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AMSU-A engineering model calibration
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AMSU-A engineering model calibration
  • Description:
    Thermal-vacuum calibration data generated from the Advanced Microwave Sounding Unit-A (AMSU-A) Engineering Model (EM) were analyzed for assessing the instrument's performance and the results were compared to the required specifications. A new calibration algorithm, which represents a scene target-view radiance in terms of radiometric counts was developed and rested with the calibration data. Nonlinear contribution due to an imperfect square-law detector was incorporated into the calibration algorithm via a nonlinearity parameter, [mu], of which values were determined by least-squares fit of a set of data taken at a fixed instrument temperature. The analysis covers the calibration accuracy, nonlinearity, and radiometric temperature sensitivity (NE[delta]T). We found that all specifications are met by the results derived from the thermal-vacuum chamber test data, except that the NE[delta]T values (0.34K and 0.52K) at channels 9 and 15 (57.29 and 89.0 GHz), which exceed the required specification of 0.25K and 0.5K, respectively, for the two channels. The manufacturer found that the large NE[delta]A value at channel 9 was due to un-optimized mixer and its requirement was waived. The NE[delta]T value at channel 15 exceeds the limit by a small margin and probably meets the requirement within measurement uncertainty. For each channel, a warm target fixed bias correction factor, which plays an important role in this analysis, is incorporated into the calibration algorithm. These fixed bias correction factors (supplied by Aerojet) also depend on the instrument temperatures. This analysis of the AMSU-A data provides us with a better understanding of the instrument's functioning. Experience and information gained from this work provide useful insights into the development of computer software for processing the NOAA-K, L, M, data collected from space in the future.
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