The ATSR (Along Track Scanning Radiometer) instruments produce infrared images of the Earth at a spatial resolution of one kilometre. The first ATSR instrument, ATSR-1, was launched on board the European Space Agency's (ESA) European Remote Sensing Satellite (ERS-1) in July 1991, as part of their Earth Observation Programme. An enhanced version of ATSR, ATSR-2, was successfully launched on board ESA's ERS-2 spacecraft on 21st April 1995. ATSR-2 is equipped with additional visible channels for vegetation monitoring. The AATSR (Advanced Along Track Scanning Radiometer) instrument has been successfully launched on board the ENVISAT spacecraft on 1st March 2002 at 01:07 GMT from the Kourou spaceport in French Guiana.
Satellite measurements of the surface of the Earth are inevitably affected by the passage of radiation through the atmosphere. The dual view design of ATSR makes it possible to estimate and correct for such atmospheric effects. The two views result from the instrument's conical scanning mechanism. Each scan takes readings from the nadir position and then sweeps round to take measurements from a point about 900 km along the satellite's track. A few minutes after acquiring the forward view, the satellite passes over the same spot and takes readings for the nadir view. As the two views of the same scene are taken through different atmospheric path lengths, it is possible to estimate both the surface and the atmospheric contribution to the measured radiance.
EODG uses data from ATSR-2 and AATSR as input to the ORAC retrieval scheme to determine the microphysical properties of clouds and aerosols. Results from this work are vital for estimating long-term trends in atmospheric behaviour and so to better understand anthropogenic influence on the atmosphere.