The ERS satellites carry instrumentation consisting of a core set of active microwave sensors supported by additional, complementary instruments:
– AMI – active microwave instrument consisting of a synthetic aperture radar (SAR) and a wind scatterometer
– RA – radar altimeter
– ATSR – along-track scanning radiometer
– Gome (ERS-2) – global ozone monitoring experiment
– MWS – microwave sounder
– PRARE – precise range and range rate equipment
– LRR – laser retroreflector
The satellite concept is based on reusing the Multi-mission Platform, developed within the French SPOT programme. This platform provides the major services for satellite and payload operations, in particular attitude and orbit control, power supply, monitoring and control of payload status, and telecommunications with the ground segment.
The Radar Altimeter (RA) is a Ku-band (13.8 GHz) nadir-pointing active microwave sensor designed to measure the return trip time for echoes from ocean and ice surfaces. Functioning in one of two operational modes (ocean or ice) the Radar Altimeter provides information on significant wave height, surface wind speed, sea surface elevation, relating to ocean currents, the surface geoid and tides, and various parameters over sea ice and ice sheets.
The Along-Track Scanning Radiometer (ATSR) combines an infrared radiometer and a microwave sounder for measuring sea surface temperature, cloud top temperature, cloud cover and atmospheric water vapour content. This is used, among other things, to correct altimetry data from path delay due to atmospheric water.
The ERS sensor location system includes two instruments – the Precise Range and Range-rate Equipment (PRARE) and the Laser Retroreflectors (LRR) to provide precise orbit determination for the referencing of height measurements made by the Radar Altimeter. The PRARE has been non-operational since launch, but a description of it is included here for completeness.
The Precise Range and Range-rate Equipment (PRARE) is included for the accurate determination of the satellite’s position and orbit characteristics, and for precise position determination (geodetic fixing).
The LRR is highly accurate but it requires ground stations that are complex to operate, and its use can be restricted by adverse weather conditions. It is used to calibrate the other location system so that the satellite’s orbit can be determined as accurately as possible.