Effects of Precipitating and Nonprecipitating Cloud Layers on the Defense Meteorological Satellite Program

摘要

This study is a sensitivity analysis of the Defense Meteorological Satellite Program (DMSP) Block 5D Passive Temperature Sounder (SSM/T) to intervening cloud layers. Brightness temperatures for each of the seven SSM/T channels are calculated based upon two different climatological profiles. Intervening precipitating and nonprecipitating cloud layers are simulated using drop size distributions based upon rainfall rate and Deirmendjian's L-Model cloud, respectively. Radiative transfer through these layers is approximated using the discrete ordinate method for sixteen discrete streams. The effects of such layers on calculated brightness temperatures are shown to vary with cloud position, thickness and precipitation rate. The importance of the variation in the earth's emissivity between land and ocean surfaces is demonstrated. Not only do such variations cause changes in brightness temperature values, but general trends for individual channels are altered. The realative importance of atmospheric, surface emission and cloud effects is broken out for the Mid-Latitude Spring/Fall profile over ocean. The effects of resulting brightness temperature variations on the Air Force Global Weather Central (AFGWC) statistical temperature retrieval technique and Chahine's relaxation technique are also presented.