Satellite Sea Surface Temperature Determination from Microwave and Infrared Radiometry

Abstract

Starting in 1978, the present generation of satellite-borne microwave and infrared radiometers are beginning to demonstrate sea surface temperature (SST) estimation accuracies of 0.5–1.0 C, sufficient to map on a global scale the large-scale SST field and its anomaly with respect to climatological norm. In addition, these sensors provide data on the wind at the sea surface, vertically integrated water vapor and liquid water, rain rate, and atmospheric aerosols, all of which are quite important for climate research. In some cases and for certain satellite instruments, evidence is accumulating which suggests that the 0.5°C rms disagreement between ship or buoy data, and that derived from satellite, may actually be an upper bound on satellite accuracy. This is a result of imperfect space-time co-location, as well as true differences between the ‘skin’ temperature measured by radiometry, and the bulk thermometric temperature usually obtained from ships and buoys. Thus the possibility begins to emerge for determining from space the skin temperature relative to bulk thermometric temperature, at points where the latter is determined, for example, from simple drifting buoys. If this difference can be determined to a few tenths of a degree Celcius, it can be related to the heat and momentum fluxes across the air-sea interface. Since momentum flux can be separately determined by active and passive microwave techniques, it may thus prove possible to determine heat flux (long-wave radiative, plus latent and sensible components) to useful accuracy. This, combined with geostationary satellite methods for measuring the short wave radiation reaching the surface, could provide the means for determining the total heat exchange between the ocean and atmosphere, globally and over long periods of time, on a practical, cost-effective basis, with significant implications for climate studies.