Summary
There is a distinct directional anisotropy in microwave backscatter from the surface of the East Antarctic ice sheet as measured by the C-band wind scatterometer carried by the ERS-1 satellite. The anisotropy is characterised by an amplitude and an orientation which correspond to the amplitude of variation in backscatter coefficient with azimuth and the orientation or look direction for minimum backscatter respectively. The anisotropy is apparent in the differences between the backscatter measurements in the three look directions of the antennas of the instrument. In polar regions, the close spacing of neighbouring orbits of the ERS-1 satellite and the 500 km wide swath of the scatterometer instrument provide many backscatter measurements of a given location with a large range of incidence angles and multiple look directions. The backscatter coefficients for any point on the ice sheet exhibit an approximately linear dependence on incidence angle. The azimuthal variation about a mean value is described by a bi-sinusoidal function of the antenna look direction. Mean values of the amplitude and orientation of the anisotropy are derived by a least squares solution incorporating the many observations acquired within a given time interval at a point. The amplitude and orientation of the anisotropy vary systematically with position on the ice sheet. The amplitude of the anisotropy has values typically in the range 1.0 to 3.5 dB, and extreme values up to 5.5 dB. For most of the ice sheet area there is very little variability in monthly mean values of amplitude and orientation of the anisotropy. Regions exhibiting the largest amplitude of the anisotropy appear to be associated with winds of more persistent direction on the plateau slope. This is most apparent in the sector from 80°E to 150°E above 1500 m elevation and up to 3000-3500 m. It is strongest in two areas, one between longitudes 80°E and 90°E and latitudes 69°S and 75°S, and the other between