Sensitivity of satellite multichannel sea surface temperature retrievals to the air‐sea temperature difference

Abstract

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°C and an rms error of less than 0.7°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°C can occur for air‐sea temperature difference changes of 7°–10°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°C can occur for air‐sea temperature difference changes of 10°–12°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.