The estimation of precipitation from space is an important step towards understanding the hydrological cycle on earth, especially over oceanic areas and remote continental areas where surface rainfall networks are not in place or possible. Most studies have used various microwave channels to infer surface precipitation (Kummerow et al. [1991], Adler et al. [1993]). Graves et al. [1993] and Valdes et al. [1990] have evaluated the sampling error due to the intermittent sampling strategy of the spaceborne system and show that sampling errors over land are higher than those over the ocean. A number of studies have compared in-situ aircraft and ground-based radar measurements of precipitation and/or three-dimensional model results with upwelling microwave measurements in order to determine the sensitivity of the microwave retrieval algorithms to details of the microphysical structure of storms (Smith et al. [1992], Vivekanandan et al. [1990], Vivekanandan et al. [1991], Adler et al. [1991a], Adler et al. [1991b], Yeh et al. [1990], and Fulton and Heymsfield [1991]). In general, these studies show that the upwelling microwave radiation from a storm is quite sensitive to microphysical structures such as the fraction of ice versus liquid hydrometeors and their height level in the storm, and the presence of bright bands.
In addition to remote detection of precipitation, studies by Curry et al. [1990] and Curry and Liu [1992] showed that remote detection of supercooled liquid is possible using upwelling microwave radiation over oceans.