Summary
The ERS-1 wind scatterometer is an active microwave instrument operating at 5.3 GHz in the C-band with VV-polarisation. Measurements of the microwave backscatter coefficient of the surface are made at regularly spaced points within a 500 km wide swath along each orbit. The near polar configuration of the orbit combined with the orbital repeat cycle of the ERS-1 satellite provides total coverage of the Antarctic region each 3 days. The value of the backscatter coefficient depends on the incidence angle of the observation and on the look direction of the antenna. By removing the contributions to the backscatter of these two effects we derive normalised values of the backscatter coefficient and from these synthesise a sequence of composite radar images. Wind scatterometer data has been obtained from the ERS-1 satellite commencing in August 1991 in an almost continuous sequence up to March 1996. The composite images provide views of the whole region which are independent of solar illumination and weather conditions. We show a sequence of images to illustrate major events that occur within the seasonal sea ice zone: annual cycle of growth and decay of the sea ice cover; drift rate and direction of the sea ice and large icebergs; etc. Areas of significant sea ice production and the calving of large icebergs can also be identified. The value of the backscatter coefficient is sensitive to the wetness of the surface snow and presence of free surface water. Through this effect the spatial extent of significant surface melting at low elevations on the continent during the summer months can be clearly identified. Time series of the backscatter coefficient show that more subtle effects can be detected which are believed to be related to a change in moisture content of the near-surface snow. This can have a variety of causes, for instance increased solar radiation during the summer months, or an influx of warm air from lower latitudes.