The TRMM Microwave Imager (TMI) is a nine-channel passive microwave radiometer which builds on the heritage of the Special Sensor Microwave/Imager (SSM/I) instrument. It is flown aboard the Defense Meteorological Satellite Program (DMSP) platforms.
The TRMM Precipitation Radar (PR), the first of its kind in space, is an electronically scanning radar, operating at 13.8 GHz that measures the 3-D ... rainfall distribution over both land and ocean, and defines the layer depth of the precipitation.
The TRMM 3B31 Monthly 0.5 deg. x 0.5 deg. Combined Rainfall product, contains Rain rate, rain water, snow and graupel at 28 levels for a latitude band from 40 degree N to 40 degree S. It is derived from the TRMM combined algorithm (2B31), which combines data from the TMI and PR to produce the best rain estimate for TRMM.