Mitigation of the AVHRR instrumental issues in historical SST retrievals for the NOAA AVHRR GAC SST RAN2

The 2(nd) Reanalysis (RAN2) of the 4 km Global Area Coverage (GAC) data of the Advanced Very High-Resolution Radiometers (AVHRR/2s and /3s) flown onboard ten NOAA satellites from Sep'1981 - present was performed, and global sea surface temperature (SST) dataset created with the NOAA Advanced Clear-Sky Processor for Oceans (ACSPO) enterprise system. The RAN2 dataset includes two SST products retrieved in a full similar to 3,000 km AVHRR swath: "Subskin" (highly sensitive to true skin SST) and "Depth" (agreeing much closer with in situ SST, but with a reduced sensitivity). The performance of both RAN2 SST products were improved compared with RAN1, by mitigation of several AVHRR sensor issues. The long-term AVHRR calibration trends were mitigated by daily recalculation of the regression coefficients using matchups with in situ SSTs collected within limited time windows centered at the processed day. Biases with respect to in situ SST were further minimized on a monthly basis by adjustment of the offsets of regression equations based on 31-day moving windows. Massive cold SST outliers, caused by nighttime Sun impingements on the AVHRR's black body calibration targets, were corrected by interpolating the L1b calibration coefficients between the unaffected parts of the orbit. The Earth view pixels affected by stray sunlight were identified and screened out using the elevated signal in the AVHRR band 2 (0.86 mu m). This paper describes the methodology and demonstrates its effects on the RAN2 SST.