The SSM/I is flown aboard Defense Meteorological Satellite Program (DMSP) satellites F8, F10, F11, F12, and F13. SSM/I instruments are microwave radiometers that sense emitted microwave radiation. The SSM/I is a 7-channel, 4-frequency, orthogonally polarized, passive microwave radiometric system. The instrument measures combined atmosphere and surface radiances at 19. 3, 22. 2, 37. 0, and 85. 5 GHz.