Six years of OSI-SAF METOP-A AVHRR sea surface temperature

Abstract The Ocean and Sea Ice Satellite Application Facility (OSI SAF) has been producing full resolution global Sea Surface Temperature (SST) from the METOP-A Advanced Very High Resolution Radiometer (AVHRR) since July 2007. The SST operational processing and the validation scheme have remained unchanged for more than 6 years. The global validation results against measurements are stable over time. Night-time METOP-A SSTs differ from drifting buoy SSTs by − 0.05 K in average with a standard deviation of 0.44 K and the daytime values are respectively 0.09 K and 0.56 K. Seasonal statistics have been calculated on a global regular 5-degree grid for a 6-year period to review the main biases and their characteristics. There is evidence of regional and seasonal biases, indeed the multispectral regression algorithms are known (to a various degree depending upon specific implementation) to have limitations in handling the variety of atmospheric absorption conditions encountered over the global ocean. This problem has been solved for the OSI SAF geostationary SST chain by adopting a Numerical Weather Prediction (NWP) profile based correction method. The same approach has been tested on a prototype chain ingesting METOP-A data and gives encouraging results. It will be used in the new polar orbiter chain under development at OSI SAF, that will process METOP-B data. An application example of METOP-A SST time series is given by analyzing the inter-annual variability of Arctic Ocean SST in relation with the ice coverage variability in September. The METOP-A time series gives consistent results when compared to other observations or model outputs.