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The complement of meteorological sensors on-board the DMSP satellite F11, launched in November 1991, included the first passive microwave atmospheric moisture sounder system. This system, designated SSM/T-2, and which includes the ground processing software, retrieves water vapor amounts at the surface and at each of five prescribed mandatory pressure levels to 300 mb in terms of relative humidity and specific humidity, as well as the total column-mass of water vapor and the column-mass of water vapor between mandatory levels to 300 mb, and above 300 mb. Sounding channels include three symmetrically-placed acquisition channels on the 183.310 GHz water vapor absorption line, combined with channels at 150.000 and 91.655 GHz. These channels are used in conjunction with four channels from the SSM/T-1 temperature sounder to produce the humidity values. Prior to 19 June 1993, when a failure of the 150 GHz channel occurred, several calibration/validation studies were performed by USAF, Phillips Laboratory, and Aerospace Corporation. A confirming study was conducted by Aerojet Electronic Systems, builder of the moisture sounding system. Generally, the sounder performance was found to be good, with the exception of a number of cases of anomalously large disagreement with the RAOB ground truth. Investigations of these cases suggests that the cases of anomalously large disagreement between the SSM/T-2 and the verification RAOBs lies in the locally-prevailing complexity of atmospheric structure, e.g., atmospheric baroclinicity, clouds, frontal structures, or simply irregular moisture distribution, and in the differing spatial resolutions of the two types of instruments. Average performance statistics for the moisture sounder are presented along with results of anomaly analysis. Suggestions for improving the verification procedures and for using validation disagreements to improve forecasts are offered.
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