Variations and errors estimates of TWS from GRACE for ...€¦ · Variations and errors estimates...
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Variations and errors estimates of TWS from GRACE for hydrological applications Liangjing Zhang, Henryk Dobslaw, Maik Thomas German Research Centre for Geosciences (GFZ) Department 1: Geodesy and Remote Sensing Section 1.3: Earth System Modelling [email protected]
Transcript of Variations and errors estimates of TWS from GRACE for ...€¦ · Variations and errors estimates...
Variations and errors estimates of TWS from GRACE for hydrological
applications
Liangjing Zhang, Henryk Dobslaw, Maik Thomas
German Research Centre for Geosciences (GFZ)
Department 1: Geodesy and Remote Sensing
Section 1.3: Earth System Modelling
GRACE
Motivation
Spherical harmonics Clm, Slm
Post-processing
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http://www.essc.psu.edu/
Terrestrial water storage (TWS)
Grids
(Rodell etc,2004)
Validation
Spherical harmonics Clm, Slm (d/o 90)
Level 2 RL05a from GFZ
GRACE Data
WGHM, LSDM, JSBACH, MPI-HM, GLDAS
Time span:2003.01—2012.12
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Post-processing method
GRACE Clm, Slm
Rescaled TWS estimates
-Degree 1 added -C20 replaced -Mean reduced -DDK2 Filtering
Filtered GRACE
TWS
Hydrological Model
Filtered Model TWS
Least square fit
Spectral domain Spatial domain
Rescaling factor k
Spectral/Spatial domain
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GLDAS
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Post-processing method -scaling factors
LSDM WGHM
JSBACH MPI-HM
Median
Contributions from each model to the median
Median: "middle" of a sorted list of numbers
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Post-processing method -scaling factors
Median of the rescaling factors
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Post-processing method -scaling factors
The variation coefficient of rescaling factors Correlation between filtered and original TWS (GLDAS)
Landerer&Swenson(2012)
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Post-processing method -scaling factors
Landerer&Swenson(2012)
The effect of rescaling
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Post-processing method -scaling factors
Error estimates
• Measurement error
Filtered TWS errors propagated from “calibrated errors” multiplied by scaling factors
• Leakage error
• Rescaling error
Multiplying by the RMS of the differences between each scaling factor and the median value
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Error estimates -gridded Measurement error Leakage error
Rescaling error Total error
Gridded error estimates serve as a start point for deriving basin-averaged TWS errors
The gridded TWS errors are spatially correlated
Method from Landerer&Swenson(2012) to consider covariance between different grids
d0 represent the de-correlation length scale in the Gaussian window
Error estimates
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Measurement error Leakage error
Rescaling error Total error
Error estimates –basin-averaged
Validation of hydrological models
GRACE Amplitude GRACE Phase
Mod
els
Am
plitu
de
Mod
els
Pha
se
Annual cycle
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Normalized RMS of TWS differences from GRACE and models
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LSDM
GLDAS WGHM
Validation of hydrological models
LSDM-ECMWF
LSDM with different forcings
LSDM-WFDEI
Conclusions • Globally gridded TWS variations and basin-scaled errors have
been obtained
• A median value of rescaling factors from five hydrological models make the rescaling more robust against particular weakness of a certain model
• Validation from GRACE TWS can be used to identify the deficiencies in the models which can help to improve the models (LSDM)
• Forcing data can have large effect on the model simulated TWS
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Thank you very much.
