The accuracy of the AATSR sea surface temperatures in the Caribbean

Abstract

The Along-Track Scanning Radiometer (ATSR) series of instruments provides the means to obtain accurate measurements of sea surface temperature (SST), with a target total uncertainty of ± 0.3 K, 1 σ. In this paper, we present validation results from 1 year of comparisons between 1 km resolution SSTs derived from the third instrument in the series, the Advanced ATSR (AATSR), and in situ measurements obtained during 2003 from the Marine-Atmospheric Emitted Radiance Interferometer (M-AERI) over the Caribbean. Our dataset consists of 99 cloud-free matchups, 25 of which are two-channel SST retrievals (daytime) and 74 three-channel SST retrievals (nighttime). Validation results for both dual- and nadir-view SSTs for these matchups are presented. We demonstrate that the dual–nadir SST measurement difference (D–N) can be used to classify matchups and attribute the likely cause of a particularly high D–N to outbreaks of Saharan dust. Under conditions of ‘normal’ D–N, the bias and standard deviation of the two- and three-channel dual-view retrievals is − 0.05 K and 0.26 K, and 0.02 K and 0.25 K, respectively. Dual-view SSTs obtained when the D–N is high over the Caribbean exhibit significant warm biases of 0.60 K and 0.32 K for two- and three-channel retrievals, respectively. Cool biases, with respect to the bias for ‘normal’ D–N, are observed in the nadir three-channel (N3) SSTs; for matchups with high D–N, the bias and standard deviation are − 0.16 K and 0.31 K, compared with 0.14 K and 0.24 K for ‘normal’ D–N. The distribution of the nadir two-channel retrievals is non-Gaussian and the apparent accuracy is comparatively poor, demonstrating clearly the advantages of using a sensor with dual-viewing capabilities to obtain a superior atmospheric correction, particularly when data from an additional short-wave infrared channel (e.g. at 3.7 μm) is not available.