AATSR

The Advanced Along Track Scanning Radiometer (AATSR) is one of the Announcement of Opportunity (AO) instruments on board the European Space Agency (ESA)'s Envisat satellite.

This instrument is a multi-channel imaging radiometer with the principal objective of providing data concerning global Sea Surface Temperature (SST) to the high levels of accuracy and stability required for monitoring and carrying out research into the behaviour of the Earth’s climate.

AATSR can measure Earth's surface temperature to a precision of 0.3 K (0.5 °F), for climate research. Among the secondary objectives of AATSR is the observation of environmental parameters such as aerosols, clouds, fires, gas flares, water content, biomass, and vegetal health and growth. AATSR is the successor of ATSR-1 and ATSR-2, payloads of ERS-1 and ERS-2.

The required accuracies are better than 0.3 °C with a stability approaching 0.1 °C /decade. Because of its wide angle lens it is possible to make very precise measurements of atmospheric effects on how emissions from the Earth's surface propagate.

In order to achieve this accuracy while viewing the Earth's surface through the atmosphere, AATSR views the surface at two angles, one close to the nadir (immediately below the satellite) and the other along the satellite track at close to 55° from the nadir, thereby providing two views of each point on the Earth's surface, each with a different effective atmospheric thickness. This dual-view system enables a particularly accurate estimate to be made of the signal degradation due to atmospheric absorption and scattering.

AATSR also embodies an exceptionally precise and stable on-board calibration system, comprising two reference targets specially designed for high uniformity and stability. These two targets, known as 'black bodies' are maintained at temperatures near to the extremes of the Earth temperatures as measured by AATSR and they are both viewed during each scan cycle of the instrument. This calibration system ensures that measurements of thermal radiation from the Earth’s surface are properly calibrated and do not rely on ground-based measurements, although such measurements are continually used to evaluate AATSR’s performance.

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