SSMIS

SSMIS (Special Sensor Microwave Imager/Sounder) is a conical-scanning passive microwave instrument that combines imaging and atmospheric sounding in a single unit, operated by the US Air Force on Defense Meteorological Satellite Program (DMSP) satellites.^[1][2] The instrument carries 24 channels spanning 19.35 GHz to 183.311 GHz, covering surface emission windows at 19.35, 22.235, and 37 GHz, an imaging channel at 91.655 GHz, a water-vapour window at 150 GHz, and water-vapour absorption channels near 183.311 GHz.^[1] Swath width is 1707 km and fields of view vary by channel from approximately 13x14 km to 42x70 km.^[1] Instrument mass is 96 kg and average power consumption is 135 W.^[1]

SSMIS was built by Northrop Grumman and first flew on DMSP-F16, launched in October 2003.^[3] Subsequent units flew on DMSP-F17 (2006), DMSP-F18 (2009), and DMSP-F19 (2014).^[1] DMSP-F17 experienced noise degradation in its temperature-sounding channels from October 2017 onward.^[1] Unlike the cross-track sounders that preceded it on DMSP (SSM/T), SSMIS uses conical scanning to maintain a consistent incidence angle across the swath.^[2]