Estimation of temperature and humidity profile information from microwave radiances over different surface types

Existing use of passive microwave radiances to improve temperature and humi dity analyses in the troposphere has been largely restricted to ocean appli cations. Recent studies have shown that useful information can be extracted from the Special Sensor Microwave Imager (SSM/I), particularly for cloud l iquid water and precipitation, over many land and ice surfaces. Furthermore , new work has provided improved estimates of emissivity at frequencies wel l above those normally used for land surface applications using satellite. airborne, and groundbased methods. In the light of these new developments, information theory was used to investigate the potential for microwave atmo spheric temperature and humidity sounding over varied land and ice surfaces using the Advanced Microwave Sounding Unit. It was found that significant information is available even at low altitude over land and sea-ice surface s. With extensive land areas poorly served by conventional in situ sounding methods, this result gives considerable promise for the enhanced use of sa tellite sounding data over land. For temperature sounding, the results show that the sensitivity to emissivity depends strongly on the assumptions mad e about cloud cover. For humidity sounding, and temperature sounding in clo udy areas, an accurate model of emissivity and an accurate a priori estimat e of skin temperature are both required to use sounding data effectively.