Bias Adjustment of AVHRR SST and Its Impacts on Two SST Analyses

Sea surface temperature (SST) observations from satellite-based Advanced Very High Resolution Radiometer (AVHRR) instrument exhibit biases. Adjustments necessary for removing the AVHRR biases have been studied by progressive experiments. These experiments show that the biases are sensitive to various parameters, including the length of the input data window, the base-function empirical orthogonal teleconnections (EOTs), the ship–buoy SST adjustment, and a shift in grid system. The difference in bias adjustments due to these parameters can be as large as 0.3°–0.5°C in the tropical Pacific at the monthly time scale. The AVHRR bias adjustments were designed differently in the daily optimum interpolation SST (DOISST) and the Extended Reconstructed SST datasets that ingest AVHRR SSTs (ERSSTsat). The different AVHRR bias adjustments result in the differences in SST datasets in DOISST and ERSSTsat. Comparisons show that the SST difference between these two datasets results largely from the difference in the AVHRR bias adjustments and little from SST analysis methods in the Niño-3.4 region, as well as in the global oceans. For example, the average difference of the Niño-3.4 SSTs between DOISST and ERSSTsat is approximately 0.12°C due to the bias adjustments and is about 0.01°C due to the analysis methods. This study finds that the DOISST datasets can be improved by using the revised AVHRR bias adjustment of a wider input data window, updated EOTs, and a shifted grid system in DOISST. Improvements can also be made by including a ship–buoy SST adjustment, a zonal SST adjustment, or revised EOTs without damping in the high latitudes in ERSSTsat.