Estimation of Temperature and Humidity Profile Information from Microwave Radiances over Different Surface Types

Abstract

Existing use of passive microwave radiances to improve temperature and humidity analyses in the troposphere has been largely restricted to ocean applications. Recent studies have shown that useful information can be extracted from the Special Sensor Microwave Imager (SSM/I), particularly for cloud liquid water and precipitation, over many land and ice surfaces. Furthermore, new work has provided improved estimates of emissivity at frequencies well above those normally used for land surface applications using satellite, airborne, and ground-based methods. In the light of these new developments, information theory was used to investigate the potential for microwave atmospheric 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 surfaces. With extensive land areas poorly served by conventional in situ sounding methods, this result gives considerable promise for the enhanced use of satellite sounding data over land. For temperature sounding, the results show that the sensitivity to emissivity depends strongly on the assumptions made about cloud cover. For humidity sounding, and temperature sounding in cloudy areas, an accurate model of emissivity and an accurate a priori estimate of skin temperature are both required to use sounding data effectively.