| Summary: | Measurements of ice elevation from the Geoscience Laser Altimeter System (GLAS) aboard the Ice, Cloud, and Land Elevation Satellite can be combined with time-variable geoid measurements from the Gravity Recovery and Climate Experiment (GRACE) satellite mission to learn about ongoing changes in polar ice mass and viscoelastic rebound of the lithosphere under the ice sheet. We estimate the accuracy in recovering the spatially varying ice mass trend and postglacial rebound signals for Antarctica, from combining 5 years of simulated GRACE and GLAS data. We obtain root-mean square accuracies of 5.3 and 19.9 mm yr-1 for postglacial rebound and ice mass trend, respectively, when smoothed over 250 km scales. The largest source of error in the combined signals is the effect of the unknown time-variable accumulation on the density of the ice column. To estimate this contribution and so obtain better estimates of ice mass trend and postglacial rebound, we add Global Positioning System (GPS) measurements of vertical velocities as additional constraints. Using an empirical relation between the errors in postglacial rebound and ice mass trend that result from the unknown density variation within the ice column, we are able to solve for all three unknowns in the problem: ice mass trend, postglacial rebound, and the snow compaction trend. The addition of a plausible distribution of GPS measurements reduces the errors in estimates of postglacial rebound and ice mass trend to 3.4 and 15.9 mm yr-1, respectively.
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