A reprocessing for climate of sea surface temperature from the along-track scanning radiometers: Basis in radiative transfer

Abstract

We present new radiative transfer simulations to support determination of sea surface temperature (SST) from Along Track Scanning Radiometer (ATSR) imagery. The simulations are to be used within the ATSR Reprocessing for Climate project. The simulations are based on the “Reference Forward Model” line-by-line model linked with a sea surface emissivity model that accounts for wind speed and temperature, and with a discrete ordinates scattering model (DISORT). Input to the forward model is a revised atmospheric profile dataset, based on full resolution ERA-40, with a wider range of high-latitude profiles to address known retrieval biases in those regions. Analysis of the radiative impacts of atmospheric trace gases shows that geographical and temporal variation of N₂O, CH₄, HNO₃, and CFC-11 and CFC-12 have effects of order 0.05, 0.2, 0.1K on the 3.7, 11, 12μm channels respectively. In addition several trace gases, neglected in previous studies, are included using fixed profiles contributing ~0.04K to top-of-atmosphere BTs. Comparison against observations for ATSR2 and AATSR indicates that forward model biases have been reduced from 0.2 to 0.5K for previous simulations to ~0.1K.