capsule\nRelative\n100 mb\n+1 mb\nCup anemometer\n0.5 to 10 m/s\n0 to 10 m/s\n+0.25 m/s\nMagnetic compass\n0° to 360°\n0° to 360°\n+5°\nand balloon\n*Six switches set temperature ranges in 25°C increments\nPressure is set at ground level relative to launch site.\nSync\n100%\n(3.4 kHz)\nWind\ndir\nDry T\nDry T\nWind\nPress\nspeed\nWet T\nWet T\n0%\nZero\n(2.6 kHz)\nDown\n(2.3 kHz)\nFigure 23.2. Data frame on strip chart recorder.\nwith a magnetic compass. The magnetic compass is a potentiometer with the compass needle\nacting as the arm of the pot. When it is time to sample wind direction an electric field\nlocks the needle to the pot windings. This gives a clean reading when a sample is taken.\nTable 23.1 gives more information about each sensor.\n23.4\nDATA FORMAT AND PROCESSING\nFigure 23.2 is an example of one data frame recorded on the strip chart. The\naverage frame duration is 30 S but can range from 20 to 40 S. The sync pulse represents\n100% or 3.4 kHz, whereas the zero pulse is 0% or 2.6 kHz. Data are transmitted in the\nfollowing order: (1) sync, (2) dry-bulb temperature, (3) wet-bulb temperature, (4) pres-\nsure, (5) zero, (6) dry bulb, (7) wet bulb, (8) wind speed, and (9) wind direction. The\nuser can change this sampling order. The down signal is used to separate each channel\nsample from the next one. The scale ranges for each data parameter are listed in Table\n23.1. The zero reference level for temperatures can be set by the user in 10°C increments\n138","BAO/WMO\nFLIGHT (10)\n30,1979\nAUGUST\nHT/MSL\nWS\nWD\nRH\nHEIGHT\nWBULB\nDP\nPRESS\nTIME\nDBULB\n(M)\n(MB)\n(M/S)\n(DG)\n(%)\n(M)\n(C)\n(C)\n(H:M:S)\n(C)\n10.17\n1587.17\n309\n53\n8.55\n839.60\n0.00\n8:30:23\n17.21\n11.47\n53\n21.36\n1598.36\n8.58\n838.50\n0.00\n310\n17.24\n11.49\n8:30:45\n1625.88\n53\n48.88\n835.80\n0.00\n306\n11.17\n8.31\n8:31:36\n16.73\n99.01\n1676.01\n306\n48\n830.90\n2.73\n16.87\n10.55\n6.69\n8:33: 4\n148.48\n1725.48\n4.24\n332\n39\n4.33\n826.10\n17.95\n10.07\n8:34:54\n1776.40\n41\n199.40\n4.81\n332\n10.65\n5.56\n821.20\n8:36:34\n18.31\n1826.63\n322\n37\n249.63\n816.40\n4.32\n10.22\n4.16\n8:38:35\n18.55\n301.19\n1878.19\n320\n37\n3.92\n811.50\n3.27\n8:40:31\n18.27\n10.00\n34\n380.91\n1957.91\n2.51\n325\n4.27\n804.00\n8:43:28\n19.89\n10.73\n478.02\n2055.02\n258\n25\n0.61\n795.00\n1.56\n8:47:32\n21.18\n10.00\n25\n480.42\n2057.42\n1.84\n223\n0.83\n795.00\n21.89\n10.34\n9: 1:23\n1960.04\n32\n383.04\n804.00\n4.48\n298\n11.08\n4.26\n9: 7:53\n20.81\n302.90\n1879.90\n321\n29\n811.50\n4.76\n9: 9:36\n20.59\n10.31\n2.10\n251.03\n1828.03\n5.11\n326\n31\n2.33\n816.40\n19.83\n10.11\n9:10:56\n1777.62\n37\n200.62\n5.07\n321\n10.83\n5.04\n821.20\n9:12:17\n19.26\n1726.55\n320\n45\n149.55\n826.10\n4.80\n11.47\n7.32\n9:13:19\n18.65\n99.82\n1676.82\n335\n38\n5.19\n830.90\n3.10\n19.03\n10.83\n9:14:11\n0.55\n311\n42\n49.29\n1626.29\n7.28\n835.80\n9:15:12\n19.46\n11.80\nFigure 23.3. Example of data listing for a BLIE flight.\nstarting at -30°C and going up to 20°C. The user also has the ability to set a ground\nlevel reference for the pressure. Data recorded on magnetic tape have a similar format,\nexcept that no down channels are recorded and time information is placed on the tape after\neach sync signal.\nAlthough the strip chart provides a real-time look at the data, the final anal-\nysis is done with the digital cassette tapes. With the use of a microcomputer graphics\nsystem, the cassette data are transferred to a digital cartridge tape. Each frame of raw\ndata is then converted to physical units, with the sync and zero data being used for\nmaximum and minimum levels. When all data have been converted, they are interpolated to\none time point per frame, and the height, dewpoint, and relative humidity can be computed.\nThe user can now use the graphics to obtain a listing of the flight data in tabular form\nor an XY plot of time versus data. Figure 23.3 is an example of a listing of flight data.\nREFERENCE\n23.5\nMorris, A. L., D. B. Call, and R. B. McBeth (1975) A small tethered balloon sounding\nsystem. Bull. Am. Meteorol. Soc. 56: 964-969\n139","24. DETAILS OF THE EXPERIMENT\nJ. C. Kaimal and J. E. Gaynor\nNOAA/ERL/Wave Propagation Laboratory\nBoulder, Colorado, U.S.A.\nH. W. Baynton\nNational Center for Atmospheric Research\nBoulder, Colorado, U.S.A.\n24.1\nINTRODUCTION\nThe Boulder Low-Level Intercomparison Experiment commenced on schedule at\n0800 MDT on 27 August 1979. Favorable weather conditions and the absence of major equip-\nment problems contributed to a highly productive first week (27-31 August) As a result,\nno tests were run during the 3-day weekend. On 2 days during the following week (4-5\nSeptember) observations were resumed primarily for participants who needed more data.\nSome had made improvements in their sensors after the first week and were eager to see the\neffect; others simply wanted more observations.\nThe BAO tower instrumentation and associated data acquisition and processing\nsystems (see Chapter 1 of this report) were operated continuously for the entire 2 wk.\nFunctioning in a 20-min averaging mode, the data acquisition system printed out summary\nlistings of BAO data at the end of each averaging period. The listings provided a set of\ncommon reference data for comparison of all sounding systems. Although each listing was\nwithheld from the participants during the core observing periods until after the 24 h\nallowed for submission of their data, it was subsequently available for system checks and\ncalibration.\nA major problem in planning the experiment was crosstalk and interference\nbetween systems operated concurrently. Most radiosonde and tethered balloon systems used\ntelemetering frequencies that overlapped. Balloons and kites served as reflecting targets\nfor sodars, interfering with their Doppler measurements. The remotely piloted aircraft,\nbesides being a reflector, generated its own acoustic noise and used radio frequency bands\nshared by the radiosonde and tethered balloon systems. Doppler sodars are known to inter-\nfere with one another even when their operating frequencies are far apart.\nCoordinating this complex set of interactions called for optimal use of time\nsharing, spatial separation, and frequency tuning. The major crosstalk problems were\nsolved before the experiment started by planning the location of sensors in the field and\nassigning specific observing windows for each sensor. In this chapter we describe the\nexperiment and detail the specific problems and solutions, which should serve as back-\nground for interpreting the results in Chapter 25.\n24.2\nSENSORS COMPARED\nEssential information on all sensors that participated in the BLIE is given in\nTable 24.1. The numbers indicate the order in which the papers are presented in Part 1 of\nthis report. The sensors omitted from the list required unacceptable lead times for data\nprocessing. As mentioned in the Preface, participants in the BLIE were required either to\nsubmit data from each run within 24 h or to provide analog signals for sampling and pro-\ncessing in the BAO acquisition system.\n140","Table 24.1. Sensors used in the BLIE\nAffiliation\nPrincipal\nParameters*\nCountry\nSensor\nSensor\nscientist\nmeasured\nnumber\ntype\nWave Propagation Laboratory,\nJ. C. Kaimal\nU,V,W,T,T d\nU.S.A.\nTower system\n1\nNOAA, Dept. of Commerce\n(BAO)\nMeteorological Research\nJapan\nT. Hanafusa\nU,V,W,T\nSonic anemometer-\n2\nInstitute, Japan Meteor-\nthermometer\nological Agency\n(Kaijo Denki)\nVaisala 0y\nI. Ikonen\nS,D,T,RH\nFinland\nTower system\n3\n(Vaisala)\nEtablissement d'Études et de\nRemotely piloted\nT,RH,P\nFrance\nD. Martin\n4\nRecherches Météorologiques\naircraft (SAM-B)\nApproach Fish, Inc.\nC. F. Woodhouse\nS,D\nU.S.A.\n6\nKite anemometer\n(TALA)\nFederal Institute of Tech-\nSwitzer-\nP. Ravussin\nRadio acoustic\nT\n7\nnology of Lausanne\nland\nsounding system\n(RACES)\nWave Propagation Laboratory,\nR. B. Chadwick\nU,V\nU.S.A.\n8\nFM-CW radar\nNOAA, Dept. of Commerce\nWave Propagation Laboratory,\nW. D. Neff\nU,V\nU.S.A.\nBistatic sodar\n11\nNOAA, Dept. of Commerce\nAeroVironment, Inc.\nP. B. MacCready\nU,V,W\nU.S.A.\nMonostatic sodar\n12\n(AVIT)\nRadian Corp.\nM. A. McAnally\nU.S.A.\nU,V,W\nBistatic sodar\n13\n(Echosonde)\nUniversity of Uppsala\nS. Salomonsson\nMonostatic sodar\nU,V\nSweden\n14\n(Sensitron)\nXonics, Inc.\nR. L. Peace, Jr.\nU,V,W\nU.S.A.\nBistatic sodar\n15\n(XONDAR)\nNational Center for Atmos-\nR. B. McBeth\nS,D,T,RH,P\nU.S.A.\n16\nGMD-1/VIZ\npheric Research\nradiosonde\nDeutscher Wetterdienst\nE. Schöllmann\nT,Tw,P\nF.R.G\nTDFS low-level\n17\nradiosonde\nVaisala Oy\nI. Ikonen\nS,D,T,RH,P\nFinland\nCORA radiosonde\n18\nAIR, Inc.\nD. B. Call\nU.S.A.\nAirsonde radiosonde\nT,Tw,P\n19\nAmbient Analysis, Inc.