The Along Track Scanning Radiometer (ATSR-1) on board ERS-1 consisted of an Infra-Red Radiometer (IRR) and a Microwave Sounder (MWS). The IRR had four channels and was used for measuring sea-surface temperatures (SST) and cloud-top temperatures,The MWS was a two channel passive radiometer.
The IRR was designed and constructed by a consortium, consisting of Rutherford Appleton Laboratory , Oxford University , Mullard Space Science Laboratory , the UK Meteorological Office and CSIRO in Australia. The MWS was built under the responsibility of Centre de Recherche en Physique de l'Environnement (CRPE) and was physically attached to the IRR and its data was merged with that of the IRR prior to transmission to the ground receiving stations. Both are nationally- funded experiments resulting from an ESA Announcement of Opportunity for a scientific add-on package. The ERS-1 mission ended on 10 March 2000.