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A 3-year series of Earth’s gravity field derived from GRACE range

measurements

Xianglin Liu, Pavel Ditmar, Qile Zhao, Erna OudmanDelft Institute of Earth Observation and Space System (DEOS), TU DelftGNSS Research Center, Wuhan University

GRACE Science meeting, Potsdam, Germany, 15-17, Oct. 2007

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical Space Geodesy (DEOS)

Contents ...

• Functional model and data processing procedure• Comparison with other solutions and some

highlights• Conclusions and acknowledgements

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical Space Geodesy (DEOS)

Functional model

Range Combinations (RCs):

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical Space Geodesy (DEOS)

Required orbit accuracy

g

=> = 0.4 mm 0.5 mkm/s

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical Space Geodesy (DEOS)

Data processing -- general scheme

Orbit & reference ranges

Residual ranges

Residual gravity field

Background force models

Observed ranges

++

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical 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.

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical 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

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical Space Geodesy (DEOS)

DEOS GLDAS

JPL GFZ

CNES CSR

Sep. 03

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical Space Geodesy (DEOS)

Aug. 03

Sep. 03

Oct. 03

GLDAS

DEOS

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical Space Geodesy (DEOS)

Apr. 04

May 04

Jun. 04

DEOS GLDAS

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical Space Geodesy (DEOS)

500 km Gaussian smoothing

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical Space Geodesy (DEOS)

500 km Gaussian smoothing

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical Space Geodesy (DEOS)

Greenland ice meltingDifferences between Feb 2006 and Feb 2003Equivalent water layer thickness, 500 km Gaussian smoothing

Sumatra-Andama earthquake

Differences between mean models of 2005 and 2004Equivalent water layer thickness, 300 km Gaussian smoothing

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical Space Geodesy (DEOS)

Sept. 03

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical 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.

• .

Oct 15-17 2007, GRACE Science Meeting, Potsdam, Germany

Xianglin LiuPhysical 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.