\nA. L. Morris\nS,D,T,T,,P\nU.S.A.\nTethersonde profiler\n20\nInstitute of Meteorology\nK. Stefanicki\nS,T,RH,P\nPoland\nTethered balloon\n21\nand Water Management\nprofiler\nNational Institute for\nM. Hayashi\nS,E,T,T\nJapan\nTethered balloon\n22\nW\nPollution and Resources\nprofiler\nNational Center for Atmos-\nU.S.A.\nR. B. McBeth\nS,D,T,T,,P\nTethered balloon\n23\npheric Research\nprofiler\nRH - relative humidity\n- wind direction\n*U - wind component (positive from west)\nD\nP - pressure\nV - wind component (positive from south)\nT\n- temperature\nE - elevation angle\n- dew point temperature\nW - vertical wind component (positive up)\nT\nTd\n- wet-bulb temperature\nS - wind speed\nW\n141","The variables measured by the different systems were reduced to the following\ncommon parameters for comparison:\n(1) Horizontal wind component U (positive from west).\n(2) Horizontal wind component V (positive from south)\n(3) Vertical wind component W (positive upward).\n(4) Temperature T.\n(5) Dew point temperature Id\n(6) Relative humidity RH.\n(7) Height above ground Z.\nAll measurements were reported for heights corresponding to the fixed levels on the tower.\nReporting levels for radiosonde observations above tower heights were set at pressure\nlevels corresponding to 400, 500, 750, 1,000, 1,250, 1,500, 1,750, 2,000, 2,250, 2,500,\n2,750, and 3,000 m.\nThe unit of time for data comparison was a 20-min period coincident with the BAO\naveraging period. In-situ and remote sensors were expected to provide time-averaged data\ncompatible with the BAO tower profiles. For immersion sensors, which use a single instru-\nment package to probe the layer, a full ascent or descent had to be completed within the\n20-min period. When this was not possible, the period containing the most profile points\nwas used for comparison.\n24.3\nLOCATION OF SENSORS\nAssignment of sensor locations (Fig. 24.1) was based on several considerations:\nthe crosstalk problem, the availability of a.c. power, and the need for certain sensors to\nbe far from (or close to) the tower. Groups operating in shifts or flying instruments on\nthe same balloon train had to be close together for easy communication.\nMajor areas of activity centered around the tower base, anchor point B, and the\ntemporary building. Air-conditioned office trailers were provided at each of these loca-\ntions to house equipment and personnel. The circled numbers in Fig. 24.1 indicate the\nsensors occupying each trailer.\nThe electronics for the tower systems were situated in the trailer close to the\ntower to keep signal lines short. Radiosonde and tethered balloon activities were located\nnear the temporary building to be far away from the tower and its guy wires. Since by\narrangement the remotely piloted aircraft would not be operated when the balloons were\nflown, its landing strip was placed close to the balloon launch area. The installations\naround the building can be seen in Fig. 24.2.\nThe sodar antennas (see Fig. 24.3) were laid with their axes aligned E-W and N-\nS\nand their centers close to anchor point B. With this arrangement, the sampling volumes\nof the bistatic sodars and the lower levels of the monostatic sodars were close to each\nother. Their remoteness from the tower was intentional; to avoid reflections the sodars\nwere placed at a distance from the tower equal to or greater than the expected height\nrange of the devices.\nOperating around anchor point A and sometimes around anchor point C (see Fig.\n24.1), the kite anemometer was sufficiently removed from the other sensors to avoid inter-\nference. Its only potential conflict was with the remotely piloted aircraft, but this was\navoided by scheduling kite and aircraft operations at different times.\n24.4\nOPERATING SCHEDULE\nIn the initial plan three observing periods with 2-h breaks for rest and refresh-\nments were scheduled for each day:\n142","12\n15 (Rec)\n(Xmit)\n13 (Xmit)\n11 (Xmit)\n15\n(Rec) 13\nAnchor\nAnchor\nPoint\nPoint\nC\nB\nSensors\n(Rec) 11\n1 2 3\n13\n14\n15/12\n14\nElectronics\n11\nBAO\n1\nTOWER\nElectronics\n(Rec) 15\n2\n3\n13\n(Xmit)\nAnchor\n11\nPoint\n(Xmit)\nX\nA\n/\n6\nLanding\nLaunch\nStrip\nArea\nBalloon\n16 to\nN\n4\nStorage\n7\n23\n16\nTrailers\n23\n17 22 19 20\n4 21 7 18\nTEMPORARY\nScale (m)\nBUILDING\n200\n300\n0\n100\n8\nCounty Road 8\nFigure 24. 1. Locations of sensors operated during BLIE. Table 2.1 gives the key to number\ndesignations.\n143","Figure 24.2. Temporary building and launch areas for balloons and aircraft.\nFigure 24.3. Sodar antennas at anchor point B as seen from the BAO tower.\n144","Period 1 (0800-1200 MDT): Period of boundary layer growth.\nPeriod 2 (1400-1800 MDT): Period of nearly constant boundary layer depth.\nPeriod 3 (2000-2400 MDT) Period of stable boundary layer.\nAs the sensors were checked out, adjustments had to be made and the observing\nperiods extended in either direction to make room for sensors that could not be operated\nwithin the core observing periods. The basic schedule is shown in Table 24.2. The sched-\nule and the operating procedures described in this chapter were tested in a short dry run\nbeginning at 0800 MDT on 25 August.\nAccording to the schedule, the sodars were assigned separate time slots. Ini-\ntially AeroVironment and WPL sodars were operated concurrently; however, when interference\nwas suspected, the AeroVironment sodar was moved to different time slots outside the core\noperating period during Periods 1 and 2. The remotely piloted aircraft was not operated at\nnight because of the need for visual contact. The sodar schedules for Period 3 were\nrearranged to take advantage of this fact.\nTethered balloon and radiosonde operations were scheduled at different times\nwithin the observing periods. The only exception was the profiler from Poland which\ninterfered with other telemetry systems and was assigned a period outside the core ob-\nserving periods. The tethered balloon profilers were not operated at night because they\nrequired visual monitoring.\nOTHER CONSIDERATIONS\n24.5\nEffect of Tower Structure on Measurements\n24.5.1\nThe tower sensors are mounted on booms extending roughly 5 m SSE and NNW. The\nBAO sonic anemometers and the Propvanes are mounted at the ends of these booms pointing in\nopposite directions. Since the velocity underestimation in the shadow of the tower can be\nsignificant, this redundant velocity measurement enables the observer to select data from\nthe upwind sensor at all times. Even with a boom length nearly 1 1/2 times the tower width,\nthe wind direction readings from the two sensors show the effect of flow distortion caused\nby the tower. The effect is most pronounced for wind directions normal to the booms. Wind\ndirection readings from the opposite ends of the two booms appear to diverge roughly 5° in\neither direction for winds from the ENE and roughly 212° for winds from the WSW. This\ndifference can be attributed to the different aspects of the tower presented to the wind in\neach case; the flat WSW face in the latter case and the apex across from it in the former\ncase.\nTo ensure that the anemometers compared on the tower are embedded in essentially\nthe same flow field the Vaisala and Kaijo Denki anemometers were mounted directly behind\nthe BAO sonic anemometors on the SSE boom (see Figs. 24.4 and 24.5). Vaisala cup and vane\nsensors were installed at the 22-, 100-, 200-, and 300-m levels, and the Kaijo Denki sonic\nanemometer-thermometer occupied the 50-m level. When the results were compared, only\nmeasurements from periods with wind directions between 64° and 244° azimuth were considered.\nThe effect of the direction error on the intercomparison is discussed in the next chapter.\nThe Vaisala temperature sensors were mounted on the NNW booms at all eight\nlevels of the tower. BAO temperature measurements were made from the opposite side, but\nthe flow distortion from the tower did not seem to affect the temperature comparison. The\nVaisala humidity sensors were housed on every other level in the same shields as their\ntemperature sensor; thus they were close to the BAO dew point sensors.\nEffect of Separation Between Sensors\n24.5.2\nA large spatial separation is sometimes unavoidable when sounding systems such as\nsodars are compared with tower sensors. Temporal averaging reduces the variability caused\nby separation, but no guidelines exist on how long the averaging period should be. Here we\n145","No flights of SAM-B or tethered balloons were made during Period 3 because of the need for visual contact with aircraft and balloons.\n1140\n1740\n2340\n$\n1120\n1720\n2320\n1100\n1700\n2300\n1040\n1640\n2240\nindicates carriage measurements.