Steps in obtaining sea surface temperature from infra-red imagery

Top panel: quarter of an orbit of Advanced Along Track Scanning Radiometer (AATSR) as a false colour composite of reflectance channels. Channels mapped as follows: Red = ... The orbit passes roughly northward (from left to right) along the North West African coast line, and crosses the northern United Kingdom at around 7000 km: however, it is dusk at this location and the land is not clearly visible. Beyond 8000 km along the track, it is night-time and clouds are no longer visible in the reflectance wavelengths.

Second top panel: same orbit segment at 11 micrometres wavelength. Clouds, being cold, are often obvious as dark features, except where the cloud top height is low. Some clouds are obvious in this infra-red image that are not so clear in the reflectance composite, and vice versa.

Middle panel: calculation of the probability that each pixel represents clear sky. Based on a Bayesian assessment of the radiances compared to simulated radiances (and their covariant uncertainties).

Fourth panel: mask for clear-sky over ocean, based on thresholding the clear-sky probability mask over sea pixels only.

Bottom panel: sea surface temperature derived only for "clear sky" pixels (according to the above mask). The retrieval uses several infra-red channels, at different wavelengths, and in both AATSR views (nadir and oblique).