Summary
Measurements of the microwave backscatter coefficient in the ku-band have been obtained over the Antarctic snow cover by the NSCAT wind scatterometer instrument on the ADEOS satellite from August 1996 to June 1997. The instrument has six antennas arranged with two directed forwards, one of them 45° to the left of the flight direction and the other 45°to the right, two directed aft 135° to the left and to the right, and two antennas directed approximately abeam, at 65° (i.e. forward) on the left and 115° (or aft) on the right. The swath width on each side is approximately 600 km, and the incidence angle ranges from a minimum of about 17° on the near side of each swath to a maximum of about 54° on the far-side. The spacing between adjacent ground tracks over the Antarctic continent is less than 25 km so that a given geographical point will fall within the instrument’s footprint on many neighbouring tracks. By accumulating observations of the backscatter coefficients measured within a small area from many orbits and all antennas a set of observations is obtained with many different incidence angles and multiple look directions. The value of the microwave backscatter coefficient of the snow surface depends on the surface roughness, crystal properties and structure within the snow cover, and moisture content. In the absence of any melting the physical properties are generally stable and hence the backscatter properties tend to be invariant with time so that observations accumulated over some finite time interval can be used to explore the angular variation in backscatter. The values of the backscatter coefficient of the snow cover exhibit a distinct angular anisotropy. This is apparent in the variation with both incidence angle and with antenna look direction. The backscatter coefficient for any point on the snow cover exhibits an approximately linear dependence on incidence angle. The azimuthal variation is described by a bi-sinusoidal function of the