Calibration Anomalies and Radiance Assimilation Correction Strategies for the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager Sounder (SSMIS) Steve Swadley 1 , Gene Poe 2 , Nancy Baker 2 , Clay Blankenship 2 , William Campbell 2 , Benjamin Ruston 2 , David Kunkee 3 , Donald Boucher 3 , William Bell 4 METOC Consulting 1 , The Aerospace Corporation 3 , Met Office 4 Marine Meteorology Division of the Naval Research Laboratory 2 , Monterey, CA 93943 USA 1. Introduction The Defense Meteorological Satellite Program (DMSP) launched the first (F-16) in a series of five spacecraft carrying the Special Sensor Microwave Imager Sounder (SSMIS) on October 18, 2003. The SSMIS is a 24 channel conically scanning microwave radiometer, with center frequencies ranging from 19.35 to 183.31 GHz. The SSMIS instrument is the first conical scanning instrument with temperature and moisture sounding channels, and also adds the first operational mesospheric sounding capability. The F-16 orbit is near 850 km in an inclined 98.8º sun-synchronous polar orbit with a local time of ascending node (LTAN) of 20:03. The main reflector ha a diameter of 0.61 m, and rotates at 31.6 rpm. The F-16 travels at 6.5 km sec - 1 that translates to 12.5 km separation between adjacent scans. The SSMIS scanning geometry and channel characteristics are shown in Figure 1 and Table 1, respectively. Figure 1. SSMIS Scan Geometry A comprehensive SSMIS Calibration and Validation (Cal/Val) program was undertaken and discovered unexpected calibration anomalies in the radiometric data [1]. The two principal anomalies detected were, 1) an intermittent solar intrusion to the warm load calibration target; and 2) reflector emission due to solar heating of the reflector surface itself. Other intermittent calibration anomalies detected were random noise spikes mostly near the South Atlantic Anomaly (SAA), and lunar intrusions into the cold space reflector. Table 1. F-16 SSMIS channel characteristics and comparison to current microwave sensors (AMSU-A, AMSU-B, SSM/I and New Mesospheric channels) Ch. No. Center Frequency [GHz] 1 st IF [MHz] 2 nd IF [MHz] Band Width [MHz] Pol Peak [hPa] 1 50.3 0. 0. 400. V 1000 2 52.8 0. 0. 400. V 700 3 53.596 0. 0. 400. V 400 4 54.40 0. 0. 400. V 200 5 55.50 0. 0. 400. V 100 6 57.29 0. 0. 350. LCP 60 7 59.4 0. 0. 250. LCP 30 8 150.0 1250. 0. 1500. H 9 183.31 6600. 0. 1500. H 10 183.31 3000. 0. 1000. H 11 183.31 1000. 0. 400. H 12 19.35 0. 0. 400. H 13 19.35 0. 0. 400. V 14 22.235 0. 0. 500. V 15 37.0 0. 0. 1500. H 16 37.0 0. 0. 1500. V 17 91.655 900. 0. 1500. V 18 91.655 900. 0. 1500. H 19 63.283248 ±285.271 0. 1.5 LCP 0.02 20 60.792668 ±357.892 0. 1.5 LCP 0.05 21 60.792668 ±357.892 ±2. 1.5 LCP 0.7 22 60.792668 ±357.892 ±5.5 3.0 LCP 2 23 60.792668 ±357.892 ±16. 8.0 LCP 7 24 60.792668 ±357.892 ±50. 30.0 LCP 15 Microwave radiances provided by polar orbiting satellite sensors have become an increasingly important component of observing systems for both global and regional data assimilation systems (DAS) for numerical weather prediction (NWP) systems. Assimilation of radiances from instruments such as the Advanced Microwave Sounding Unit (AMSU) have led to significant reduction in short term forecast errors in the southern hemisphere and improvements in the northern hemisphere in global NWP systems. Microwave