Calibration of DMSP F-16 Special Sensor Microwave Imager and Sounder

The Special Sensor Microwave Imager/Sounder (SSMIS) aboard the DMSP F-16 satellite measures the Earth's microwave radiation at frequencies ranging from 19 to 183 GHz. This instrument is designed to improve atmospheric sounding capability by uses of both imaging and sounding channels in the conical scanning mode. However, there remain several outstanding issues related to the SSMIS calibration. First, the energy arises from the emission and/or scattering through its main reflector and results in anomalous scene temperatures. It is estimated that the antenna emission can alone produce brightness temperature variability of 1 to 2 K for its temperature sounding channels and 2 to 4 K for water vapor sounding channels. Second, the counts from its calibration targets are contaminated by solar radiation, especially for its warm load. The radiometer output from the warm load displays some anomalies of 20 to 60 counts (sudden jumps) in several major latitudinal zones where brightness temperatures bias by 0.2 to 0.6 K. These contamination zones also change with season. Finally, the calibration count from cold space view is also contaminated, especially at 183 GHz channels.

This study develops a method to detect and eliminate anomalous antenna emission and to correct solar contamination on the SSMIS warm calibration target. The latitudes of solar contamination can be predicted from orbit time whereas the contamination distribution functions are derived through the Fast Fourier Transformation analysis on warm count Overall, these calibration methods have corrected the most of SSMIS anomaly measurements and will be tested in NOAA SSMIS sounding system.