\n1020\n1620\n2220\nTable 24.2. Daily operating schedule for BLIE*\n§\n§\n§\n§\n1000\n1600\n2200\nStarting Time (MDT)\n*This basic schedule was modified when participants dropped out after the first week.\n0940\n1540\n2140\n0920\n1520\n2120\n§\n0900\n1500\n2100\nindicates initial measurement period that was later changed ;\n0840\n1440\n2040\n0820\n1420\n2020\n0800\n1400\n2000\nPeriod 1\n2\n3\n20 Tethersonde+\n2 Kaijo Denki\n13 Echosonde\nSensitron\n16 GMD-1/VIZ\n19 Airsonde\n3 Vaisala\n23 BP/NCART\n4 SAM-B\nXONDAR\nNo. Type\n7 RACES\n8 FM-CW\nIMWM+\n22 NIPR+\n6 TALA\n12 AVIT\n17 TDFS\n18 CORA\nSensor\n1 BAO\n11 WPL\n14\n15\n21","Figure 24.5. Vaisala cup and vane system at the 22-m level.\nexamine the effect of separation to determine if the 20-min averaging specified for BLIE is\neffective in reducing this variability.\nTerrain irregularities of length scales comparable to separation distances\nbetween sensors can introduce systematic differences between their measurements. These\ndifferences cannot be removed by time averaging. The terrain around the BAO site rolls\ngently down toward the west and north but is relatively smooth. Thus the effect of the\nslope should be very small.\nObviously the sampling volumes of the different systems are not at the same\ndistance from the tower. The bistatic systems have their sampling volumes oriented verti-\ncally over the central transmitter (or receiver), but the tilted beams of the monostatic\nsystems point away from the tower toward the west and north, so their separation from the\ntower increases as a function of height.\n147","1.4\nTime\n1.2\nu\n0\nT\nT\nAt\nu,\n1.0\nu +st\nO\n0.8\nUnstable, 1 < U m/s\nUnstable, 5 <<15 m/s\nNear neutral, 1 << 15 m/s\n0.6\n0.4\nNote: Points include data\nfrom 10- and 300-m\nlevels.\n0.2\n0\n0\n1\n2\n3\n4\n5\n6\n7\n8\n9\n10\n11\n12\nT/At (= Tü/d)\nFigure 24. 6. Simulated two-point variance for a downstream\nseparation of sensors plotted as a function of averaging\ntime. Plotted here are variance ratios for T = 1/6, 1/2,\n1, 2, 6, and 10 min with At fixed at 1 min.\nThe effect of averaging can be demonstrated for the simple case where the two\nsensors are aligned along the direction of the mean wind. If the flow is assumed to be\nhorizontally homogeneous and the distance between the sensors small enough that the wind\nfield can be considered frozen, the spatial separation converts to a time lag At = d/,\nwhere d is the distance and u is the mean wind. For typical d = 300 m and II = 5 m/s, the\nlag corresponds to 1 min. In a truly frozen field, 19 of the 20 min would be the same in\nboth measurements, bringing the two averages very close together.\nThe above assumption is tested in Fig. 24.6 with single-point time series of the\nstream-wise wind component, u, measured at two levels on the BAO tower. The variance of\nthe difference across a fixed time lag, normalized by o2 (u), the variance of the time\nseries, is plotted as a function of T/At where T is the averaging time and At is the time\nlag between the two points. For T<<At, the difference variance approaches 202 (u), the\nlimiting value for no correlation between the measurements, but becomes negligible as T\nexceeds 2t. The 20-min averaging should therefore be adequate down to a mean wind speed\nof 2 m/s.\n148","In practice the wind could be blowing from any direction with respect to the line\njoining the two sensors. The frozen-field assumption is no longer applicable, and the\nvariance of the two-point difference increases as the two signals become increasingly\nuncorrelated. The most rapid drop in correlation with distance occurs in the lateral\ndirection. Here one can resort to turbulent time scale arguments to determine the minimum\nrequired averaging time for comparison. Under daytime convective conditions, the loga-\nrithmic spectral peak for horizontal winds typically falls between 0.002 and 0.005 Hz,\nwhich corresponds to a wave period between 3.3 and 8.3 min. Our 20-min averaging period\nshould therefore be adequate even for comparisons between two laterally spaced measurements\nprovided, of course, that the flow is horizontally homogeneous.\nSince sensor separation has a large effect on the sodar/tower sensor comparison, the\nconfiguration of the sodar systems is summarized in Table 24.3 for quick reference.\nTable 24.3. Doppler sodar configurations\nTransmit frequency\nConfiguration\nDetails\nSensor\n(kHz)\nCentral pencil-beam receiver,\nWPL\n1.25\nTwo-axis,\nbistatic\ntwo fan-beam transmitters\nPencil-beam transmit-receivers:\nAVIT\n2.0\nThree-axis,\none pointing vertical, one\nmonostatic\ntilted west, one tilted south\nCentral pencil-beam receiver,\nEchosonde\n2.0\nThree-axis,\nbistatic\ntwo fan-beam transmitters\nPencil-beam transmit-receivers:\nSensitron\n2.4\nTwo-axis,\none tilted west, one tilted\nmonostatic\nnorth\nCentral pencil-beam transmitter-\nThree-axis,\nXONDAR\n2.0\nreceiver, two fan-beam\nbistatic\nreceivers\n24.5.3\nSampling the Same Air Space\nThe problems encountered in the radiosonde intercomparisons differed from those\nin the sodar intercomparisons. The tower measurements have limited value as a common\nreference because of the short time required for the radiosondes to cover the first 300 m.\nRadiosondes launched a few seconds apart sample different air, and even when released in\nclusters are likely to ascend at different rates. Thus a useful comparison of radiosondes\ncan be achieved only by flying the four sondes on a single balloon train.\nThe resolution of the radio frequency crosstalk problem was a matter of criti-\ncal importance. The Vaisala, TDFS, and AIR sondes (see Table 24.1) operated in the 403-MHz\nband, whereas the VIZ sonde used with the GMD-1 operated at 1,680 MHz. Fortunately, some\nof the sondes were tunable to more than one frequency in the 403-MHz band. By adjusting\nthe frequencies (see Table 24.4 for details) and assigning different time periods for the\nradiosonde and tethered balloons (which also shared the 403-MHz band), it was possible to\neliminate crosstalk between the different systems. A trial run before the main inter-\ncomparison demonstrated that the radiosondes could be released simultaneously.\n149","Table 24.4. Telemetering frequencies for radiosondes and tethered balloon profilers\nRadiosondes\nTethered profilers\nSensor type\nFrequency (MHz)\nSensor type\nFrequency (MHz)\nGMD-1/VIZ\n1,680\nBP/NCAR\n403\nCORA\nBetween 400 and 403\nNIPR\nIn-flight recording\nTDFS\n404.17 or 404.59\nIMWM\n393 to 407, with\npeak at 400\nAirsonde\n403.5\nTethersonde\n403.5\nTo attach the four sondes to the single balloon, a yoke consisting of string and\ntwo horizontal pieces of dowel suspended 2 m below the balloon was devised. The Vaisala\nsonde, which must be free to lower itself to operate its reel-activated switch, was sus-\npended from the lower dowel along with the TDFS sonde. The AIR sonde was suspended from\nthe midpoint of the upper dowel, halfway between the vertical string risers that connected\nthe two dowels at their ends, and was thus free to rotate and aspirate its dry and wet\nthermistors. The VIZ sonde was suspended above the upper dowel from the point where the\nyoke was tied to the string from the balloon. Several pairs of hands were needed to\nhandle the balloon train at launch (see Fig. 24.7). The technique described above re-\nsulted in 19 successes out of 20 attempted launches\n24.5.4\nOperation of the Tethered Systems\nTo solve the radio crosstalk problem, the Polish profiling system was assigned\nseparate operating time. The NCAR, AIR and NIPR systems continued to operate simul-\na\ntaneously. Although the winches were spaced as far apart as practical, operators had\nto be alert for tangled lines. Since the line and balloon had to be watched constantly at\nall times, tethered balloons could not be flown after dark.\n24.5.5\nComparisons on the Moving Carriage\nDirect comparisons of all immersion sounding systems (free balloon, tethered\nballoon, and aircraft) were carried out with the aid of the moving carriage on the SW face\nof the tower. The carriage operated at a constant speed, ascending at a rate of 0.55 m/s\nand descending at a rate of 0.57 m/s. As a result, the exact time of arrival of the\ncarriage at each of the instrumented levels was known within a second. A cross arm was\nattached to the end of the boom on the carriage to support the instruments being compared\n(see Fig. 24.8).