SENSITIVITY OF SATELLITE MULTICHANNEL SEA-SURFACE TEMPERATURE RETRIEVALS TO THE AIR-SEA TEMPERATURE DIFFERENCE

The advanced very high resolution radiometer multichannel sea surface temperature (MCSST) retrieval technique provides global algorithm accuracy statistics generally showing a bias of less than 0.1-degrees-C and an rms error of less than 0.7-degrees-C when compared to colocated drifting buoy in situ data in the absence of aerosols. This remaining error is not always random but is shown to be correlated to the air-sea temperature difference. The MCSST technique is modeled and then compared to in situ data to show this dependency. Atmospheric radiative transfer calculations are used to provide a simulation of satellite retrieval sensitivity to air-sea temperature differences. Buoy sea surface temperature (SST) and air temperature observations are then presented as experimental verification of the simulation results. Retrieval errors depend both on the mean air-sea temperature difference conditions present in the data set used to empirically derive the algorithm and on the changes in air-sea temperature difference conditions relative to the derivation data set mean conditions. Retrieval error is found to respond linearly with air-sea temperature difference changes. MCSST retrieval errors of 1.0-degrees-C can occur for air-sea temperature difference changes of 7-degrees-10-degrees-C from mean conditions when the dual-window (channels 3 and 4) or triple-window (channels 3, 4, and 5) algorithms are used. The split-window (channels 4 and 5) MCSST algorithm is shown to be less sensitive to air-sea temperature differences. Cross-product SST (CPSST) and nonlinear SST (NLSST) algorithms are also examined. These algorithms generate results similar to the MCSST algorithm for the dual- and triple-window equations. However, the CPSST and NLSST split-window algorithms demonstrate greater sensitivity to air-sea temperature difference changes than do the MCSST split-window algorithm. Retrieval errors of 1-degrees-C can occur for air-sea temperature difference changes of 10-degrees-12-degrees-C from mean conditions. Users of satellite SST retrievals in regions that experience large fluctuations in air-sea temperature difference should be aware of this possible error source.