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The SeaWinds instrument on the QuikSCAT satellite was designed to measure near surface winds over the ocean; however, this remarkable remote sensing instrument has proven very useful in polar ice studies. Unlike previous radar scatterometers which were limited to 2 or 3 azimuth angles, the Ku-band SeaWinds instrument uses a circular scanning pencil beam, allowing it to make radar backscatter measurements from all azimuth angles. This geometry makes it an ideal candidate for studies of azimuth modulation of the normalized radar cross section of natural surfaces. Previous studies
have observed a second order azimuth modulation of radar backscatter on the Antartic ice sheet, which has been related to wind-generated sastrugi (snow dunes) on the surface. In this paper we use SeaWinds data to make more detailed studies of the azimuth modulation in both Antarctica and Greenland where little has been done. Using the higher azimuth resolution possible with SeaWinds, we find that the azimuth variation of the backscatter is better described using a fourth order model in areas with the highest modulation. The orientation of these fourth order terms appears to be highly correlated to the katabatic wind direction. Azimuth modulation is as observed over Greenland, but it is much smaller than over Antarctica. Comparing SeaWinds and ERS-1/2 satterometer mode data we examine the frequency dependence, finding the modulation larger at C-band than Ku-band. The largest azimuth modulation in Greenland is observed in the transition region between dry snow and percolation zones.
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