Autonomous Measurements of Sea Surface Temperature Using In Situ Thermal Infrared Data

In situ and autonomous measurements of sea surface temperature (SST) have been performed with a thermal infrared radiometer mounted on a fixed oil rig. The accuracy limit was established at (plus-minus) 0.3 K for these SST measurements in order to meet the requirements of the Tropical Ocean Global Atmosphere (TOGA) program for global climate research and the Soil Moisture and Ocean Salinity (SMOS) mission for salinity retrieval. With this aim, the optimal observation angle and spectral channel for SST measurements have been identified. Then, a methodology has been developed for the radiometer calibration and the emissivity correction, including the reflection of the downwelling sky radiance, which was directly measured simultaneously to the sea surface observation. The effect of the atmospheric path between the sea surface and the sensor has been also studied and found negligible for the particular viewing conditions. A sensitivity analysis of the proposed methodology has shown a precision of (plus-minus)0.15 K in the retrieved SST. Finally, the measured SSTs have been validated with coincident buoy temperatures, resulting in an average difference of 0.0 K and a standard deviation of (plus-minus)0.2 K.