A method of combining ICESat and GRACE satellite data to constrain Antarctic mass balance

Measurements from the Geoscience Laser Altimeter System (GLAS) aboard NASA' s ICESat satellite (2001 launch) will be used to estimate the secular chang e in Antarctic ice mass. We have simulated 5 years of GLAS data to infer th e likely accuracy of these GLAS mass balance estimates. We conclude that IC ESat will be able to determine the linear rate of change in Antarctic ice m ass occurring during those 5 years to an accuracy of similar to 7 mm/yr equ ivalent water thickness when averaged over the entire ice sheet. By further including the difference between the typical 5-year trend and the long-ter m (i.e., century-scale) trend, we estimate that GLAS should be able to prov ide the long-term trend in mass to an accuracy of about +/-9 mm/yr of equiv alent water thickness, corresponding to an accuracy for the Antarctic contr ibution to the century-scale global sea level rise of about +/-0.3 mm/yr. F or both cases the principal error sources are inadequate knowledge of postg lacial rebound and of complications caused by interannual and decadal varia tions in the accumulation rate. We also simulate 5 years of gravity measure ments from the NASA and Deutsches Zentrum fur Luft-und Raumfahrt (DLR) sate llite mission Gravity Recovery and Climate Experiment (GRACE)(2001 launch). We find that by combining GLAS and GRACE measurements, it should be possib le to slightly reduce the postglacial rebound error in the GLAS mass balanc e estimates. The improvement obtained by adding the gravity data would be s ubstantially greater for multiple, successive altimeter and gravity mission s.