Recent changes in the microwave scattering properties of the Antarctic icesheet

Time series, satellite microwave data are used to monitor and quantify chan ges in the scattering properties of the Antarctic ice sheet. Daily ERS scat terometer (EScat) and Special Sensor Microwave/Imager (SSM/I) image data, a cquired since 1992, are analyzed to understand the seasonal and interannual changes over the ice sheet. For regions of the ice sheet where azimuthal m odulation is negligible, seasonal cycles are observed in both the EScat (am plitude similar to 0.5 dB) and SSM/I data (amplitude similar to 10 K) These cycles are attributed to seasonal changes in surface temperature. Interann ual variability in the time series signatures appears to be associated with accumulation, There is also evidence to suggest that shifts in the wind di rection can alter the backscatter through azimuthal modulation. Over the pe riod 1992-97, large trends are observed in the EScat(< -0.3 dB yr(-1)) and SSM/I (>1 K yr(-1)) signatures over several regions in Antarctica. These ch anges typically occur over ice shelves and at the margins of the ice sheet where previous melt events have occurred, and where accumulation is relativ ely high (>300 mm yr(-1)). It is likely the large changes result from the s uccessive burial of an efficient scattering layer formed by refreezing afte r a melt event prior to 1992, There is also evidence to suggest that simila rly large changes can be observed in the interior of the ice sheet due to t he burial of depth hear layers. In order to monitor long term change in the properties of the Antarctic ice sheet, it is necessary to remove the seaso nal cycle from time series microwave data. Such anomaly data can then be us ed to understand the link between EScat and SSM/I with accumulation and win d shifts.