The Special Sensor Microwave Imager/Sounder (SSMIS) radiometer, aboard current and future DMSP satellites, has six Upper Air Sounding (UAS) channels centered at 60.79 and 63.28 GHz. The UAS channels indirectly measure the temperature of the stratosphere and mesosphere between approximately 30 to 80 km altitude (roughly 10 to .01 mb). Assimilation of observations from these channels has the potential to greatly improve NWP forecasts in the stratosphere and mesosphere. Practically, this will facilitate the expansion of NOGAPS-ALPHA (Navy Operational Global Atmospheric Prediction System-Advanced Level Physics, High Altitude).

Effective data assimilation requires an accurate background and an accurate radiative transfer model. Our background consists of a combination of lower-atmospheric profiles from ECMWF analyses and upper-atmospheric LIDAR retrievals taken during the SSMIS Calibration/ Validation Experiment. To accurately model these channels, it is necessary to include polarization-dependent absorption coefficients due to Zeeman splitting. This capability has recently been added to the Community Radiative Transfer Model (CRTM). We test the accuracy of the CRTM for UAS channels by comparing calculated brightness temperatures from CRTM and a Naval Research Laboratory line-by-line model and with SSMIS observations.