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Signal and Noise in GRACE observed surface mass variations. E.J.O. Schrama 1 , B. Wouters 1 , D.A. Lavallée 2 (1) TU Delft, The Netherlands, (2) University of New Castle, UK E-mail: e.j.o.schrama@tudelft.nl Related Publications: - PowerPoint PPT Presentation
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Signal and Noise in GRACE observed surface mass variations
E.J.O. Schrama1, B. Wouters1, D.A. Lavallée2
(1) TU Delft, The Netherlands, (2) University of New Castle, UK
E-mail: e.j.o.schrama@tudelft.nl
Related Publications:
Ernst J.O. Schrama, Bert Wouters and David A. Lavallée, Signal and Noise in Gravity Recovery and Climate Experiment (GRACE) observed surface mass variations, Vol. 112, B08407,
doi:10.1029/2006JB004882, 2007
Ernst J.O. Schrama and Pieter N.A.M. Visser (2007), Accuracy assessment of the monthly GRACE geoids based upon a simulation, Journal of Geodesy 81, 67-80, DOI 10.1007/s00190-006-0085-1
Kusche J, Schrama E.J.O., (2005) Mass redistribution from global GPS timeseries and GRACE gravity fields: inversion issues. JGR solid earth, Vol 110, B09409, doi:10.1029/2004JB003556.
Outline
Filter design + tuningA. GRACE CSR RL04 solutions are converted into surface mass gridsB. Empirical Orthogonal Functions are used to separate signal and noise
contained in the Gaussian smoothed surface mass gridsC. Result depends on an EOF approximation level “M” and a smoothing
radius “t”D. Optimal choice of “M” and “t” follows from observed deformations at
selected set of GPS stations within the IGS.
Test 1: Degree variance spectra A. Signal, EOF residual, GGM02C formal errors, B. Background model error tides and air pressure
Test 2: Residual analysis A. S2 tide and 180 day hydrology in EOF residualsB. Auto-covariance functions from EOF residuals are compared to
formal covariance functions based on a GSFC GRACE covariance matrix
6.25 deg, CSR RL04, 43 months
51.4%
9.5%
12.6%
EOF variances
EOF signal
EOF residual
0.85*GGM02C
FES2004-GOT00.2
NCEP-ECMWF
Equivalent water height degree spectrum at 6.25 degree smoothing
EOF signal
EOF residual 0.85*GGM02C
FES2004-GOT00.2
NCEP-ECMWF
Geoid height degree spectrum at 6.25 degree smoothing
Surface mass on 3 EOF modes and 6.25 degree smoothing radius
10 32 100 mm
GPS validation• IGS vertical loading within GRACE window• Accept only those IGS stations where rms of
difference relative to GRACE < 3 mm, and where the correlation is greater than 0.5
For the 59 remaining stations we find:
GSFC covariance matrix for July 2003 (Frank Lemoine)
Formal error for the EQWH map from GRACE covariance matrix
mm7.5 degree smoothing
Residual EQWH signal in EOFs 4 and up
CM6.25 degree smoothing
S2 (161 days)
180 days GRACE 180 days GLDAS
Residual signal in EOF 4 + up:
- S2 tide errors- Semi-annual hydrology signal
cm
Auto-Covariance functionsderived from EOFs 4 and up at 173E 0N
6.25 degree smoothing
W-E
S-N
Conclusions
• EOF filter method– 3 EOF modes and 6.25 degree smoothing– Synthetic EOF error = 0.85 * Formal error– Tide and atmosphere pressure errors are 3 to 5 times smaller
compared to formal GGM02C errors
• GPS validation– 3 modes 5.00 or 6.25 degree smoothing – 59 IGS stations calibration set
• Residual signal in EOFs 4 and up– S2 tide errors (161 days) identified– Semi-annual hydrology (180 days) recognized– Auto covariance still reveals North South striping that is not
fully explained by the formal covariance matrix
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