On the suitability of global algorithms for the retrieval of SST from the north Indian Ocean using NOAA/AVHRR data

The errors associated with the SST retrievals from the north Indian Ocean, using global multichannel sea surface temperature (MCSST), nonlinear sea su rface temperature (NLSST), and Pathfinder sea surface temperature (PFSST) a lgorithms are analysed using satellite-sea-truth matchups for NOAA-9 and NO AA-11. The trends associated with the SST retrievals with respect to variou s independent parameters and simple statistics are analysed to assess the p erformance of the algorithms. The MCSST and NLSST retrievals have undesirab ly large trends associated with surface temperature, satellite scan geometr y and scan time (day/night); SST retrievals using PFSST show the lowest tre nds. The simple statistics, mean, and rmsd, are worst for MCSST (0.6 and 1. 3 degrees C); they are unsatisfactory for NLSST (0.4 and 0.7 degrees C) and PFSST (0.4 and 0.7 degrees C) also. Considerable improvement in statistics and trends are achievable by regionally optimizing the algorithm coefficie nts. The mean and RMSD of residuals drop to more than 50% of the values obt ained by the use of global coefficients. Regionally optimized NLSST appear to be the better algorithm for the north Indian Ocean in the absence of tim e-dependent regional coefficients suggested by PFSST.