OBSERVATIONS OF THE ANTARCTIC ICE-SHEET WITH THE SEASAT SCATTEROMETER- RELATION TO KATABATIC-WIND INTENSITY AND DIRECTION

The Seasat A satellite scatterometer radar, initially designed to meas ure ocean-wind intensity and direction, also provided observations on the Antarctic ice sheet. The signal of the back-scatter coefficient de creases strongly from 10 to -20 dB when the incidence angle of the obs ervations increases from 0-degrees to 65-degrees. An additional 5dB si gnal is found, which is correlated with the direction and intensity of katabatic winds, independent of the incidence angle and polarization of the signal. By using simplified models of the volume-scattering wit hin the snowpack (which is mostly sensitive to snow grain-size) and su rface-scattering from the air-snow interface (which depends on roughne ss), it is evident that the signal of the scatterometer could result f rom the effects of snow dunes at low incidence angle, and of micro-rou ghness and volume back-scatter at incidence angles greater than 25-deg rees. The instrument therefore provides a means of measuring the direc tion and intensity of katabatic winds.