Editing Special sensor microwave/imager (section)

The '''Special Sensor Microwave/Imager (SSM/I)''' is a seven-channel, four-frequency, linearly polarized passive [[microwave radiometer]] system.<ref name="Hollinger">Hollinger, J.P. 1989: ''DMSP Special Sensor Microwave/Imager Calibration/Validation''. Final Report, Vol. I., Space Sensing Branch, Naval Research Laboratory, Washington D.C.</ref>  It is flown on board the [[United States Air Force]] [[Defense Meteorological Satellite Program]] (DMSP) Block 5D-2 satellites.  The instrument measures surface/atmospheric microwave [[brightness temperature]]s (TBs) at 19.35, 22.235, 37.0 and 85.5&nbsp;GHz.  The four frequencies are sampled in both horizontal and vertical [[Polarization (waves)|polarizations]], except the 22&nbsp;GHz which is sampled in the vertical only.<ref name="NESDIS">{{cite web|title=Special Sensor Microwave/Imager (SSM/I) and Special Sensor Microwave Imager Sounder (SSMIS) Global Gridded Products|url=http://www.ncdc.noaa.gov/oa/rsad/ssmi/gridded/index.php|publisher=National Environmental Satellite, Data, and Information Service (NESDIS), NOAA|accessdate=24 December 2010}}</ref>

The SSM/I has been a very successful instrument, superseding the across-track and Dicke radiometer designs of previous systems. Its combination of constant-angle rotary-scanning and total power radiometer design has become standard for passive microwave imagers, e.g. TRMM Microwave Imager, AMSR.

Its predecessor, the [[Scanning Multichannel Microwave Radiometer]] (SMMR), provided similar information. Its successor, the Special Sensor Microwave Imager / Sounder ([[SSMIS]]), is an enhanced eleven-channel, eight-frequency system.