In Situ Validation of Satellite Sea Surface Temperature Measurements in a Northern California Upwelling Area

Abstract

This study validates Advanced Very High Resolution Radiometer (AVHRR) satellite sea surface temperature (SST) data with in situ data from oceanographic buoys in the Point Arena upwelling area, offshore of northern California. Sea surface temperature in this area is often colder, and more spatially and temporally variable than nearby deep ocean waters. Global AVHRR data is validated at the 25 km scale. It is possible that SST in coastal upwelling areas may not resolve well at this scale. This study uses a 1 km scale to explore AVHRR error under conditions where satellite SST data has been shown to vary in previous studies: day/night, season, and under low, moderate and high wind speeds. A data set of 25,000 matchups over 21 years was analyzed. An overall systematic error of 0.47°C (MBE) was found. Analysis of matchup subsets found higher error during daytime, low wind speeds and the relaxation season. Several systematic errors and possible causes are discussed. An adjustment factor is provided that can be applied to future AVHRR SST to account for the bias found in this study.