Estimates of precipitation from the Defense Meteorological Satellite Program (DSMP) Special Sensor Microwave/Imager (SSM/I) have relied on inter-channel comparisons of radiances to infer precipitation from the emitted radiation from water droplets and ice particles (over oceans) and from the backscattering of microwave radiation by ice particles (over both land and oceans). The resulting estimates have tended to be more accurate than those produced using only radiances from the infrared portion of the spectrum; however, the microwave radiances alone do not provide all of the information that is relevant to precipitation estimation.

In this work, the potential impact of additional information from the National Centers for Environmental Prediction (NCEP) Medium Range Forecast (MRF) model on precipitation retrievals is explored. This additional information includes such relevant parameters as subcloud relative humidity (for determining the evaporation of precipitation), freezing level (for determining the relative concentrations of cloud water and cloud ice), and winds (for determining horizontal displacements of precipitation below cloud level). A data set including Stage III radar/raingauge estimates, Tropical Rainfall Measuring Mission (TRMM) radar/raingauge data, atoll raingauge data, and Oklahoma Mesonet data has been used to evaluate both the performance of the operational SSM/I algorithm and the impacts of the MRF parameters.