Gravity field modeling on the basis of GRACE range-rate

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Gravity field modeling on the basis of GRACE range-rate combinations

Pavel DitmarXianglin LiuDelft Institute of Earth Observation and Space System(DEOS)

Wuhan’s Hotine-Marussi Symposium 2006

May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006

Xianglin LiuPhysical Space Geodesy (DEOS)

Contents ...

• Methodology

• Simulation

• Real data processing

• Future outlook



GRACE• Launched on March 17,

2002, at least 5 years’ lifetime.

• Two satellites flying one after the other at about 220km distance.

• Altitude 500km, near-polar.

• NASA and DLR, CSR, JPL and GFZ.

• GPS receiver and accelerometer.

• KBR measures range of each other. @GFZ/CSR/JPL/DLR



GRACE

• Orbit determination can be done independently to cm level, relatively to 1~4mm.

• Biased ranges: <10μm.

• Range-rate:<1μm/s

• Accelerometer:10^- 4 μm/s^2 within the bandwidth of 4×10^-2 to 5×10^-5 Hz.

@GFZ/CSR/JPL/DLR



Methodology – working frame

A

B

X

Z

Y

X – Line-Of-SightZ – Orthogonal to X in the

instantaneous “orbit” planeY – Orthogonal to X and Z



Methodology – equation of motion



Methodology – functional model

Range-rate combinations:

Special case:



Methodology – functional model

Functional model:

Least-square solution:

How to do data weighting ?



SimulationS1: State vectors from orbit integrator (one month data set with 5s sampling);

S2: range and range-rates from state vectors;

S3: different noise into orbits and range-rates;

S4: Observed and reference RRCs from noised orbits and range-rates;

S5: compute corrections to coefficients of reference model.



Simulation – frequency-dependent weighting



Simulation – noise in orbits or range-rates



• July 9, 2003-Oct 17, 2003, totally 101 days;

• Reduced-dynamic orbits of satellite A;

• Relative baseline positions;• 1s sampling non-

gravitational accelerations;• 5s sampling quaternion

data;• 5s sampling KBR range-

rates.• Geophysics phenomena

are considered

Real data processing



Results



Results







More works to be done

• Nuisance parameters for unmodelling errors in orbits;

• Three component bias and scale factors for accelerometer data;

• Various ocean tidal models to be considered;• More data to be processed for computation a more

accurate mean model;• Temporal signals to be extracted.



Conclusions

• A new functional model is proposed. • Simulation and real data precessing verify the

approach.• A proper frequency-dependent data weighting is a

must;• The resulting gravity field model is rather sensitive

to errors in baseline vectors.



• Questions ?

Documents

Gravity field modeling on the basis of GRACE range-rate