The Validation of ATSR Using Aircraft Radiometer Data over the Tropical Atlantic

Abstract

The First ATSR Tropical Experiment was carded out in November 1991 over the tropical Atlantic to validate daytime measurements of sea surface temperature (SST) made by the Along Track Scanning Radiometer (ATSR) on the European remote sensing satellite, ERS-1. An airborne infrared radiometer with channels at 11 and 12 µm spectrally matched to those on the ATSR was used to make nadir, 60° to nadir, and zenith view radiance measurements at a number of different altitudes from 70 m to 8 km above the sea surface. The effect of stratospheric aerosols on the ATSR radiances, due to the June 1991 eruption of Mount Pinatubo, was quantified as nadir view brightness temperature deficits of up to 0.6 K at 11 µm. ATSR retrievals of SST (using both nadir and forward views) were compared with SSTs inferred from low-level radiance measurements of the sea surface that were unaffected by atmospheric absorption. ATSR SSTs retrieved using the nadir only views had negative (i.e., cold) biases of about 2 K. If the forward view was also included in the retrieval, the negative biases reduced to approximately 0.7 K. Radiance profiles through the atmosphere were also obtained for comparison with those computed by the Rutherford Appleton Laboratory radiative transfer model, which had been used to Venerate the ATSR SST retrieval coefficients. These showed that a positive (warm) bias of 1.5 K exists between the model and nadir view aircraft radiometer measurements at the 6-km altitude for these tropical atmospheres.