An accumulation map for the Greenland dry‐snow facies derived from spaceborne radar

Abstract

An important component of ice sheet mass balance calculations is the snow accumulation rate, traditionally determined across the ice sheet from interpolated ice core data. We derive an accumulation rate map within the Greenland dry‐snow facies, using C‐band radar backscatter and the mean annual temperature. Values for the backscatter were obtained from the ERS‐1 synthetic aperture radar mosaic acquired during September–November 1992. An empirical equation, based on elevation and latitude, is used to determine the mean annual temperature. We examine the influence of accumulation rate, and mean annual temperature on C‐band (5.3 GHz) radar backscatter, using a forward model, which incorporates snow metamorphosis and radar backscatter components. Our model is run over a range of accumulation and temperature conditions, consistent with the Greenland dry‐snow facies. On the basis of our modeled results, a look‐up table is generated, which uniquely maps the measured radar backscatter and mean annual temperature to accumulation rate. Our results compare favorably (15.4% average difference) with 124 in situ accumulation rate measurements falling within our study area. We attribute some of the differences to (1) unreliable in situ data points, which were based on a single year's accumulation and (2) a systematic underestimate of accumulation rate by our forward model in the low‐accumulation regions associated with the northern portion of our map. With questionable data points and those above 77°N removed, the average differences were less than 10.3%, as determined from 73 ice cores.