Multifrequency scatterometer measurements of Baltic Sea ice during EMAC-95

Abstract

As part of the European Multi-Sensor Airborne Campaign on Snow and Ice 1995 (EMAC-95), the radar signatures of smooth low-salinity level ice in the Gulf of Bothnia were measured by means of a ship mounted scatterometer. The scatterometer was operated at 1.25, 2.6, 5.4 and 10GHz ( L -, S -, C -, and X -band) at incidence angles from 20degrees to 60degress. Various in situ snow and ice parameters were acquired during the field work. Utilising the ranging capabilities of the scatterometer system, the travel times of the radar returns are analysed at the different frequencies in order to locate the dominant scattering contributions as a function of depth in the ice. Model predictions which are based on the in situ snow and ice properties are compared with the measured backscattering coefficients in order to determine the scattering mechanisms of the dominant radar returns. Experimental and model results show that the backscattering responses at X -band are mainly caused by volume inhomogeneities in the uppermost part of the ice, and at C - and S -band by the roughness of the snow-ice interface. At L -band, however, dominant radar returns can originate also from the interior of the ice, probably from the ice-water interface, which is substantiated at smaller incidence angles. Implications of the presented results are discussed.