THE EMPIRICAL ANGULAR FUNCTION-APPROACH - TESTING SEA-SURFACE TEMPERATURE SATELLITE RETRIEVALS

Recently, a statistical procedure was proposed to analyze the angular effect in the NOAA Advanced Very High Resolution Radiometer (AVHRR) br ightness temperatures. The estimated empirical angular functions (EAF) over the oceans allow one to check the algorithms for the sea surface temperature (SST) and the column water vapor content when the observa tion geometry is variable, as well as to test angular methods of SST r etrieval. The EAF approach has been previously applied to the analysis of the AVHRR brightness temperatures in channels 3 and 4 and dual-win dow SST over the tropical Atlantic in June 1987 and December 1988 from NOAA-10 and NOAA-11, respectively. Here, it is extended to estimate t he accuracy of the split-window sea surface temperature and atmospheri c water vapor retrievals from NOAA-9 over the tropical and North Atlan tic in July 1986. The authors confirm the previously drawn conclusion that in a general case no angle-independent coefficients in a linear S ST retrieval algorithm can provide angle-invariant retrievals. More re cent operational NOAA angle-dependent algorithms have been shown to im prove retrievals in the Tropics. In high latitudes, they seem to sligh tly overcorrect the angular effect. Using satellite data of higher spa tial resolution with better radiometric accuracy is expected to improv e the accuracy of the EAFs and the reliability of the conclusions.