\nFor the radiosondes, the procedure was to obtain simultaneous profiles to a\nheight of 250 m with the same four sondes that would be subsequently taken aloft on the\nsingle balloon train. At the times corresponding to the tower levels, their observed\nvalues would be compared with the values observed by the tower sensors. Special measures\nwere required to adapt the sondes to the slow ascent rate of the carriage. For example,\nsince the Vaisala sonde was not free to lower and operate its switching reel, a small\nmotor was attached to rotate the reel. The TDFS and AIR sondes were designed to operate at\nascent rates almost an order of magnitude faster than the carriage. A special fan was\ntherefore provided for the TDFS sonde. Initially, the AIR sonde was rotated as if in free\nflight by a motor attached to a stiff wire. Because of problems with this approach, small\nmotors were inserted in the dry- and wet-thermistor ducts. These steps proved to be\nsuccessful.\n150","Figure 24 7 Radiosonde operators\npreparing to release balloon train\nwith all sondes in tow.\nInstrumentation packages used with the tethered balloons and the remotely piloted\naircraft were carried aloft on the carriage, one at a time, during the evening or at other\ntimes when they would not interfere with other instruments.\nBaselining Procedures\n24.5.6\nA conventional, white wooden thermometer shelter was installed in the radiosonde\nlaunch area. A single Assman psychrometer manufactured by Casella and a digital barometer\nmanufactured by Negretti and Zambra were used to obtain baseline data. For the car-\nriage intercomparisons, these instruments were transported to the tower base; at other\ntimes they were located in the thermometer shelter. Since the exact instant of a balloon\nlaunch or carriage ascent was not known in advance, baseline readings of pressure, temper-\nature, and humidity were made at about 5-min intervals and the most recent ones used when\nthe ascent or launch was imminent.\nCOLLECTION AND PROCESSING OF DATA\n24.6\nAccording to the terms of the experiment, the participants were required to sub-\nmit their data to the BLIE organizing committee within 24 h of each observation period.\nThe ability of experimenters to provide processed data within that time was an important this\ninnovation. The use of microprocessors and minicomputers in field equipment made\npossible; besides providing immediate feedback it enabled participants and observers to\n151","Figure 24.8. Radiosondes on cross arm attached to moving carriage on the\nBAO tower.\nreach agreement before they left Boulder on how the sensors compared.\nPhotocopying equip-\nment at the site offered the participants access to other data collected during the exper-\niment for their own analysis.\nThe task of entering all data into the processing computer at Boulder was formid-\nable. Although the data acquired by the on-site computer were transmitted by phone lines\nto the processing computer, the data on sheets turned in by the participants had to be\nentered manually. A team of computer operators worked steadily to keep up with 200 data\nsheets turned in every 24 h. As all data were entered, they were separated according to\nsensor and stored on individual flexible disks. Months of painstaking editing and plot-\nting followed. These data are presented in scatter plots and statistical summaries in\nChapter 25.\n152","25. SUMMARY OF RESULTS\nJ. C. Kaimal and J. E. Gaynor\nNOAA/ERL Wave Propagation Laboratory\nBoulder, Colorado, U.S.A.\nH. W. Baynton\nNational Center for Atmospheric Research\nBoulder, Colorado, U.S.A.\nINTRODUCTION\n25.1\nAlthough the BLIE data justify a wide range of analyses, only a brief overview of\nthe results is presented in this report. Our objective is to make available the comparison\nresults in the form of statistical summaries and scatter diagrams. In keeping with WMO\npolicy we make no attempt to rank the sensors by performance.\nTables 25.1 to 25.9 summarize all data submitted by participants. They include\ninformation on sensor mean, rms difference from reference, and correlation between sensor\nand reference. For all measurements below 300 m, BAO tower data are used as the reference.\nFor radiosonde data, which are measured to a height of 3 km, averages of all sonde meas-\nurements are used as well.\nThe scatter diagrams (Fig. 25.1 to 25.24) include all data included in the sta-\ntistical summaries. In several figures we present additional plots at the request of\nparticipants who wished to highlight certain aspects of the data. In some cases exclu-\nsion of certain levels (or time periods) improved agreement between sensor and tower data.\nAccompanying the figures are comments by BLIE participants and notes from the editors of\nthis report that explain factors which influenced comparison results but were not dis-\ncussed in Chapter 24. The circumstances and limitations described therein should be\nconsidered when the figures are interpreted.\nThe reader is alerted to some errors and discrepancies in the BAO tower reference\nwind data.\n(1) The 300-m Propvane direction reading was in error by +7° from the beginning of the\nexperiment until 1300 MDT on 30 August. Since data from the Propvanes were used only\nfor wind directions between 244° and 64° (clockwise), the number of points affected\nconstitutes 0.5% of the total number of points (including all 8 levels).\n(2) The direction readings from the Propvanes and the sonic anemometers differed by\nas much as 10° (for winds from about 64° azimuth) to 5° (for winds from about 244°\nazimuth) for directions normal to the two booms; this is clearly the result of distor-\ntion in the flow field around the tower. For wind directions from about 64° azimuth,\nthe direction difference exceeded 7° for about 1% of the total data points; for direc-\ntions around 244° azimuth the direction difference was smaller, exceeding 4° for about\n2.5% of the data points.\nErrors in the computed wind components U and V, resulting from the direction errors de-\ntailed above, tend to be small, and since the number of readings affected is also small\ncompared with the total sample, the effect on the statistical summaries is negligible. On\nthe plots, the affected points are lost in the general scatter, so no attempt was made to\nflag or delete them.\n153","25.2\nSTATISTICAL SUMMARIES\nThe notations used in this section follow the conventions adopted by the partici-\npants as outlined in Section 24.2. U and V represent wind components from the west and\nthe south, respectively (in m/s), T and T are the dry-bulb and dew point temperature,\nrespectively (in °C), RH is the relative humidity (in %), and Z is the height (in m) com-\nputed from pressure readings. In earlier sections authors may have used different notations\nto represent the same variables.\nTable 25.1. Statistical summary of data from tower sensors\nNo. of\nBAO\nSensor\nCorre-\nrms\nVariable\nSensor\npoints\ndiff.\nmean\nlation\nmean\n*\nU\nKaijo Denki\n105\n0.74\n0.69\n0.37\n0.99\nVaisala\n365\n-0.31\n-0.33\n0.59\n0.99\nV *\nKaijo Denki\n105\n3.17\n2.76\n0.62\n0.99\nVaisala\n365\n2.66\n2.59\n0.49\n0.98\nW *\nKaijo Denki\n168\n0.03\n0.06\n0.09\n0.70\nVaisala\n-\n-\n-\n-\n-\nT\nKaijo Denki\n179\n23.05\n24.08\n1.15\n1.00\nVaisala\n969\n22.64\n22.81\n0.33\n1.00\nT\nKaijo Denki\n-\n-\n-\nd\n-\n-\nVaisala\n963\n4.25\n4.32\n0.77\n0.99\nRH\nKaijo Denki\n-\n-\n-\n-\n-\nVaisala\n572\n32.80\n32.15\n1.89\n1.00\n*\nIncludes only winds between 64° and 244° azimuth.\nTable 25.2. Statistical summary of data from RACES and SAM-B sensors\nNo. of\nBAO\nSensor\nCorre-\nrms\nVariable\nSensor\npoints\ndiff.\nmean\nlation\nmean\nMode*\nT\nRACES+\n52\n21.67\n21.48\n1.40\n0.92\nSAM-B\n88\n22.31\n21.90\n0.72\n0.99\n(air. ascent)\n11\n88\n22.31\n22.13\n0.81\n0.98\n(air. descent)\n11\n14\n25.24\n25.68\n0.90\n0.89\n(car. ascent)\n11\n14\n25.24\n26.29\n1.18\n0.98\n(car. descent)\nT\nSAM-B\n85\n6.30\n5.87\n1.95\n0.89\n(air. ascent)\nd\n11\n85\n6.30\n5.81\n2.02\n0.90\n(air. descent)\n11\n14\n6.04\n7.74\n2.07\n0.99\n(car. ascent)\n\"\n14\n6.04\n8.35\n2.56\n1.00\n(car. descent)\nRH\nSAM-B\n85\n39.45\n38.68\n5.20\n0.96\n(air. ascent)\n\"\n85\n39.45\n38.42\n4.41\n0.97\n(air. descent)\n11\n14\n30.43\n34.29\n5.51\n1.00\n(car. ascent)\n11\n14\n30.43\n34.36\n5.44\n1.00\n(car. descent)\n*\nSonde operated in remotely piloted aircraft (air.) or on carriage (car.).\nt RACES measured only temperature.\n154","Table 25.3. Statistical summary of data from TALA and FM-CW sensors\nCorre-\nNo. of\nBAO\nSensor\nrms\ndiff.\nlation\nVariable\nSensor\npoints\nmean\nmean\n(4.31)t\n0.96\n0.94\nTALA 1*\n0.94\n0.97\n25\nU\n(8.64)\n1.72\n0.92\nTALA 2*\n12\n3.89\n2.94\n3.32\n0.75\n0.36\n-0.17\nFM-CW\n124\n(4.31)\n1.24\n0.82\n0.98\nTALA 1*\n25\n1.12\nV\n(8.64)\n1.15\n0.97\nTALA 2*\n12\n6.51\n5.99\n0.66\n2.66\n-0.34\n-0.90\nFM-CW\n19\n* TALA 1 is the small kite used during light winds. TALA 2 is the large kite used\nduring strong winds.\nt Mean wind speed for comparison periods.\nTable 25.4. Statistical summary of data from sodars\nCorre-\nNo. of\nBAO\nSensor\nrms\ndiff.