SAR INTERFEROMETRY OVER BALTIC SEA-ICE

SAR interferometry (InSAR) offers new interesting possibilities for re search in sea ice radar scattering and sea ice mechanics. A case study of this is presented from the Baltic Sea in late March 1992. Interfer ometric coherence is mainly dependent of the temporal characteristics of the scattering sources in sea ice. Different areas with different s cattering 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 b ackscatter areas are more unstable than low backscatter areas. Over ar eas with surface roughness scattering, the scattering is relatively st able and also that a snow cover seems to retain the coherence over suc h areas. Interferometric phase measurements are dependent on small def ormations of the ice pack. Fast ice which is (nearly) stationary exper iences small discontinuous slips and deformations. Interferometric pha se measurements are very sensitive to these slips, displacements and d eformations and will provide new insight into the rheology for fast ic e 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 flee compressions have been obser ved and the strains are believed to be viscous with a viscosity value at approximately 10(13)-10(14) kg (ms). Both the interferometric phase and the coherence measurements over ice are believed to be of great v alue in future backscattering models and sea ice mechanics models.