Sea surface temperatures of the coastal zones of France observed by the HCMM satellite

Abstract

The Heat Capacity Mapping Mission experimental satellite was launched in April 1978 and provided data until July 1980. Although the basic mission objective was the measurement of diurnal temperature variations of the earth's surface for soil and geology applications, the characteristics of the heat capacity mapping radiometer onboard the satellite (temperature sensitivity of 0.3°C, instantaneous field of view of 0.5 km) also recommended it for use in oceanographic studies. The data acquired during the period from May 1978 to May 1979 were systematically utilized for evaluation of sea surface temperature in French oceanic regions (North Sea, English Channel, Celtic Sea, Bay of Biscay, and western Mediterranean Sea) and for study of sea surface temperature‐related dynamic phenomena. Comparisons were made of the radiometric performance of the heat capacity mapping radiometer to that of the very high resolution radiometer and the advanced very high resolution radiometer onboard meteorological satellites. They demonstrate the decisive gain in quality of the heat capacity mapping radiometer over the very high resolution radiometer and the similarly improved quality of the heat capacity mapping radiometer and advanced very high resolution radiometer for the observation of mesoscale sea surface temperature features. The utilization of available photographic products proved very suitable, since they had been geometrically corrected and enhanced in the sea surface temperature range, consequently avoiding many of those cases requiring involved computer treatment. On the basis of the interpretation of photographic products, conclusions have been drawn regarding several oceanic phenomena: (1) The thermal effluent of the Rhine‐Meuse system is affected by the residual tidal current of the North Sea. The extent of the offshore diffusion of the effluent is influenced by winds from the northeast and west which, respectively, retard or accelerate the residual current; (2) images exhibiting cold water along the edge of the continental shelf strongly support the hypothesis of a mixing process due to internal waves generated by the action of tidal currents at the edge of the shelf; (3) large‐scale eddy structures detected during the summer in the region of the Mediterranean Sea around 6°E and 38°N may be linked to a phenomenon of barotropic‐baroclinic instability; (4) significant diurnal heating of the surface layer (several degrees Celsius) observed in the Mediterranean Sea is related to the presence of weak winds, leading one to interpret with caution the daytime sea surface temperature satellite observations made during the summer period.