\nlation\nVariable\nSensor\npoints\nmean\nmean\n0.95\n0.97\n201\n0.71\n1.04\nU\nWPL\n0.04\n0.01\n0.82\n0.97\nAVIT\n308\n0.87\n1.21\n1.57\nEchosonde\n127\n0.99\n0.36\n-0.93\n2.52\n0.80\nSensitron\n111\n-0.06\n0.97\n0.97\nXONDAR\n201\n0.09\n0.64\n0.36\n1.25\n0.92\n201\nV\nWPL\n0.77\n0.85\n0.97\nAVIT\n308\n0.82\n0.68\n2.12\n0.86\n1.52\nEchosonde\n127\n0.88\n1.30\n2.21\n0.71\nSensitron\n102\n1.05\n1.03\n0.96\nXONDAR\n205\n1.04\nW\nWPL\n-\n-\n-\n-\n-\n0.07\n0.34\n0.32\n244\n-0.03\nAVIT\n-0.05\n0.08\n0.28\n0.03\nEchosonde\n83\nSensitron\n-\n-\n-\n-\n0.62\n0.30\nXONDAR\n154\n0.07\n0.18\n155","Table 25.5. Statistical summary of data from balloon-borne\nradiosondes (10-300 m)*\nNo. of\nBAO\nSensor\nCorre-\nrms\nVariable\nSensor\npoints\nmean\ndiff.\nmean\nlation\nT\nGMD-1/VIZ\n234\n23.15\n23.33\n0.86\n0.98\nCORA\n152\n23.81\n23.48\n0.83\n0.98\nTDFS\n138\n23.63\n23.08\n0.80\n0.99\nAirsonde\n160\n23.82\n23.93\n1.09\n0.95\nT d\nGMD-1/VIZ\n188\n5.55\n6.48\n2.06\n0.86\nCORA\n150\n3.57\n3.88\n1.41\n0.97\nTDFS\n136\n3.81\n4.51\n1.85\n0.95\nAirsonde\n158\n3.83\n6.35\n3.41\n0.90\nRH\nGMD-1/VIZ\n188\n36.73\n37.90\n4.99\n0.96\nCORA\n150\n30.14\n31.70\n4.10\n0.98\nTDFS\n136\n31.17\n34.01\n4.89\n0.98\nAirsonde\n160\n31.05\n35.76\n7.03\n0.95\nU\nGMD-1/VIZ\n-\n-\n-\n-\n-\nCORA\n149\n0.26\n0.14\n2.13\n0.77\nTDFS\n-\n-\n-\n-\n-\nAirsonde\n-\n-\n-\n-\n-\nV\nGMD-1/VIZ\n-\n-\n-\n-\n-\nCORA\n149\n0.90\n0.96\n2.04\n0.80\nTDFS\n-\n-\n-\n-\n-\nAirsonde\n-\n-\n-\n-\n-\n* GMD-1/VIZ wind data not computed for this height range. TDFS and Airsonde\ndid not measure wind.\nTable 25.6. Statistical summary of data from balloon-borne radiosondes (10 m - 3 km)*\nNo. of\nMean of\nSensor\nCorre-\nrms\nVariable\nSensor\npoints\nall sondes\ndiff.\nmean\nlation\nT\nGMD-1/VIZ\n255\n17.83\n18.03\n0.58\n1.00\nCORA\n255\n17.83\n17.71\n0.36\n1.00\nTDFS\n255\n17.83\n17.37\n0.58\n1.00\nAirsonde\n255\n17.83\n18.18\n0.71\n1.00\nT\nGMD-1/VIZ\n204\n1.90\n1.38\n1.31\n0.99\nd\nCORA\n204\n1.90\n1.16\n1.16\n0.99\nTDFS\n204\n1.90\n1.67\n1.02\n0.99\nAirsonde\n204\n1.90\n3.37\n1.98\n0.98\nRH\nGMD-1/VIZ\n204\n37.92\n35.96\n3.60\n0.98\nCORA\n204\n37.92\n36.09\n3.39\n0.98\nTDFS\n204\n37.92\n38.97\n3.21\n0.98\nAirsonde\n204\n37.92\n40.68\n4.57\n0.96\nZ\nGMD-1/VIZ\n255\n10.28\n-\n1.00\n(-1.01)\n-\nCORA\n255\n5.28\n-\n1.00\n(1.37)\n-\nTDFS\n255\n6.45\n(2.41) ¥\n-\n1.00\n-\nAirsonde\n255\n11.59\n-\n1.00\n(-2.78)\n-\n* Only periods when all four sondes functioned satisfactorily are included in this\ncomparison. Complete wind data provided only by CORA. GMD-1/VIZ gave wind data\nfor two levels below 3 km.\nt Difference in reported height from mean for all sondes.\n156","Table 25.7.\nStatistical summary of data from radiosondes on\ncarriage (10-300 m)\nNo. of\nBAO\nSensor\nCorre-\nrms\ndiff.\nlation\nVariable\nSensor\npoints\nmean\nmean\n23.44\n23.41\n0.82\n0.97\nT\nGMD-1/VIZ\n126\nCORA\n133\n23.62\n23.86\n0.66\n0.99\nTDFS\n113\n23.89\n23.42\n0.71\n0.99\nAirsonde\n126\n23.60\n24.07\n0.92\n0.98\n5.43\n1.98\n0.90\nT\nGMD-1/VIZ\n40\n5.08\nd\n4.82\nCORA\n131\n5.09\n1.31\n0.97\nTDFS\n112\n4.28\n3.83\n1.34\n0.97\nAirsonde\n124\n4.63\n5.08\n1.08\n0.98\n34.22\n5.15\n0.95\nRH\nGMD-1/VIZ\n40\n34.25\n2.61\n0.99\nCORA\n131\n33.09\n33.42\nTDFS\n112\n31.47\n31.53\n2.28\n0.99\n32.66\n0.99\nAirsonde\n118\n32.61\n2.70\nTable 25.8. Statistical summary of data from tethered balloon sensors\nNo. of\nBAO\nSensor\nCorre-\nrms\ndiff.\nlation\nVariable\nSensor\npoints\nmean\nmean\n0.88\n0.99\nT\nTethersonde\n112\n21.28\n21.17\n1.24\n0.96\nIMWM\n119\n21.49\n21.56\n5.19\n0.31\nNCAR\n59\n25.18\n28.07\n3.09\n0.83\nT\nTethersonde\n106\n6.19\n8.36\nd\nIMWM\n109\n6.09\n7.15\n2.34\n0.82\n11.74\n0.53\nNCAR\n59\n-1.28\n7.17\n46.86\n6.66\n0.97\nRH\nTethersonde\n106\n42.48\n41.67\n44.24\n8.53\n0.89\nIMWM\n109\n19.01\n0.58\nNCAR\n59\n18.07\n29.73\n(5.33) T\nZ*\n17.33\n1.00\nTethersonde\n141\n-\n-\nIMWM\n-\n-\n-\n-\n-\n(4.63)\n22.28\n0.99\nNCAR\n78\n-\n-\n0.86\nS§\nTethersonde\n111\n3.05\n2.85\n0.98\n5.47\n1.92\n0.91\nIMWM\n53\n4.46\n3.56\n1.16\n0.69\nNCAR\n59\n3.25\n* Height above ground determined from pressure.\nt Mean difference with respect to actual height.\n§ Wind speed used for this comparison since IMWM did not measure wind direction.\n157","Table 25.9. Statistical summary of data from tethered balloon sensors\non carriage\nNo. of\nBAO\nSensor\nCorre-\nrms\nVariable\nSensor\npoints\ndiff.\nlation\nmean\nmean\nT\nTethersonde\n14\n20.89\n21.15\n0.35\n0.99\nIMWM\n55\n24.60\n24.31\n0.65\n0.97\nNIPR\n-\n-\n-\n-\n-\nNCAR\n14\n24.70\n24.92\n0.43\n0.97\nT\nTethersonde\n13\n9.73\n10.82\n1.26\n0.99\nd\nIMWM\n51\n5.69\n6.06\n1.36\n0.98\nNIPR\n-\n-\n-\n-\n-\nNCAR\n14\n6.01\n6.79\n1.19\n0.84\nRH\nTethersonde\n13\n50.93\n54.08\n3.94\n0.99\nIMWM\n51\n32.49\n34.48\n3.90\n0.99\nNIPR\n-\n-\n-\n-\n-\nNCAR\n14\n30.47\n31.66\n2.26\n0.92\nZ\nTethersonde\n14\n6.04\n1.00\n(2.23)*\n-\n-\nIMWM\n55\n12.26\n0.99\n(-0.39)*\n-\n-\nNIPR+\n5\n3.85\n1.00\n(-3.20)*\n-\n-\nNCAR\n14\n5.88\n1.00\n(-0.37)*\n-\n-\nSS\nTethersonde\n14\n6.52\n6.15\n0.53\n0.98\nIMWM\n53\n4.46\n5.47\n1.92\n0.91\nNIPR+\n5\n1.63\n2.06\n1.67\n0.64\nNCAR\n-\n-\n-\n-\n-\n* Mean difference from actual heights\nt\nNIPR data were not processed electronically but averaged by eye.\n§\nWind speed used for this comparison since IMWM did not measure wind direction.\n25.3\nSCATTER DIAGRAMS AND NOTES\nIn the following scatter diagrams the scales on the axes convert directly to\nmeteorological units when multiplied by the factor (10, 100, or 1000) indicated in paren-\ntheses. The wind components U and V are given in m/s; temperatures and dew points in °C;\nheights in m; relative humidities in %.\n158","TEMPERATURE\nI-COMPONENT\n3.00\n1.60\n2.50\n0.50\n2.00\n0.00\n1.50\n-0.50\n1.00\n-1.00\n2.50\n3.00\n0.50\n1.00\n1.00\n1.50\n2.00\n0.00\n-1.00\n-0.50\n(x 10)\nBAO\n(x 10)\nBAO\nV-COMPONENT\n1.00\nN\nV\nBLIE Wind\nComponents\n154°\n0.50\nU\n0.00\n94°\n-0.50\nWind directions\nmost affected by\n214°\ntransducer wake\n-1.00\n0.50\n1.00\n0.00\n-1.00\n-0.50\n(x 10)\nBAO\nFigure 25. 1. Scatter plots of data from Kaijo Denki sonic anemometer-\nthermometer at 50-m level vs. data from BAO tower sensors. Sketch shows\norientation of the Kaijo Denki probe on the SSE boom.\nNotes on Fig. 25.1\n1. Only wind directions from 64° to 244° (clockwise) are included in this compari-\nson. Not many data points occur on the negative side of V because of this restriction.\n2. Significant departures from the 1-to-1 lines (for U 112 -5 m/s and V 11 5 m/s) may be\nattributed to (1) absence of correction for transducer blockage of flow along the Kaijo\nDenki axes (see sketch in Fig. 25.1), (2) overcorrection for same effect in the BAO sonic\nanemometer, or (3) distortion of flow field around the tower. The lack of such a clear\ntrend away from the 1-to-1 line in the Vaisala- - BAO plots (see Fig. 25.2) suggests that\nthe absence of correction in the Kaijo Denki data is a major factor.\n3. The sonic temperature setting on the instrument appears to be offset by about +1°C;\notherwise, the Kaijo Denki temperature data seem to track the BAO temperature data quite\nwell. The sonic thermometer measures relative changes in temperature more accurately\nthan the absolute temperature.\n159","Notes on Fig. 25.2\n1. The same restriction on wind direction (see Note 1 on Fig. 25.1) applies here for\nthe U and V comparisons. Large scatter for light winds exists because wind components are\nresolved from 20-min averaged speeds and directions in the Vaisala data. .\n2. Temperature comparisons with and without restricting wind directions show no\nsignificant difference in overall scatter. In the former, wind directions are restricted\nto ranges of 34° to 94° and 214° to 274°. Vaisala and BAO temperatures were measured from\nopposite booms (see Section 24.3).\n3. No direction restrictions were imposed for the humidity comparisons.\n160","TEMPERATURE\nU-COMPONENT\n3.00\n1.00\nRestricted Wind\nDirections\n2.50\n0.50\n2.00\n0.00\n1.50\n-0.50\n1.00\n-1.00\n2.00\n2.50\n3.00\n1.50\n1.00\n0.50\n1.00\n-0.50\n0.00\n-1.00\n(x 10)\nBAO\n(x 10)\nBAO\nTEMPERATURE\nV-COMPONENT\n3.00\n1.00\nAll Wind\nDirections\n2.50\n0.50\n2.00\n0.00\n1.50\n-0.50\n1.00\n-1.00\n2.50\n3.00\n1.50\n2.00\n1.00\n1.00\n0.00\n0.50\n-0.50\n-1.00\n(x 10)\nBAO\n(x 10)\nBAO\nDEW POINT\nRELATIVE HUMIDITY\n2.00\n1.00\n1.50\n0.80\n1.00\n0.60\n0.50\n0.40\n0.00\n0.20\n-0.50\n1.50\n2.00\n0.00\n0.00\n0.50\n1.00\n-0.50\n0.60\n0.80\n1.00\n0.40\n0.20\n0.00\n(x 10)\nBAO\n(x 100)\nBAO\nFigure 25.2. Scatter plots of data from Vaisala tower sensors vs. data from\nBAO tower sensors.\n161","Notes on Fig. 25.3\nComments from D. Martin, EERM\n1. SAM-B temperature readings during flight appear to be lower than tower temperature\nreadings by about 0.4°C for ascents and 0.2°C for descents. Although this may be caused by\ncalibration error, the probability is low.