An Accuracy Assessment of Aatsr Lst Data Using Empirical and Theoretical Methods

The Advanced Along-Track Scanning Radiometer (AATSR), onboard ESA’s Envisat Satellite, is a precision radiometer that provides data from which global observations of land surface temperature (LST) can be derived. These LST data are retrieved using a nadir-only split window algorithm, with a target accuracy of 2.5 K during the day and 1.0 K at night. The algorithm will also be applied operationally to data recorded by the AATSR’s predecessors, ATSR-1 (ERS-1) and ATSR-2 (ERS-2), leading to a > 15-year record of global LST data. We present the results of comparisons between operational AATSR LST retrievals and collocated in situ data that have been recorded continuously at three sites over at least one year. The exercise provides an excellent opportunity to assess the long-term accuracy of the satellite LST data. The results demonstrate that, although the overall agreement between the AATSR and in situ data is close to the target accuracy of the retrieval scheme, there are some notable seasonal biases in the data. These seasonal biases are also apparent in AATSR LST retrievals that have been simulated using a radiative transfer model with atmospheric and surface parameters that are appropriate for each of the sites, over one year. Examination of the variation of simulated and observed bias with LST, water vapour and atmospheric temperature indicates that the primary source of bias is most likely to be the current operational algorithm’s high sensitivity to these parameters.