An investigation into the accuracy of surface temperature retrievals from the AATSR

This thesis investigates the accuracy of operational sea surface temperature (SST) and land surface temperature (LST), data from the Advanced Along-Track Scanning Radiometer (AATSR). The study includes some of the first in situ validation results for these data sets, and forms an integral part of the overall AATSR validation programme. In addition, a comprehensive sensitive study of the response of these retrievals to changes in atmospheric and surface conditions is also presented as in aid to interpreting validation results. AATSR SSTs recorded during 2003 have been validated over the Caribbean sea, using in situ observations of SST from the Marine-Atmosphere Emitted Radiance Interferometer (M-AERI). This validation experiment, which extends over a full year, is the most extensive yet performed for any of the ATSR instruments (ATSR-1, ATSR-2 and AATSR) using in situ SSTs derived from radiometric measurements. These data also provide a first opportunity to study seasonal biases using observations of this type. The results demonstrate that clear-sky SSTs obtained using the unique dual-viewing geometry of the AATSR agree with the in situ data to within 0.3 K. Nadir-only retrievals performed using three channels also provide SSTs that approach this accuracy, but the split-window retrievals are found to be warm-biased by ∼0.6 K. When tropospheric dust aerosol is present, the accuracy of the retrieved SSTs is reduced, with the nadir-view SSTs becoming cold biased and the dual-view SSTs, warm biased. For the first time, the potential for validation of LST over heterogeneous land sites is also explored. Two methodologies are presented for upscaling point in situ LSTs to the 1-km spatial scale of the AATSR, together with initial validation results over a field site in Morocco, which suggest that the AATSR LSTs are warm-biased by at least 0.6 K over this site. The findings of this study suggest that validation over heterogeneous sites is possible for situations where the variation of LST is characterised by several in situ point observations of LST..