We here determine the surface elevation and the winter snow accumulation rate along a profile in the percolation zone of the Greenland Ice Sheet from data collected with ESA's Airborne SAR/Interferometric Radar Altimeter System (ASIRAS) in spring 2004. The altimeter data show that in addition to a backscatter peak at the air-snow interface a dominant second peak occurs. This second peak appears due to the strong scattering properties of the last summer surface layer. A robust re-tracking algorithm was developed that enables the tracking of both interfaces. Utilizing this algorithm, the winter snow thickness is estimated to 1.50 1 0.13 m. This compares favorably with field measurements (1.43 1 0.04 m). The snow depth estimates in combination with snow-density measurements of 420 kg m-3 give a mean winter mass accumulation rate of 63 cm water equivalent (w.e.) and a spatial variation of 16 cm w.e. Furthermore a strong correlation is found between surface gradient and accumulation rate, with higher accumulation rate in flatter areas. The approach adopted here has significant potential for remote measurements of winter snow accumulation rate across ice sheets at larger spatial scales.