Radar backscatter across the Gulf Stream sea surface temperature front

Abstract

Ku-band backscatter responses to frontal sea surface temperature (SST) changes are studied and applications of a high-resolution scatterometer to remote sensing of an SST front are suggested. Ocean backscatter signatures were measured with an airborne Ku-band scatterometer across the Gulf Stream SST front during the Surface Wave Dynamics Experiment. Oceanic and atmospheric parameters were measured by buoys, by the Scanning Radar Altimeter, and by the Advanced Very High Resolution Radiometer, and the surface current fields analyzed by the Fleet Numerical Meteorology and Oceanography Center were obtained. Vertical polarization backscatter difference across the SST front with an SST difference of 9/spl deg/C is more than 5 dB in several flight lines. Large horizontal polarization backscatter changes are also observed across the SST front with an SST difference approximately one-half of that in the vertical polarization backscatter case. Corresponding wind speed differences cannot account for the large backscatter changes in view of Seasat-A Satellite Scatterometer (SASS) geophysical model functions depending only on neutral wind velocity. For both polarizations, upwind backscatter on the cold side is smaller than or close to crosswind backscatter on the warm side for incidence angles larger than 20/spl deg/ and smaller than 60/spl deg/. This suggests that the SST front can be detected with backscatter measured by a spaceborne radar at a fixed azimuth angle even if wind directions are different over the cold and warm sides.