\n2. In a 20-min period when temperatures are rising, instantaneous temperatures ob-\ntained from SAM-B at the beginning of the period will be lower than the mean temperature for\nthat period.\n3. Consideration must be given to possible perturbations of the temperature field\ncaused by the tower or the lack of ventilation in tower sensors.\nEditors' response\nThe temperature sensors on the tower are aspirated and shielded. Periodic comparisons\nbetween measurements on the tower and the NCAR aircraft show agreement at 250-m height to\nwithin +0.1°C. Radiation error in the tower measurements is less that 0.04°C.\nNotes on Fig. 25.4\nComments from D. Martin, EERM\nTemperature readings from SAM-B instrument package on carriage are higher than tower\ntemperatures because of lack of adequate ventilation in our sensors while on the carriage.\nThis difference in behavior proves the good ventilation on the SAM-B aircraft.\n162","TEMPERATURE\nTEMPERATURE\n3.00\n3.00\nAircraft\nAircraft\nDescent\nAscent\n2.50\n2.50\n2.00\n2.00\n1.50\n1.50\n1.00\n2.50\n3.00\n2.00\n1.00\n1.50\n1.00\n3.00\n2.50\n2.00\n1.50\n(x 10)\n1.00\nBAO\n(x 10)\nBAO\nDEW POINT\nDEW POINT\n2.00\n2.00\nAircraft\nAircraft\nDescent\n1.50\nAscent\n1.50\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n1.00\n1.50\n2.00\n-0.50\n-0.50\n0.00\n0.50\n2.00\n0.50\n1.00\n1.50\n0.00\n-0.50\n(x 10)\nBAO\n(x 10)\nBAO\nRELATIVE HUMIDITY\nRELATIVE HUMIDITY\n1.00\n1.00\nAircraft\nAircraft\nDescent\n0.80\nAscent\n0.80\n0.60\n0.60\n0.40\n0.40\n0.20\n0.20\n0.00\n0.80\n1.00\n0.00\n0.40\n0.60\n0.00\n0.20\n1.00\n0.20\n0.40\n0.60\n0.80\n0.00\n(x 100)\nBAO\n(x 100)\nBAO\ndata from\nFigure 25.3. Scatter plot of data from SAM-B air-borne sensors vs.\nBAO tower sensors.\n163","TEMPERATURE\nTEMPERATURE\n3.00\n3.00\nCarriage\nCarriage\nAscent\nDescent\n: 1,\n2.50\n2.50\n2.00\n2.00\n1.50\n1.50\n1.00\n1.00\n1.00\n1.50\n2.00\n2.50\n3.00\n1.00\n1.50\n2.00\n2.50\n3.00\nBAO\n(x 10)\nBAO\n(x 10)\nDEW POINT\nDEW POINT\n2.00\n2.00\nCarriage\nCarriage\nAscent\n1.50\nDescent\n1.50\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n-0.50\n0.00\n0.50\n1.00\n1.50\n2.00\n-0.50\n0.00\n0.50\n1.00\n1.50\n2.00\nBAO\n(x 10)\nBAO\n(x 10)\nRELATIVE HUMIDITY\nRELATIVE HUMIDITY\n1.00\n1.00\nCarriage\nCarriage\nAscent\n0.80\nDescent\n0.80\n0.60\n0.60\nTT\n0.40\n0.40\n0.20\n0.20\n0.00\n0.00\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\nBAO\n(x 100)\nBAO\n(x 100)\nFigure 25.4. Scatter plots of data from SAM-B instrument package on carriage\nvs. data from BAO tower sensors.\n164","U-COMPONENT\nU-COMPONENT\n1.00\n1.00\n0.50\n0.50\nT\n0.00\n0.00\nas ⑉\n..\n1\n2\n-0.50\n-0.50\n-1.00\n-1.00\n0.00\n0.50\n1.00\n-1.00\n-0.50\n0.50\n1.00\n-1.00\n-0.50\n0.00\n(x 10)\nBAO\n(x 10)\nBAO\nV-COMPONENT\nV-COMPONENT\n1.00\n1.00\n0.50\n0.50\n1\n0.00\n0.00\n'\n2\n-\n+\n-0.50\n-0.50\n-1.00\n-1.00\n0.50\n1.00\n1.00\n-1.00\n-0.50\n0.00\n0.00\n0.50\n-1.00\n-0.50\n(x 10)\nBAO\n(x 10)\nBAO\nFigure 25.5. Scatter plots of data from TALA 1 and TALA 2 vs. data from BAO\ntower sensors. Tala 1 is the small kite flown during light winds, and\nTALA 2 the large kite flown during strong winds.\nNotes on Fig. 25.5\nComments from C. . F. Woodhouse, Approach Fish, Inc.\n1. The data points in group 1 should be discounted since they were obtained from an\nuncalibrated lift balloon flown at 800-m altitude. The velocity points shown are only\nempirical estimates.\n2. The data points in group 2 should be discounted because of equipment malfunction\ncaused by an attempt to protect the electrical contacts with wet silicone in a thunderstorm.\n165","U-COMPONENT\nTEMPERATURE\n1.00\n3.00\n0.50\n2.50\n0.00\n2.00\n-0.50\n1.50\n-1.00\n1.00\n-1.00\n-0.50\n0.00\n0.50\n1.00\n1.00\n1.50\n2.00\n2.50\n3.00\nBAO\n(x 10)\nBAO\n(x 10)\nV-COMPONENT\n1.00\n0.50\n0.00\n-0.50\n-1.00\n-1.00\n-0.50\n0.00\n0.50\n1.00\nBAO\n(x 10)\nFigure 25.6. Scatter plots of data from FM-CW Doppler radar and RACES\nvs. data from BAO tower sensors.\nNotes on Fig. 25.6\nMore data were collected with the FM-CW radar pointing west than pointing south, which\naccounts for the disparity in the number of data points along the two components.\n166","U-COMPONENT\nU-COMPONENT\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n-1.00\n-1.00\n0.50\n1.00\n-0.50\n0.00\n1.00\n-1.00\n-1.00\n-0.50\n0.00\n0.50\n(x 10)\n(x 10)\nBAO\nBAO\nV-COMPONENT\nV-COMPONENT\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n-1.00\n-1.00\n0.50\n1.00\n-0.50\n0.00\n0.00\n0.50\n1.00\n-1.00\n-1.00\n-0.50\n(x 10)\n(x 10)\nBAO\nBAO\nFigure 25.7. Scatter plots of data from WPL and AVIT Doppler sodars vs. data\nfrom BAO tower sensors.\nNotes on Fig. 25.7\n1. WPL and AVIT data were possibly affected by crosstalk when the sensors were\noperated concurrently for the first 3 days.\n2. The 50-m WPL wind readings were raised by a factor of 2 to correct for attenuation\ncaused by array geometry.\n3. During high winds WPL Doppler measurements were contaminated by tower noise (see\ndiscussion in Chapter 11)\n4. Vertical velocity correction (see section 12.3) was not applied in the wind\ncomputations of either system. For 20-min averaged U and V, this correction provided no\ndetectable improvement.\n167","U-COMPONENT\nU-COMPONENT\n1.00\n1.00\nAll Levels\n100, 150,\nand 200 m\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n-1.00\n-1.00\n-1.00\n-0.50\n0.00\n0.50\n1.00\n-1.00\n-0.50\n0.00\n0.50\n1.00\nBAO\n(x 10)\nBAO\n(x 10)\nV-COMPONENT\nV-COMPONENT\n1.00\n1.00\nAll Levels\n100, 150,\nand 200 m\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n-1.00\n-1.00\n-1.00\n-0.50\n0.00\n0.50\n1.00\n-1.00\n-0.50\n0.00\n0.50\n1.00\nBAO\n(x 10)\nBAO\n(x 10)\nFigure 25.8. Scatter plots of data from Echosonde Doppler sodar vs. data\nfrom BAO tower sensors. Data from 100, 150, and 200 m show better agree-\nment with BAO tower sensor data than those from levels above and below.\nNotes on Fig. 25.8\nComments from M. McAnnally, Radian Corporation\n1. The low bias in the Echosonde wind data is caused by an improper transmit antenna\npattern resulting from an incorrect horn shape and a phasing mismatch between transducer\ndriver pairs used with each horn. Combination of these two factors resulted in a transmit\nbeam pattern that was much broader in azimuth than anticipated. As a result only the alti-\ntude range from 100 to 230 m received adequate acoustic energy.\n2. New transmitter designs have been incorporated into the system, and subsequent\ntesting has provided excellent agreement with observed conditions.\n168","U-COMPONENT\nU-COMPONENT\n1.00\n1.00\n100 and 150 m\nAll Levels\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n-1.00\n-1.00\n0.50\n1.00\n-1.00\n-0.50\n0.00\n0.50\n1.00\n-1.00\n-0.50\n0.00\n(x 10)\n(x 10)\nBAO\nBAO\nV-COMPONENT\nV-COMPONENT\n1.00\n1.00\n100 and 150 m\nAll Levels\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n-1.00\n-1.00\n0.50\n1.00\n-0.50\n0.00\n0.00\n0.50\n1.00\n-1.00\n-1.00\n-0.50\n(x 10)\n(x 10)\nBAO\nBAO\nFigure 25.9. Scatter plots of data from Sensitron Doppler sodar vs. data\nfrom BAO tower sensors. Data from 100 and 150 m show much better agreement\nthan those from levels above and below.\nNotes on Fig. 25.9\nComments from S. Salomonsson, University of Uppsala\n1. The large scatter in the data results from using borrowed (WPL) antennas which we\ncould not tilt more than 22° from the vertical. The measurements may be influenced by the\nvertical wind component, since correction for that effect was not applied.\n2. Our low pulse power (100 W) resulted in weak echo signals above 150 m, whereas\na ringing in the transducer affected measurements below 100 m. Only measurements at 100\nand 150 m are therefore considered appropriate for comparison with tower data.\n3. Our preliminary system is not optimized for sensing at high altitudes but rather\nto explore the PLL technique in Doppler applications. Agreement with tower at 100 and\n150 m indicates that the PLL circuit works fairly well when the echo signals are strong.\n169","U-COMPONENT\nV-COMPONENT\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\nA\n-1.00\n-1.00\n-1.00\n-0.50\n0.00\n0.50\n1.00\n-1.00\n-0.50\n0.00\n0.50\n1.00\nBAO\n(x 10)\nBAO\n(x 10)\nFigure 25.10. Scatter plots of data from XONDAR Doppler sodar vs. data from\nBAO tower sensors. 50-m level data; data contaminated by severe tower\nnoise.\nNotes on Fig. 25.10\nComments from R. L. Peace, Jr. , Xonics, Inc.\n1. The plot contains data points known to be affected by tower-generated wind noise\nand possible crosstalk from two acoustic sounders not officially participating in BLIE. We\nat Xonics would like the data flagged and identified.