SST Infra Red and Microwave Sensors

Infra-red radiometers such as the Advanced Very High Resolution Radiometer (AVHRR) on board operational meteorological polar orbiting satellites offer a good horizontal resolution (1 km) and potentially a global coverage, with the important exception of cloudy areas. However, their accuracy (0.4-0.5 K derived from the difference between collocated satellite and buoy measurements) is limited by the radiometric quality of the AVHRR instrument and the correction of atmospheric effects. Geostationary satellites (e.g. GOES and MSG series) are carrying radiometers with similar infrared window channels as the AVHRR instrument. Their horizontal resolution is coarser (3-5 km), but their great contribution comes from their high temporal sampling. Pre-operational demonstrators for advanced measurement of SST suitable for climate studies include the Along Track Scanning Radiometer ((A) ATSR) series of instruments that have improved on board calibration, and make use of dual views at nadir and 55° incidence angle. The along track scanning measurement provides an improved atmospheric correction leading to an accuracy of better than 0.2 K (O'Carroll et al. 2008). The main drawback of these instruments is their limited coverage, due to a much narrower swath than the AVHRR instruments. Several microwave radiometers have also been developed and flown over the last 10 years (e.g. AMSR, TMI). The horizontal resolution of these products is around 25 km and their accuracy around 0.6-0.7 K.

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