Summary
Measurements of the microwave backscatter from the Antarctic ice sheet have been obtained by the single-sided, right-looking, C-band wind scatterometer carried by the ERS-1 and 2 satellites and by the dual-sided, ku-band NSCAT instrument on ADEOS. The different operating wavelengths and antenna geometry of the two types of instrument facilitates an investigation of the influence of the observing system on the backscatter measurements, system performance, and the nature of observed anisotropy. The backscatter exhibits a character which varies with the near surface properties of the snow cover and systematically with location on the ice sheet. There is a distinct directional asymmetry in the intensity of the backscatter which can be detected and measured over the whole ice sheet and related to the persistent wind field. Analysis of long time series of backscatter measurements shows that the asymmetry effect appears to be stable, even in areas where the signal is weak. Its orientation and amplitude are compared to ground observations of the orientation of surface roughness elements. The axis of the minimum in the directional asymmetry coincides with the longitudinal axis of surface microrelief, mainly in the form of snow dunes and sastrugi, and with the mean wind observed at automatic weather stations. In addition to the surface features, the scatterometers actually detect structures related to the surface roughness which have been preserved within the snow cover through burial by progressive snow accumulation and thus provide a time-integrated result. This detection of the local mean orientation of the microrelief allows information to be derived about the direction and strength of the persistent surface (katabatic) wind field. Regions exhibiting the largest amplitude in the asymmetry are associated with areas of greatest roughness and strongest or most stable/persistent winds. Similar orientations are obtained from the two different