Satellite observations are particularly important for monitoring the global changes of atmospheric and surface features. For many parameters, satellite measurements are the only means of obtaining this information, particularly over the oceans and sparsely-populated land areas. For example, multi-spectral measurements from both geostationary and polar-orbiting satellites are key components of the Global Precipitation Climatology Project (GPCP) [Huffman et al., 1996], which has measured global rainfall for over 20 years. In addition, the longstanding National Oceanic and Atmospheric Administration (NOAA)-based Northern Hemispheric snow cover climatology has relied almost solely on satellite observations that are interpreted by satellite analysts [Robinson et al., 1993].