Seasonal and Interannual Trends in Antarctic Ice Sheet Microwave Data

Time-series microwave satellite observations are used to investigate seasonal and interannual changes in the surface characteristics of the Antarctic ice sheet. Enhanced-resolution Cband ERS-1/2 scatterometer (ESCAT) backscatter and DMSP SSMI brightness temperature images of Antarctica, acquired on a 3-day interval between 1992 and 1997, have been analysed. Both ESCAT and SSMI data show a clear seasonal cycle over all areas of the ice sheet. Using multi-layered radiative transfer models we demonstrate these cycles result primarily from thermal forcing. We also note significant interannual trends in both data sets. At the margins of the ice sheet, where melting is known to have occurred, backscatter and brightness temperature trends are typically less than -0.25 dB/year and greater than +1 K/year, respectively. It is likely these trends are linked to accumulation of new snow and successive burial of scatterers (formed during the last significant summer melt period). In the interior of the ice sheet, where no melting occurs, there is generally no significant trend in the backscatter and a slight negative trend in the brightness temperatures. However, there are large spatial variations which we believe is caused by the presence of depth hoar layers or higher accumulation rates.