\n2. Use of 160-ms-long transmit pulse (rather than the 80-ms-long pulse used in a few\nsoundings) resulted in a strong bias of the 50-m-level data toward zero velocity. This\nproblem was not recognized until late in the first week.\n3. We would like to point out discrepancies of the order of 0.5 to 1 m/s in the wind\nspeed and 10° in wind direction between the BAO sonic anemometer and Propvane when the wind\ndirection was between 20° and 120° and between 180° and 300°.\nEditors' response\nThe unsatisfactory 50-m data and those affected by wind noise are easily identified and\nflagged, but points corresponding to the two periods with possible crosstalk are too close\nto the 1-to-1 line to benefit from flagging. Discrepancies between measurements made from\nopposite sides of a tower are not surprising (see discussions in section 25.1). To\nminimize the effect of flow distortion caused by the tower, only measurements from the\nupwind boom were used in the plots. Also, note that computer summaries of Propvane wind\ncomponents made available to all participants were computed from the 20-min averaged speed\nand direction rather than from the instaneous wind components. Such averaging introduced\ndiscrepancies between the sonic anemometer and Propvane statistics for low wind speeds\n(when turbulence intensity is high). However, the Propvane data used in the comparisons\ndescribed here are true components recomputed from the raw data.\n170","TEMPERATURE\nTEMPERATURE\n3.00\n3.00\n10 m to 3 km\n10 to 300 m\n2\n2.50\n2.50\n2.00\n2.00\n1\n1.50\n1.50\n1.00\n1.00\n1.00\n1.50\n2.00\n2.50\n3.00\n1.00\n1.50\n2.00\n2.50\n3.00\n(x 10)\nSonde Average\n(x 10)\nBAO\nDEW POINT\nDEW POINT\n2.00\n2.00\n10 m to 3 km\n10 to 300 m\n1.50\n1.50\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n-0.50\n0.00\n0.50\n1.00\n1.50\n2.00\n0.50\n1.00\n1.50\n2.00\n-0.50\n0.00\n(x 10)\n(x 10)\nSonde Average\nBAO\nRELATIVE HUMIDITY\nRELATIVE HUMIDITY\n1.00\n1.00\n10 m to 3 km\n10 to 300 m\n0.80\n0.80\n0.60\n0.60\n0.40\n0.40\n0.20\n0.20\nKRA\n0.00\n0.00\n0.40\n0.60\n0.80\n1.00\n1.00\n0.00\n0.20\n0.40\n0.60\n0.80\n0.00\n0.20\n(x 100)\n(x 100)\nSonde Average\nBAO\nFigure 25.11. Scatter plots of balloon-borne - GMD-1/VIZ radiosonde data vs.\nBAO tower data and vs. average for all radiosondes. Data in the righthand\ngroup are restricted to periods when all four sondes were functioning sat-\nisfactorily.\n171","Notes on Fig. 25.11\nComments from R. B. McBeth, NCAR\n1. Points in group 1 are too high because the operator failed to apply the frequency\ndrift correction.\n2. Points in group 2 are 10-m temperatures at about 2315 MDT. The sondes in these\ntwo instances were launched before they had come to thermal equilibrium with the cold\noutside air. Measurements from both sondes agreed within 0.4°C with the tower data during\nthe carriage ascent that preceded the launch.\n172","RELATIVE HUMIDITY\nTEMPERATURE\n1.00\n3.00\nCarriage\nCarriage\n0.80\n2.50\n0.60\n1\n2.00\n0.40\n1.50\n0.20\n0.00\n1.00\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\n1.50\n2.00\n2.50\n3.00\n1.00\n(x 100)\n(x 10)\nBAO\nBAO\nHEIGHTS\nDEW POINT\n3.00\n2.00\nFree Ascent\nCarriage\n10 m to 3 km\n1.50\n2.00\n1.00\n0.50\n1.00\n0.00\n0.00\n-0.50\n0.00\n1.00\n2.00\n3.00\n1.00\n1.50\n2.00\n-0.50\n0.00\n0.50\n(x 1000)\n(x 10)\nSonde Average\nBAO\nFigure 25.12. (Upper, left and right, and lower, left) Scatter plots of data\nfrom GMD-1/VIZ radiosondes on carriage vs. data from BAO tower sensors.\n(Lower, right) GMD-1/VIZ radiosonde computed heights vs. average heights for\nall balloon-borne radiosondes.\nNotes on Fig. 25.12\nComments from R. B. McBeth, NCAR\nThe very low values in group 1 are believed to result from computational error. When\nthe same sonde was flown from the balloon, its measurements averaged 0. 13°C higher than the\naverage data of the other three sondes and 0.19°C lower than those from the tower.\n173","TEMPERATURE\nTEMPERATURE\n3.00\n3.00\n10 to 300 m\n10 m to 3 km\n2.50\n2.50\n2.00\n2.00\n1.50\n1.50\n1.00\n1.00\n1.00\n1.50\n2.00\n2.50\n3.00\n1.00\n1.50\n2.00\n2.50\n3.00\nBAO\n(x 10)\nSonde Average\n(x 10)\nDEW POINT\nDEW POINT\n2.00\n2.00\n10 to 300 m\n10 m to 3 km\n1.50\n1.50\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n-0.50\n0.00\n0.50\n1.00\n1.50\n2.00\n-0.50\n0.00\n0.50\n1.00\n1.50\n2.00\nBAO\n(x 10)\nSonde Average\n(x 10)\nRELATIVE HUMIDITY\nRELATIVE HUMIDITY\n1.00\n1.00\n10 to 300 m\n10 m to 3 km\n0.80\n0.80\n0.60\n0.60\n0.40\n0.40\n0.20\n0.20\n0.00\n0.00\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\nBAO\n(x 100)\nSonde Average\n(x 100)\nFigure 25.13. Scatter plots of balloon-borne TDFS radiosonde data vs. BAO\ntower data and vs. average for all radiosondes. Data in righthand group\nare restricted to periods when all four sondes were functioning satis-\nfactorily.\n174","Notes on Fig. 25.13\nComments from E. Schöllmann, Deutscher Wetterdienst\n1. The TDFS data have no radiation error because the sensors are well aspirated and\nhoused in a radiation shield. The sensors are bead thermistors with fast response.\nDiscrepancies between the sonde and the tower profiles may result because data are\n2.\nnot compared at significant points but at fixed pressure steps.\nRELATIVE HUMIDITY\nTEMPERATURE\n1.00\n3.00\nCarriage\nCarriage\n0.80\n2.50\n0.60\n2.00\n0.40\n1.50\n0.20\n0.00\n1.00\n0.60\n0.80\n1.00\n0.00\n0.20\n0.40\n3.00\n2.50\n2.00\n1.50\n1.00\n(x 100)\nBAO\n(x 10)\nBAO\nHEIGHTS\nDEW POINT\n3.00\n2.00\nFree ascent\nCarriage\n10 m to 3 km\n1.50\n2.00\n1.00\n0.50\n1.00\n0.00\n0.00\n3.00\n-0.50\n1.00\n2.00\n0.00\n1.50\n2.00\n1.00\n0.00\n0.50\n-0.50\n(x 1000)\nSonde Average\n(x 10)\nBAO\nFigure 25.14. (Upper, left and right, and lower, left) Scatter plots of (Lower, data\nfrom TDFS radiosondes on carriage vs. data from BAO tower sensors.\nright) TDFS radiosonde computed heights vs. average heights for all balloon-\nborne radiosondes.\n175","TEMPERATURE\n3.00\nTEMPERATURE\n3.00\n101\n10 to 300 m\n10 m to 3 km\n2.50\n2.50\n2.00\n2.00\n1.50\n1.50\n1.00\n1.00\n1.00\n1.50\n2.00\n2.50\n3.00\n1.00\n1.50\n2.00\n2.50\n3.00\nBAO\n(x 10)\nSonde Average\n(x 10)\nDEW POINT\n2.00\nDEW POINT\n2.00\n10 to 300 m\n10 m to 3 km\n1.50\n1.50\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n-0.50\n0.00\n0.50\n1.00\n1.50\n2.00\n-0.50\n0.00\n0.50\n1.00\n1.50\n2.00\nBAO\n(x 10)\nSonde Average\n(x 10)\nRELATIVE HUMIDITY\n1.00\nRELATIVE HUMIDITY\n1.00\n10 to 300 m\n10 m to 3 km\n0.80\n0.80\n0.60\n0.60\n0.40\n0.40\n0.20\n0.20\n0.00\n0.00\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\nBAO\n(x 100)\nSonde Average\n(x 100)\nFigure 25.15. Scatter plots of balloon-borne CORA radiosonde data vs. data\nfrom BAO tower data and vs. average for all radiosondes. Data in the\nrighthand group are restricted to periods when all four sondes were func-\ntioning satisfactorily.\n176","Notes on Fig. 25.15\nThe CORA system measured relative humidity with a Humicap sensor that has a faster\nresponse than the wet-bulb systems used in the TDFS and Airsonde.\nRELATIVE HUMIDITY\nTEMPERATURE\n1.00\n3.00\nCarriage\nCarriage\n0.80\n2.50\n0.60\n2.00\n0.40\n1.50\n0.20\n0.00\n1.00\n1.00\n0.00\n0.20\n0.40\n0.60\n0.80\n3.00\n2.00\n2.50\n1.50\n1.00\n(x 100)\nBAO\n(x 10)\nBAO\nHEIGHTS\nDEW POINT\n3.00\n2.00\nFree Ascent\nCarriage\n10 m to 3 km\n1.50\n2.00\n1.00\n0.50\n1.00\n0.00\n0.00\n3.00\n-0.50\n1.00\n2.00\n0.00\n1.00\n1.50\n2.00\n0.50\n0.00\n-0.50\n(x 1000)\nSonde Average\n(x 10)\nBAO\nFigure 25.16. (Upper, left and right, and lower, left) Scatter plots of data\nfrom CORA radiosondes on carriage vs. data from BAO tower sensors. (Lower,\nright) CORA radiosonde computed heights vs. average heights for all balloon-\nborne radiosondes.\n177","TEMPERATURE\nTEMPERATURE\n3.00\n3.00\n10 to 300 m\n10 m to 3 km\n2.50\n2.50\n2.00\n2.00\n1.50\n1.50\n1.00\n1.00\n1.00\n1.50\n2.00\n2.50\n3.00\n1.00\n1.50\n2.00\n2.50\n3.00\nBAO\n(x 10)\nSonde Average\n(x 10)\nDEW POINT\nDEW POINT\n2.00\n2.00\n10 to 300 m\n10 m to 3 km\n1.50\n1.50\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n-0.50\n0.00\n0.50\n1.00\n1.50\n2.00\n-0.50\n0.00\n0.50\n1.00\n1.50\n2.00\nBAO\n(x 10)\nSonde Average\n(x 10)\nRELATIVE HUMIDITY\nRELATIVE HUMIDITY\n1.00\n1.00\n10 to 300 m\n10 m to 3 km\n0.80\n0.80\n0.60\n0.60\n0.40\n0.40\n0.20\n0.20\n0.00\n0.00\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\nBAO\n(x 100)\nSonde Average\n(x 100)\nFigure 25.17. Scatter plots of balloon-borne Airsonde data vs. BAO tower\ndata and vs. average for all radiosondes. Data in the righthand group are\nrestricted to periods when all four sondes were functioning satisfactorily.