The SShyT-1 B3 and SSM/I'-2 B4 units were successfully launched on August 2%, 1994 on Defense Meteorological Satellite Program (DMSP) spacecraft F12 from Vandenberg Air Force Base. The S S W -2 instrument is a fivechannel, microwave total-power radiometer. It has three channels near the 183.310-GHz water vapor resonance line (183+1 GHz, 183+3 GHz, 183+7 GHz), and two window channels (91 GHz and 150 GHz). The S S m -1 is a cross-track step scanning seven-channel Dicke microwave radiometer instrument. It operates in the oxygen absorption region at center frequencies of 50.5, 53.2,54.35,54.9,58.4,58.9, and 59.4 GHz. At a nominal orbit at an altitude of 833 km, brightness temperatures from the SSM/T-1 and SSMR-2 instruments are used in the AFGWC's (Air Force Global Weather Center) weather prediction models. The SSME-2 ground processing software provides profiles of relative humidity, and absolute humidity, and water vapor mass at six mandatory pressure levels. The S S W -1 ground processing software (GPS) estimates airtemperature profiles at fiieen pressure levels and the tropopause. The S S W -1 B3 and SSM/T'-2 B4 units are functioning properly as a microwave temperature sounder and a water-vapor profiler, respectively. All system-component temperatures were within acceptable ranges of operation, and exhibited normal orbital variations as expected. The radiometer sensitivities (NEATS) (less than 0.6 Kelvins and 0.4 Kelvins for S S W -2 B4 and SSMD-1 B3, respectively) agree with groundbased measurements, and are below instrument specified values with some margin. The nominal radiometer gains and the resultant dynamic ranges of all channels indicated that the SShyT-1 unit could measure brightness temperatures between the cold path at 2.7 Kelvins and the warm load of 330 Kelvins (i.e., the maxi" expected scene brightness temperature).
DMSP F12 S S W -1 B3 and SSM/T-2 B4brightness temperatures of all seven S S W -1 and five S S m -2 channels strongly correlate with those of the DMSP F l l S S W -1 B2 and SSMD-2 B5 units. As a result, Aerojet concluded that brightness temperatures from DMSP F12 S S W -S S W -2 B5 units have insignificant instrumentdependent bias error. DMSP F12 SSME-1 B3 and S S W -2 B4 brightness temperatures of all channels behave reasonably within physical ranges. For example, the brightness temperatures of the 91.655-GHz channel show a discontinuity at boundaries between two distinct backgrounds (e.g., ocean and land).
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