Dramatic decrease in radar cross section over Greenland observed by the ERS-1 scatterometer between 1991 and 1995

Radar backscatter measurements obtained over Greenland by the ERS-1 scatterometer between August 1991 and November 1995 are investigated. The different snow and ice facies can be identified on NRCS maps by their different radar cross section. In the wet snow zones summer melting leads to a strong short-term decrease in NRCS of several dB in the months June to August (summer-dip). Here, a general trend of an increasing summer dip was observed from summer 1992 to summer 1995. In the Southwest part of Greenland for large areas of the percolation zone a significant trend of decreasing radar cross section of the order of 0.5 dB per year was observed, even when data of the summer-dip months were not considered. The largest gradients in radar backscatter are found at altitudes between 1500 m and 2500 m where the snow and ice cover persists during the entire year.