The special sensor microwave imager (SSMI) is a seven-channel microwave radiometer which has dual polarized channels at 19, 37, and 85 GHz and a vertically polarized channel at 22 GHz. A detailed evaluation of all SSMI channels is made is arriving at the optimum channel selection for the global identification of precipitation and snow cover without the use of any ancillary information. The resulting algorithm takes the form of a decision tree which uses the dual polarized channels at 19 GHz and the vertically polarized channels at 22 and 85 GHz. These four channels enable the identification of precipitation from all other atmospheric and surface features, including snow cover.