The AVHRR radiometer on-board NOAA satellites collects infrared radiation emitted by the sea surface at different wave lengths. AVHRR acquires measurements non-stop along the satellite pass, across a swath of 2,400 kilometers. Complete coverage of the Earth is achieved twice per day. Data are recorded and stored on-board the satellites until they pass over a ground station.

CLS starts processing raw data as soon as they are received from NOAA.

CLS calculates the sea surface temperature by combining AVHRR measurements at different wave lenghts. No sea surface temperature (SST) determination is possible in the presence of clouds. Cloudy areas are thus masked on the maps.