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Abstract:
The geometric method, which applies altimetry data for the estimation of changing ice volumes, makes it possible to estimate changes in ice volume with a very high resolution. However, the volume has to be converted to mass via a density model, which could have model uncertainties. The gravimetric method, which mainly focuses on the evaluation of GRACE time series, delivers a mass change map with a very rough resolution of only a few 100 km. Ice mass estimations, only based on gravity field time series, suffer from the so-called leakage effect. There are physically unreasonable assignments of negative mass changes to nearby oceanic areas. However, the mass changes are directly referred to changing gravity.
In order to estimate high-resolution ice mass balances for the Greenland ice sheet and its periphery, we combine gravity field time series and geometric information . We integrate geometric information in order to localize regions, where one can expect immense mass changes. By redistributing mass changes to those regions, we want to handle the mentioned leakage effect. To properly introduce the geometric information, we use a Tikhonov regularization with different parameters depending on the surface type: sea surface, land surface and ice-covered surface with geometric information.
Applying this method to GRACE data in the period 2002 to 2016, maps of mass rates for five year intervals are determined. We compute mass rates for the ice sheet and achieve similar results of ca. -100 Gt/a to -260 Gt/a as the Ice sheet Mass Balance Inter-comparison Exercise (IMBIE).
