Wikipedia
SSMIS
The Special Sensor Microwave Imager / Sounder (SSMIS) is a 24-channel, 21-frequency, linearly polarized passive microwave radiometer system. The instrument is flown on board the United States Air Force Defense Meteorological Satellite Program (DMSP) F-16, F-17, F-18 and F-19 satellites, which became operational in November 2005, March 2008 March 2016 and May 2016, respectively. It is the successor to the Special Sensor Microwave/Imager (SSM/I).