The accuracy of SST retrievals from Metop-A IASI and AVHRR using the EUMETSAT OSI-SAF matchup dataset

Abstract

Skin sea surface temperatures (SST) from the infra-red atmospheric sounding interferometer (IASI) have been available in the Group for High Resolution Sea Surface Temperatures (GHRSST) L2Pcore format from the EUMETSAT data centre since March 2011. IASI SSTs, produced from version 5.0 of the IASI Product Processing Facility (PPF), have been validated against drifting buoy SSTs and compared to AVHRR SSTs contained with the EUMETSAT Ocean and Sea-Ice Satellite Application Facility (OSI-SAF) matchup dataset, over the period October 2010 to July 2011. The IASI SSTs were found to be of good quality with a slight cool bias compared to drifting buoys (bias −0.32K, σ 0.32K) and AVHRR SSTs (bias −0.35K, σ 0.30K). The highest quality IASI SSTs had a bias compared to drifting buoys of −0.16K (σ 0.33K). Using three-way collocations of differences between IASI, AVHRR, and drifting buoy SSTs gave IASI SSTs to have a standard deviation of error of 0.28K, AVHRR 0.13K, and drifting buoys 0.20K. IASI and AVHRR SSTs were found to be complementary to each other, giving benefit in different locations. Some residual cloud contamination was observed in the IASI SSTs, contributing to the slight cool bias. For collocations deemed likely to be 100% cloud free, the IASI bias reduces to −0.25K (σ 0.39K) using quality levels 2 to 5, and a bias of −0.09K (σ 0.34K) for observations with quality level 5. In addition, some evidence of increased uncertainties due to comparing point buoy observations with areal satellite observations was seen in the daily statistics for all observation types.