SSM/I was first launched on boad the Defense Meteorological Satellite Program (DMSP) F8 satellite in June of 1987. The DMSP series satellites are in sun-synchronous polar orbits at an altitude of approximately 830 km. The instrument is a seven channel linearly polarized passive microwave radiometer operating at frequencies of 19.36, 22.235, 37.0, and 85.5 GHz. Detailed specifications for the spacecraft and instrument are given by Hollinger et al.  and Hollinger [1989, 1991].