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A Comparison of Soundings Retrieved from Polar Orbiter Radiances by Two Very Different Retrieval Algorithms
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    National Meteorological Center (U.S.)
  • Series:
    Office note (National Centers for Environmental Prediction (U.S.)) ; 287
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  • Description:
    "This paper compares two sets of atmospheric vertical temperature profiles produced from NOAA-7 radiance measurements using two different methods. The first retrieval technique (here after referred to as R1) uses eigenvectors of covariance matrices of radiance, temperature, and water vapor mixing ratio to estimate cloud-free infrared sounding 'radiances and vertical temperature profiles from infrared and microwave spectrometer observations (Smith and Woolf, 1976). This technique is currently used by NESDIS to produce a global set of atmospheric temperature profiles twice daily on an operational basis. The other retrieval technique (henceforth called R2) employs an iterative inverse solution of the radiative transfer equation. This technique requires an initial estimate of the temperature and moisture profiles, usually obtained from an NMC forecast (Smith, 1970; Smith and Woolf, 1981). One potential advantage of this latter method, is that the individual soundings chosen for processing may be selected by a human being through the use of a McIDAS terminal. An operator of such a terminal can carefully edit the infrared and microwave data to be processed by viewing the data on a television console. The operator can also cause geographically proximate soundings of his choice to be spatially averaged before they are processed into temperature profiles. It should be noted that, while a considerable amount of man-machine interaction was used in order to produce the edited sounding sets reported on here, CIMSS has, in the past year, substantially automated the entire editing process. Such a spatially averaged sounding, called a sounding field of view, or SFOV, should be free of unrepresentative radiance information caused by soundings through low clouds, or over snow cover, or unusual terrain, etc. since the operator can exclude these from the average (Smith, et al., 1978). Of course, such spatial averaging reduces the horizontal resolution of the data. The set of soundings described in this paper, on the other hand, was edited not by averaging, but by allowing many more soundings to be included over the same geographical area than are permitted in the operationally processed data with method R1 (Figure 1). Might this greater density of polar orbiter data be an improvement over the current data density, especially over the oceans? This study was undertaken to at least begin to address this question"--Introduction.

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