Evaluation and Quality Control of in situ SSTs for Use in the Calibration and Validation of Satellite Retrievals at NESDIS

In situ sea surface temperatures (SST) are used for calibration and validation (Cal/Val) of satellite retrievals at NESDIS. This study analyzes in situ SSTs available from three data sets: the NCEP GTS (since 1991), the ICOADS release 2.4 (since 1980), and the US GODAE/FNMOC (since 1998). Comparisons show that most reports in the ICOADS and FNMOC are of the same origin as NCEP GTS. Quality control (QC) information is either not available on some data sets (NCEP), not well documented (FNMOC), or non-uniform (ICOADS, FNMOC). Therefore, basic QCs were implemented and uniformly applied to all SSTs.

All analyses are stratified by major types of in situ platforms including ships, drifters, and moored buoys, the latter being further subdivided into tropical and coastal. Ship platforms overwhelmingly prevailed before 1990 but then declined, whereas the number of drifters significantly increased, as did their reporting density. Both of them provide comparable coverage and well sample the whole SST range, while drifter distribution is much more geographically uniform than ship. For drifters and tropical moorings, global mean biases with respect to daily Reynolds SST are within several hundredths of a Kelvin, and standard deviations (SD) are approximately 0.3 K. Coastal moorings are more biased and noisier and additionally show a pronounced seasonal cycle in the number of reports, biases, and SDs. Ships are only slightly biased with respect to daily Reynolds SST by +0.1 K but show a large SD of about 1.2 K.

Bayesian QC aimed towards flexibility, scalability, and consistency with the practices adopted by the meteorological, oceanographic, and numerical weather prediction communities (e.g., Lorenc and Hammon, 1988; Ingleby and Haddleston, 2007) are also analyzed in this study. The objective is to implement a near-real time QC as a front-end to the NESDIS operational Cal/Val system. Progress towards this objective is also described.