\n178","RELATIVE HUMIDITY\nTEMPERATURE\n1.00\n3.00\nCarriage\nCarriage\n0.80\n2.50\n0.60\n2.00\n0.40\n1.50\n0.20\n0.00\n1.00\n1.00\n0.20\n0.40\n0.60\n0.80\n0.00\n3.00\n2.50\n2.00\n1.50\n1.00\n(x 100)\nBAO\n(x 10)\nBAO\nHEIGHTS\nDEW POINT\n3.00\n2.00\nFree Ascent\nCarriage\n10 m to 3 km\n1.50\n2.00\n1.00\n0.50\n1.00\n0.00\n0.00\n-0.50\n2.00\n3.00\n0.00\n1.00\n1.50\n2.00\n1.00\n0.00\n0.50\n-0.50\n(x 1000)\nSonde Average\n(x 10)\nBAO\nFigure 25.18. (Upper, left and right, and lower, left) Scatter plots of\ndata from Airsondes on carriage vs. data from BAO tower sensors. (Lower,\nright) Airsondes computed heights vs. average heights for all balloon-borne\nradiosondes.\nNotes on Figs. 25.17 and 25.18\nComments from D. B. Call, AIR, Inc.\n1. At first, Airsonde temperatures and dew points were often 2°C or 3°C too high in\nfull sunlight but generally accurate at dusk and after sunset. The problem, identified as\nradiative heating, was corrected by painting the thermistor beads white and the insides of\nthe two ducts black (reverse of original colors) Data from modified Airsondes for 4 and\n5 September show excellent agreement with tower data (see Fig. 25.19).\n2. The consistent positive bias of the dew points (Fig. 25.17) is caused by absence\nof any aspiration of the wet thermistor until the instant of launch when the Airsonde began\nto rotate. The error rapidly diminishes during the first minute of flight and could be\neliminated by forced aspiration of the wet thermistor while the Airsonde is on the ground.\nIn the carriage ascents (Fig 25. 18) the thermistors were aspirated before data collection,\nwhich brought the dew point readings to equilibrium.\n179","Notes on Fig. 25.19\nComments from D. B. Call, AIR, Inc.\n1. Results are restricted to data obtained with Airsondes modified to reduce radiative\nheating.\n2. On these two days, for the carriage ascents, the wet-bulb thermistor was aspirated\nby a small electric fan throughout the ascent, beginning a few minutes before ascent.\nThus the wet-bulb temperatures are properly depressed, and the dew point data are in good\nagreement with those of the tower.\n3. For balloon ascents, there is little aspiration of the wet thermistor until the\nAirsonde begins to rotate. Since the wet thermistor requires a minute or two to cool to\nits proper value, the first few indicated dew points (and relative humidity) are higher\nthan those of the tower.\n180","TEMPERATURE\nTEMPERATURE\n3.00\n3.00\nCarriage\nFree Ascent\n4,5 Sept\n4,5 Sept\n2.50\n2.50\n2.00\n2.00\n1.50\n1.50\n1.00\n1.00\n2.00\n2.50\n3.00\n1.00\n1.50\n2.00\n2.50\n3.00\n1.00\n1.50\n(x 10)\nBAO\n(x 10)\nBAO\nDEW POINT\nDEW POINT\n2.00\n2.00\nCarriage\nFree Ascent\n4,5 Sept\n4,5 Sept\n1.50\n1.50\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n1.00\n1.50\n2.00\n0.50\n2.00\n-0.50\n0.00\n0.00\n0.50\n1.00\n1.50\n-0.50\n(x 10)\nBAO\n(x 10)\nBAO\nRELATIVE HUMIDITY\nRELATIVE HUMIDITY\n1.00\n1.00\nCarriage\nFree Ascent\n4,5 Sept\n0.80\n4,5 Sept\n0.80\n0.60\n0.60\n0.40\n0.40\n0.20\n0.20\n0.00\n0.00\n0.60\n0.80\n1.00\n0.20\n0.40\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\n0.00\n(x 100)\nBAO\n(x 100)\nBAO\nFigure 25.19. Scatter plots of data from Airsondes vs. data from BAO tower\nsensors for 4 and 5 September 1979.\n181","Notes on Fig. 25.20\nComments from A. L. Morris, Ambient Analysis\n1. The three plots on the left (tethered balloon ascents) show a positive bias that is\nabsent in the plots on the right (carriage ascents). Since the balloon ascents were made at\nmidmorning and midafternoon whereas the carriage ascents were in the evening, solar radia-\ntion undoubtedly contributed to the bias.\n2. After the intercomparison experiment, the inside of the aspirated duct was painted\nblack to reduce radiation errors.\n182","TEMPERATURE\nTEMPERATURE\n3.00\n3.00\nCarriage\nTethered\n2.50\n2.50\n2.00\n2.00\n1.50\n1.50\n1.00\n1.00\n3.00\n2.00\n2.50\n1.50\n1.00\n1.50\n2.00\n2.50\n3.00\n1.00\n(x 10)\nBAO\n(x 10)\nBAO\nDEW POINT\nDEW POINT\n2.00\n2.00\nCarriage\nTethered\n1.50\n1.50\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n2.00\n0.50\n1.00\n1.50\n-0.50\n0.00\n2.00\n0.50\n1.00\n1.50\n-0.50\n0.00\n(x 10)\nBAO\n(x 10)\nBAO\nRELATIVE HUMIDITY\nRELATIVE HUMIDITY\n1.00\n1.00\nCarriage\nTethered\n0.80\n0.80\n0.60\n0.60\n0.40\n0.40\n0.20\n0.20\n0.00\n0.00\n0.40\n0.60\n0.80\n1.00\n0.00\n0.20\n1.00\n0.60\n0.80\n0.00\n0.20\n0.40\n(x 100)\nBAO\n(x 100)\nBAO\nFigure 25.20. Scatter plots of data from Tethersonde vs. data from BAO tower\nsensors.\n183","TEMPERATURE\nTEMPERATURE\n3.00\n3.00\nTethered\nCarriage\n2.50\n2.50\n2.00\n2.00\n1.50\n1.50\n1.00\n1.00\n1.00\n1.50\n2.00\n2.50\n3.00\n1.00\n1.50\n2.00\n2.50\n3.00\nBAO\n(x 10)\nBAO\n(x 10)\nDEW POINT\nDEW POINT\n2.00\n2.00\nTethered\nCarriage\n1.50\n1.50\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n3,\n-0.50\n-0.50\n-0.50\n0.00\n0.50\n1.00\n1.50\n2.00\n-0.50\n0.00\n0.50\n1.00\n1.50\n2.00\nBAO\n(x 10)\nBAO\n(x 10)\nRELATIVE HUMIDITY\n1.00\nRELATIVE HUMIDITY\n1.00\nTethered\nCarriage\n0.80\n0.80\n0.60\n0.60\n0.40\n0.40\n5's\nr/\nLittle\n0.20\n0.20\n0.00\n0.00\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\n0.00\n0.20\n0.40\n0.60\n0.80\n1.00\nBAO\n(x 100)\nBAO\n(x 100)\nFigure 25.21. Scatter plots of data from IMWM tethered profiler vs. . data\nfrom BAO tower sensors.\n184","TEMPERATURE\nTEMPERATURE\n3.00\n3.00\nCarriage\nTethered\n2.50\n2.50\n2.00\n2.00\n1.50\n1.50\n1.00\n1.00\n2.00\n2.50\n3.00\n1.00\n1.50\n2.50\n3.00\n2.00\n1.00\n1.50\n(x 10)\n(x 10)\nBAO\nBAO\nDEW POINT\nDEW POINT\n2.00\n2.00\nCarriage\nTethered\nx\n1.50\n1.50\n1.00\n1.00\n0.50\n0.50\n0.00\n0.00\n-0.50\n-0.50\n1.00\n1.50\n2.00\n0.00\n0.50\n2.00\n-0.50\n1.00\n1.50\n0.00\n0.50\n-0.50\n(x 10)\n(x 10)\nBAO\nBAO\nRELATIVE HUMIDITY\nRELATIVE HUMIDITY\n1.00\n1.00\nCarriage\nTethered\n0.80\n0.80\n0.60\n0.60\n0.40\n0.40\n0.20\n0.20\n0.00\n0.00\n0.60\n0.80\n1.00\n0.20\n0.40\n0.80\n1.00\n0.00\n0.40\n0.60\n0.20\n0.00\n(x 100)\nBAO\n(x 100)\nBAO\nFigure 25.22. Scatter plots of data from BP/NCAR sensors vs. data from BAO\ntower sensors.\n185","Notes on Fig. 25.22\nComments from R. B. McBeth, NCAR\nImproper adjustment of the wet-bulb range contributed to the very large dew point\nscatter. At times the range was not adjusted downward promptly to accommodate sudden\ndrops in humidity. The wet bulb was then reported equal to the lower range limit rather\nthan the correct colder value and the computed dew point read much too high. This does\nnot account for all the scatter; the transfer of water to the wet thermistor was probably\ninadequate.\n186","HORIZONTAL WIND\nHORIZONTAL WIND\n1.00\n1.20\nCarriage\nTethered\n1.00\n0.80\n0.80\n0.60\n0.60\n0.40\n0.40\n0.20\n0.20\n0.00\n0.00\n0.60\n0.80\n1.00\n0.00\n0.20\n0.40\n1.00\n1.20\n0.00\n0.20\n0.40\n0.60\n0.80\n(x 10)\nBAO\n(x 10)\nBAO\nHORIZONTAL WIND\nHORIZONTAL WIND\n1.00\n1.20\nCarriage\nTethered\n1.00\n0.80\n0.80\n0.60\n0.60\n0.40\n0.40\n0.20\n0.20\n0.00\n1.00\n0.00\n0.40\n0.60\n0.80\n0.00\n0.20\n1.00\n1.20\n0.80\n0.00\n0.20\n0.40\n0.60\n(x 10)\nBAO\n(x 10)\nBAO\nHORIZONTAL WIND\n1.20\nTethered\n1.00\n0.80\n0.60\n0.40\n0.20\n0.00\n1.00\n1.20\n0.60\n0.80\n0.00\n0.20\n0.40\n(x 10)\nBAO\nFigure 25.23. Scatter plots of horizontal wind speeds from tethered balloon\nsensors (balloon-borne and on carriage) vs. data from BAO tower sensors.\n187","HEIGHTS\n3.00\nHEIGHTS\n3.00\nCarriage\nCarriage\n2.00\n2.00\n1.00\n1.00\n0.00\n0.00\n0.00\n1.00\n2.00\n3.00\n0.00\n1.00\n2.00\n3.00\nBAO\n(x 100)\nBAO\n(x 100)\nHEIGHTS\n3.00\nCarriage\n2.00\n1.00\n0.00\n0.00\n1.00\n2.00\n3.00\nBAO\n(x 100)\nFigure 25.24. Scatter plots of heights from tethered balloon systems vs. BAO\ninstrumentation heights.\n188","CONCLUDING REMARKS\n25.4\nThe results of the BLIE presented in this chapter show generally good agreement\nbetween the tested sensors and BAO sensors. The amount of agreement differs for each\nsensor, but differences are usually small. Where strong disagreement was found, the\nparticipant provided reasonable explanations for departures and outlined correction pro-\ncedures. In one instance a participant modified his sensor midway through the experiment\nand got better agreement for the remaining runs (see Fig. 25.19).\nThe objective of this report is to present BLIE data without interpretation. In\nevaluating the sensors, the reader is urged to give due weight to the comments and notes\naccompanying the figures. Hardware and software changes made by a manufacturer after the\nexperiment also need to be considered, since they may have solved problems experienced\nduring BLIE.\nThe success of any experiment involving many different instruments depends on\nthe cooperation between participants and experiment organizers. The authors note with\ngratitude the grace and generosity with which that cooperation was extended, especially\nin the preparation of this last chapter of the report.\n189\n* U.S. Government Printing Office: 1980-O-677-138/6","A\nDD"]}