Ice flow properties derived from ICESat surface topography in polar ice sheets

A major difficulty in numerical modeling of ice sheets is a lack of sufficiently precise information on the flow properties. Analysis of the detailed variations in the ice sheet elevation profiles against bedrock topography provides valuable means of determining ice flow properties. In this study, the power spectral analysis of the detailed ICESat surface undulation data against available bedrock profiles was performed along selected sections near flow-lines over both Antarctica and Greenland. The spectra of the surface undulations are characterized by a minimum damping indicated by a peak value of the power with wave-length of several km, whereas the magnitude of the spectra for the bedrock increases with the wave-length. By using balance velocity and a mean damping factor with wave-length of 20-40 km, the mean effective ice viscosities are estimated and compared with values from laboratory ice deformation tests. The increased departure from inland to coast between topography and laboratory derived viscosities for isotropic polycrystalline ice may indicate systematic changes in the development of crystal anisotropies and the amount of basal sliding.