Abstract
Time-variable gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) missions and satellite altimetry measurements from CryoSat-2 enable independent mass balance estimates of the Earth’s glaciers and ice sheets. Both approaches vary in terms of their retrieval principles and signal-to-noise characteristics. GRACE/GRACE-FO recovers the gravity disturbance caused by changes in the mass of the entire ice sheet with a spatial resolution of 300 to 400 km. In contrast, CryoSat-2measures travel times of a radar signal reflected close to the ice sheet surface, allowing changes of the surface topography to be determined with about 5 km spatial resolution. Here, we present a method to combine observations from the both sensors, taking into account the different signal and noise characteristics of each satellite observation that are dependent on the spatial wavelength. We include uncertainties introduced by the processing and corrections, such as the choice of the re-tracking algorithm and the snow/ice volume density model for CryoSat-2, or the filtering of correlated errors and the correction for glacial-isostatic adjustment (GIA) for GRACE. We apply our method to the Antarctic ice sheet and the time period 2011–2017, in which GRACE and CryoSat-2 were simultaneously operational, obtaining a total ice mass loss of 178 ± 23 Gt yr−1. We present a map of the rate of mass change with a spatial resolution of 40 km that is evaluable across all spatial scales, and more precise than estimates based on a single satellite mission.
Highlights
The Antarctic ice sheet is the largest reservoir of non-oceanic water mass
We show that our approach allows overcoming the limited resolution of the Gravity Recovery and Climate Experiment (GRACE) data, producing a field of ice mass trends that is evaluable across all spatial scales, and more precise than that recovered by a single sensor
Note that the data sets differ in the underlying GRACE data-CSR solutions for CSR RL05 M and ITSG-Grace2016 [58] for European Space Agency (ESA) Climate Change Initiative (CCI) Antarctica, and adopt different corrections of glacial-isostatic adjustment (GIA), both of which are part of our ensemble (ICE6G [32] computed by A et al [59] and IJ05r2 [30], respectively)
Summary
Projections estimate the ice sheet’s potential to raise sea levels by 15 m by the year 2500 for scenarios of unabated climate change [1] It is currently in a state of overall decline [2,3], but regional differences are very prominent. GRACE, on the other hand, measures mass change of the whole ice column It is not affected by the presence of different processes in the snow, firn, and ice column, GRACE has a significantly lower effective spatial resolution and needs to be corrected for all other mass change processes not related to the present-day ice mass change (for example caused by short-term mass variability in the atmosphere and the ocean). The method is applicable to other regions and components of the Earth system and may be useful to join GRACE/GRACE-FO data and additional measurements into new combined Level 4 data products
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