An Earth Gravity Field Model Complete to Degree and Order 150 from GRACE: EIGEN-GRACE02S



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EIGEN-GRACE02S geoid heights

EIGEN-GRACE02S anomalies

A medium-wavelength gravity field model has been calculated from 110 days of GRACE tracking data, called EIGEN-GRACE02S. The solution has been derived solely from GRACE intersatellite observations and is independent from oceanic and continental surface gravity data which is of great importance for oceanographic applications, as for example the precise recovery of sea surface topography features from altimetry. This model that resolves the geoid with on accuracy of better than 1 mm at a resolution of 1000 km half-wavelength is about one order of magnitude more accurate than recent CHAMP derived global gravity models and more than two orders of magnitude more accurate than the latest pre-CHAMP satellite-only gravity models.

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EIGEN-CHAMP03S

EIGEN-GRACE02S

Gravity anomalies (mgal) derived from the EIGEN-CHAMP03S (left) and EIGEN-GRACE02S (right) models.

This progress in accuracy together with an increase in resolution are the result of the dedicated instrumentation of the twin GRACE satellites. The instrumentation allows for continuous GPS-GRACE high-low satellite-to-satellite tracking, on-board measurement of non-gravitational accelerations, precise attitude determination, and - being the most important component - the observation of the inter-satellite distance and its rate of change.

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Error and difference amplitudes as a function of spatial resolution in terms of geoid heights.

It is expected that upcoming GRACE gravity models, with improved processing methods and computational models, will further increase the gravity field model accuracy towards the mission baseline accuracy in order to be able to resolve reliably the tiny signals of climatologically and geophysically induced temporal field variations. These include seasonal and interannual variations in the ocean/atmosphere mass distribution (ocean bottom pressure), in large scale continental water storage as well as in the thickness of the Antarctic and Greenland ice shields.

Large scale continental water storage resulting from monthly GRACE solutions three months apart (in units of equiv. water column)

With the completion of the anticipated five years mission lifetime also secular gravitational signatures due to trends in the ice/water mass balance and due to post-glacial adjustment very likely will be recoverable from space. Also, high resolution global gravity field models from a combination of satellite tracking, altimeter and surface gravity data such as the EIGEN-CG01C model benefit from the accuracy improvements in the long- to medium-wavelength part of the gravitational spectrum allowing a more thorough interpretation of the gravity field for geodynamic processes in the Earth's mantle/lithosphere system.

EIGEN-GRACE02S has been published in the Journal of Geodynamics. It may be cited as:

Christoph Reigber, Roland Schmidt, Frank Flechtner, Rolf König, Ulrich Meyer, Karl-Hans Neumayer, Peter Schwintzer, Sheng Yuan Zhu (2005): An Earth gravity field model complete to degree and order 150 from GRACE: EIGEN-GRACE02S, Journal of Geodynamics 39(1),1-10
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Dec 23, 2004, webadmin A.Helm