GRACE impact in geodesy and geophysics

R Biancale (1), M. Diament (2)
(1) GRGS-CNES Toulouse
(2) IPG Paris

After more than 7 years in orbit the GRACE satellites continue to successfully fulfil their mission in providing exceptional quality data of the Earth gravity field variations. Several groups among JPL, UTEX, GFZ, GRGS, GSFC… are currently delivering maps of these changes which provide us estimates of mass transfers at large scales (down to 400 km at best) over 10-day or monthly time spans.

The low Earth Satellite-to-Satellite Technique (SST) has then proved its ability to accurately monitor the geoid temporal variations. These are controlled by all mass transfers in the Earth system, the dominating ones being of hydrological origin. Beside the hydrology and glaciology sciences, geodesy and geophysics have benefited as well from the GRACE advances.

The improved static gravity field models of the Earth (by a factor 100 up to spherical harmonic degree 150 compared to former models) and slow temporal variations of low degree (< 50) coefficients allow to reduce now the modelling of gravitational Earth perturbations to millimetric level for low Earth orbiting satellites, leaving the non-gravitational perturbation errors preponderant. The recently launched GOCE mission will complete homogeneously the good resolution of models up to spherical harmonic degree 250, without to compete with GRACE for low degrees anyway. &In conjunction with other types of geodetic data GRACE has allowed as well to tackle two particular challenges in geophysics: discriminating between GIA signal and ice mass changes; studying the co-seismic mass displacement caused by large earthquakes such the Sumatra ones and associated post-seismic variations. This brought very new information on the mantle viscosity and the seismic cycle. &We propose to discuss these aspects and to outline as well desirable improvements and data product requirements for a follow-on mission.