1. Vermelding onderdeel organisatie A 3-year series of Earth’s gravity field derived from GRACE range measurements Xianglin Liu, Pavel Ditmar, Qile Zhao, Erna Oudman Delft Institute of Earth Observation and Space System (DEOS), TU Delft GNSS Research Center, Wuhan University GRACE Science meeting, Potsdam, Germany, 15-17, Oct. 2007

2. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Contents... Functional model and data processing procedure Comparison with other solutions and some highlights Conclusions and acknowledgements

3. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Functional model Range Combinations (RCs):

4. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Required orbit accuracy g => = 0.4 mm 0.5 mkm/s

5. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Data processing -- general scheme Orbit & reference ranges Residual ranges Residual gravity field Background force models Observed ranges + +

6. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Procedure of data processing -- background models (1)Static background model: EIGEN-GL04C up to degree 150. (2)Solid Earth tides and solid Earth pole tide: IERS-2003 convention. (3)Ocean tides: FES2004 model. 9 diurnal/semi-diurnal and 4 long- period constituents are considered up to degree 80. Ocean pole tide: Desai model up to degree 30 is considered. (4)Atmosphere and oceanic variability: AOD1B release 4 products up to degree 100 are used. (5)N-body perturbations: DE-405 ephemerides. (6)General relativistic perturbations. (7)Gravity field model correction obtained at the previous iteration.

7. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Residual RC : before 1st iteration Residual RC: before 2nd iteration Residual RC: before 3rd iteration Model (water layer): 1st iteration Model (water layer): 2nd iteration Sep. 03 Model (water layer): 3rd iteration

8. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) DEOS GLDAS JPLGFZ CNESCSR Sep. 03

9. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Aug. 03 Sep. 03 Oct. 03 GLDASDEOS

10. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Apr. 04 May 04 Jun. 04 DEOSGLDAS

11. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) 500 km Gaussian smoothing

12. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) 500 km Gaussian smoothing

13. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Greenland ice melting Differences between Feb 2006 and Feb 2003 Equivalent water layer thickness, 500 km Gaussian smoothing Sumatra-Andama earthquake Differences between mean models of 2005 and 2004 Equivalent water layer thickness, 300 km Gaussian smoothing

14. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Sept. 03

15. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Conclusions A new approach has been developed at DEOS to recover temporal gravity field variations from GRACE data. The approach is based on an iterative processing of inter- satellite ranges with a frequency-dependent data weighting. Three-year series (2003-205) of Earth's gravity field variations is produced. Years 2006-2007 will be processed in the near future. Computed models are in a good agreement with the GLDAS model of global hydrological variations. Further validation and public distribution is pending..

16. Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany Xianglin Liu Physical Space Geodesy (DEOS) Acknowledgements We are grateful to P. Visser, R. Kroes and T. Van Helleputte for providing us with GRACE orbits. Thanks also go to J. L. Chen, who provided us with the daily solutions of the GLDAS hydrological models in terms of spherical harmonic coefficients. We are also thankful to T. Mayer-Guerr for valuable discussions.