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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. [ABSTRACT FROM AUTHOR]

SAR interferometry (InSAR) offers new interesting possibilities for research in sea ice radar scattering and sea ice mechanics. A case study of this is presented from the Baltic Sea in late March 1992. Interferometric coherence is mainly dependent of the temporal characteristics of the scattering sources in sea ice. Different areas with different scattering properties were examined and the present data indicates that more field data is necessary to fully understand the InSAR coherence over sea ice. However, some interesting features were noted. Over low-salinity ice, backscattering and coherence seems to be related, high backscatter areas are more unstable than low backscatter areas. Over areas with surface roughness scattering, the scattering is relatively stable and also that a snow cover seems to retain the coherence over such areas. Interferometric phase measurements are dependent on small deformations of the ice pack. Fast ice which is (nearly) stationary experiences small discontinuous slips and deformations. Interferometric phase measurements are very sensitive to these slips, displacements and deformations and will provide new insight into the rheology for fast ice and how the fast ice starts to move. How the fast ice starts to move is one of the major problems in sea ice mechanics research and there is not much earlier data on the subject. In the present case, the ice was nearly stationary as the stresses were below the yield limit under the low forcing conditions. Two ice floe compressions have been observed and the strains are believed to be viscous with a viscosity value at approximately 1013-1014kg (ms). Both the interferometric phase and the coherence measurements over ice are believed to be of great value in future backscattering models and sea ice mechanics models. [ABSTRACT FROM AUTHOR]