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.

Raw data are processed as soon as received from NOAA.

Then, the sea surface temperature map is calculated 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.