Calculation of elevation changing of Greenland's ice sheet using GLAS laser altimeter

The spaceborne laser altimeter has the advantages of divergence angle of milli arc magnitude and no penetration effect on ice surface, which are suitable for monitoring the icesheet changing of polar region. Using elevation data of GLAS laser altimeter, the ice sheet changing of the region above 2 000 m of Greenland was obtained and analyzed through the crossing and repeat pairs over the time span of March 2003 to March 2009. The novel method was developed and applied to calculate crossing pairs in the entire Greenland where the latitudinal span was very large. After coarse error elimination and time series analysis, a positive elevation change rate of 3.80 cm/year, and a standard deviation of 0.91 cm were obtained, and change trends from the crossing and repeat pairs were agreed. The number of repeat pairs was much larger than that of cross pairs, approximately 4-15 times, while its spatial distribution was very non-uniform. The conclusion is that on elevation change monitoring in Greenland's ice sheet, the crossing pairs is more fit for large zone, while the repeat ones suitable for small area.