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Vermelding onderdeel organisatie
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
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
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
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
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
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
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
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
Methodology – equation of motion
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
Methodology – functional model
Range-rate combinations:
Special case:
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
Methodology – functional model
Functional model:
Least-square solution:
How to do data weighting ?
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
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.
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
Simulation – frequency-dependent weighting
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
Simulation – noise in orbits or range-rates
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
• 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
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
Results
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
Results
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
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.
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
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.
May 29 - June 2, Wuhan’s Hotine-Marussi Symposium 2006
Xianglin LiuPhysical Space Geodesy (DEOS)
• Questions ?
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