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Envisat's AATSR preparing for thermal vacuum test at RAL
The primary scientific objective of the Advanced Along Track Scanning Radiometer (AATSR) is to provide sea surface temperature measurements with the precision and accuracy required for climate research (+/- 0.3 °K). It establishes continuity of the ATSR-1 and ATSR-2 data sets (on ERS-1 and ERS-2) leading to the production of a unique 10 year record of global sea surface temperatures.
The first objective is to develop and exploit the science of quantitative remote sensing of land surfaces, particularly vegetation. The land and cloud measurement objectives are met through the use of an additional visible focal plane assembly, which leads to indications of:
- vegetation biomass
- vegetation moisture
- vegetation health and growth stage
These parameters are used to derive global vegetation indices, using established relationships, modified to incorporate the added information from AATSR's two-angle view. The visible channels are also used to measure cloud parameters, like water/ice discrimination, and particle size distribution.
The principle of removing atmospheric effects in sea surface temperature measurements by viewing the sea surface from two angles is what characterises the family of (A)ATSR instruments.
Global image of AATSR data
The sea surface temperature (SST) is one of the most stable of several key geographical variables which, when determined globally, characterise the state of the Earth's atmospheric system. The precise measurement of small changes in SST provide an indication of quite significant changes in ocean/atmosphere heat transfer rates, especially in the tropics.
Additionally, it is known that small amplitude anomalies occurring in specific areas are sometimes associated with massive atmospheric perturbations, leading to widespread and damaging changes in the global weather system. For example, the 'El Niño' anomaly in the tropical east Pacific is associated with a reversal of the atmospheric 'Walker Circulation'. This in turn creates widespread perturbations to the global weather system. The exact causal relationships between such phenomena are not fully understood, but a significant 'El Niño-like event can evolve from an SST anomaly of 2-3K, and therefore the ability to detect, for example, a 10% change in the anomaly field requires measurements of the accuracy only provided by the (A)ATSR series of instruments.
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