Calibration of the AATSR instrument

Abstract The Advanced Along Track Scanning Radiometer (AATSR) on ESA's ENVISAT mission is the latest in a series of instruments designed to measure global sea-surface-temperatures to an accuracy of 0.3K and to monitor global vegetation coverage and cloud properties. The accuracy of the SST and other scientific products depends on the accuracy of the top-of-atmosphere radiometric measurements. To ensure that AATSR meets its scientific goals, the instrument is equipped with precision on-board calibration targets. To verify the accuracy of the on-board calibration, a thorough pre-launch calibration exercise was performed, covering field-of-view measurements, visible and infrared radiometric calibrations. The radiometric responses of the visible/near infrared channels were measured, and the in-flight VISible Calibration unit (VISCAL) was calibrated. The calibrations of the thermal infrared channels were verified over a range of target temperatures between 210K to 315K and corrections derived for detector non-linearity. Tests were also performed to verify freedom from any significant scan dependent variations or effects due to changes in the thermal environment.