Abstract
Abstract The Gravity field and steady state Ocean Circulation Explorer (GOCE) maps variations in the gravity field by observing second order derivatives (gradients) of the Earth gravitational potential. Flying in the low altitude of 255 km and having a spatially dense data distribution of short wavelengths of the gravity field, GOCE may be used to enhance the time varying gravity signal coming fromthe GRACE satellites. The GOCE gradients may potentially be used for the determination of residual masses in local regions. This can be done using Least-Squares Collocation (LSC) or the Reduced Point Mass (RPM) method. In this study, different gravity field solutions are calculated by the use of RPM, LSC and GOCE gradients, respectively. Gravity field time series are created and presented for the six consecutive months of GOCE gradient observations, data being acquired between November 2009 and June 2010. Corresponding gravity anomaly results are used for the calculation of ice mass changes by the use of theRPMmethod. The results are then compared with the computed topographic effect of the ice by the use of a modified topographic correction and the Gravsoft TC program. The maximal gravity changes at the ground predicted from GOCE gradients are between 2 and 4 mGal for the period considered. The gravity anomaly estimation error arising from the GOCE gradient data using only Tzz with an associated error of 20 mE is 11 mGal. This analysis shows the potential of using GOCE data for observations of ice mass changes although the GOCE dataset is limited to only six months. We expect four years of GOCE gradient observations to be available by mid-2014. This will increase the accuracy and spatial resolution of the GOCE measurements, which may lead to an accuracy necessary for observing ice mass changes.
Highlights
The Gravity eld and steady state Ocean Circulation Explorer (GOCE) is the most advanced gravity space mission to date, and since 2009 it has mapped global variations in the gravity eld with remarkable detail and accuracy
The largest accelerations have been observed by the Helheim glacier, Kangerdlugssuaq and Jakobshavn Isbræ (JI) (Howat et al, 2011)
The aim of this study is to present the methodology for using GOCE gradients to possibly extract the signal that corresponds to the signal of change in JI ice mass
Summary
The Gravity eld and steady state Ocean Circulation Explorer (GOCE) is the most advanced gravity space mission to date, and since 2009 it has mapped global variations in the gravity eld with remarkable detail and accuracy. The success of the GOCE mission depends on adequate methodologies being developed for extracting the gravity eld from its observations and for combining the gravity eld with information from other sources In such a way, GOCE derived data has a possibility to add the insight needed in order to further our understanding of the physical processes occurring inside the Earth and on its surface. The GRACE satellites are 450 km above the Earth’s surface, which makes them relatively insensitive to shortscale terms in the gravity eld This means that the processing centers remove short-scale terms by truncating their solutions to a nite set of low-degree harmonics 60 for Release 5.0 (RL05) elds calculated by CSR (the Center for Space Research at the University of Texas) and 90 for solution calculated by GFZ (GeoForshungsZentrum in Potsdam), see Velicogna and Wahr (2013). In order to present GOCE capabilities of detecting ice mass change by using second order derivatives of gravitational potential observed by GOCE, the used time interval spans from November 2009 to June 2010
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