Satellite observations of ice sheet accumulation rate

Accurate predictions of sea level rise over the coming century will require improved knowledge of the processes controlling accumulation upon the Antarctic ice sheet. The sparsity of accumulation rate observations, both spatially and temporally, has hindered the development of this understanding. The authors describe a new method to observe accumulation rates using satellite observations of the thermal microwave emission at 4.5 cm wavelength. At this wavelength, scattering by grains is unimportant: the emissivity is controlled by reflections brought about by density stratification within the firn. The method relies upon a link between accumulation rate, and two parameters which characterize the stratification (the standard deviation of density fluctuations, and the mean layer thickness). By also linking these two parameters to the polarization ratio observed by the Scanning Multichannel Microwave Radiometer, the capability to map accumulation rates from space is developed. The resulting map broadly agrees with previously published compilations of Antarctic field data, though the importance of topography in controlling accumulation rates is made clearer. Regions of discrepancy with existing field data are likely associated with spatial variations in the development of snow crusts which strongly affect the polarization.