![]() ![]() Thirdly, mass changes can be estimated from elevation change ( dH/dt) measurements using radar or laser altimetry. Secondly, variations in the gravity field can be used to estimate mass changes of the ice sheets using the GRACE satellites (Gravity Recovery and Climate Experiment). ![]() First, mass balance may be estimated from the difference between the net surface mass balance and ice flux through a gate. Three main approaches exist to estimate the mass balance of the Greenland and Antarctic ice sheets, each with their own errors and uncertainties. The proposed interpolation method will improve ice sheet mass balance reconstructions from existing and past satellite altimeter data sets, with generally poor sampling of outlet glaciers. Using this method increases volume loss estimates from Jakobshavn Isbræ by up to 20% compared to those obtained by OK. Spatiotemporal kriging smooths inter-annual variability and improves interpolation in periods with sparse data coverage and we conclude, therefore, that ST-KED produces the best results. When compared to ATM data, KED and ST-KED yield more realistic spatial patterns and higher thinning rates (over 20 m yr −1 as opposed to 7 m yr −1for OK). KED assumes a linear relationship between spatial gradients of velocity and dH/dt, which is confirmed for both negative (Pearson's correlation ρ < −0.85) and, to a lesser degree, positive ( ρ = 0.73) dH/dtvalues. The four methods are ordinary kriging (OK), kriging with external drift (KED), where the spatial pattern of surface velocity is used as a proxy for that of dH/dt, and their spatiotemporal equivalents (ST-OK and ST-KED). Here, four interpolation methods are compared and evaluated over Jakobshavn Isbræ, an outlet glacier for which widespread airborne validation data are available from NASA's Airborne Topographic Mapper (ATM). In those areas, straightforward interpolation of data is unlikely to reflect the true patterns of dH/dt. ![]() The largest dH/dtvalues occur over narrow, fast-flowing outlet glaciers, where data coverage of current satellite altimetry is poorest. Estimation of ice sheet mass balance from satellite altimetry requires interpolation of point-scale elevation change ( dH/dt) data over the area of interest. ![]()
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