Evaluation of GRACE and ICESat Mass Change Estimates Over Antarctica
The goal of this study is to examine some of the many corrections and processing strategies that can have a significant influence on the ice mass change estimates computed from GRACE and ICESat mission data. These two missions, when combined, have the pot
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Evaluation of GRACE and ICESat Mass Change Estimates Over Antarctica B.C. Gunter, R.E.M. Riva, T. Urban, R. Harpold, B. Schutz, P. Nagel, and M. Helsen
Abstract The goal of this study is to examine some of the many corrections and processing strategies that can have a significant influence on the ice mass change estimates computed from GRACE and ICESat mission data. These two missions, when combined, have the potential to generate new insights into the mass balance and geophysical processes of regions such as Antarctica, where such quantities are currently not well understood. Key to this combination is the identification of the major sources of uncertainty in the data processing. For the ICESat data, this includes an analysis into the calculation of the campaign biases, assumptions regarding the firn density, and a comparison between height rates derived from crossover and repeat track analysis. For the GRACE data, the focus will be on the impact of various GIA models and other a priori input values (i.e., C20 , geocenter motion, etc.). Comparisons with the latest data releases for both missions will be presented for the 4 year period spanning from October 2003 to October 2007. Recommendations for future work will also be discussed.
75.1 Introduction The GRACE and ICESat missions have been collecting coincident data since 2003, providing valuable
B.C. Gunter () Delft Institute of Earth Observation and Space Systems (DEOS), Delft University of Technology, Delft 2629HS, The Netherlands e-mail: [email protected]
information into the mass and surface deformation changes of the Earth. The observations are particularly valuable for regions such as Antarctica, where the near-polar orbits of both satellites ensure a high density of measurements. For Antarctica, GRACE can directly observe mass changes at monthly time intervals, but the interpretation of the results is limited by the spatial resolution of the measurements (~500 km). The measurements from ICESat can also be converted to mass change estimates, with the advantage that the spatial resolution is much higher; however, as altimetry measurements, they are insensitive to subsurface mass changes. For example, a combination of accumulation and compaction can result in a zero net height change, even though a mass change may have occurred. Other studies (Gunter et al., 2009) have shown that while the linear mass change trends computed from GRACE and ICESat data have high spatial correlations (i.e., features identified from either mission tend to be in the same geographical location and with the same sign), the actual mass change estimates were significantly different between the two missions. Much of the differences can be attributed to the various assumptions and input models used during processing. For example, GRACE by itself cannot separate the mass change due to ice loss/gain from that caused by glacial isostatic adjustment (GIA). As a result, models of the Earth’s interior and of the long term global ice history must be used to remove the contribution of
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