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Determination of Gravity Variations in Northern Europe from GRACE Jürgen Müller, Matthias Neumann-Redlin Institut für Erdmessung, University of Hannover, Germany (mueller@ife.uni-hannover.de)mueller@ife.uni-hannover.de Meeting of NKG Geodynamics WG, March 2006, AS, Norway
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Introduction GRACE Results Conclusions Contents
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Observation of GIA-Induced Effects Land uplift (1 cm / year) Observed by - GPS - GRACE - terrestrial gravimetry g = ± 2 Gal Scherneck et al., 2003
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Difference Between Terrestrial and GRACE Data Absolute gravimetry - point-wise observations - also local and regional effects - high-frequency signals GRACE - spatial solution (spherical harmonics) - long spatial wavelengths - more low-frequency temporal signals appropriate reductions required as well as temporal and spatial filtering
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GRACE Launch: March 2002 1cm-geoid with a spatial resolution of 200 km and temporal variations
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Spectral Characteristics of Temporal Effects GRACE error curves compared to various signal curves Spectra provided by GFZ Potsdam GRACE
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GRACE Monthly Solutions atmospheric and oceanic effects and tides already reduced using models
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GRACE: Temporal Gravity Changes (L/2 = 1500 km) Residual signal (hydrology) [units: Gal] Ocean, atmosphere Gravity differences of GRACE monthly solutions July – Sept. 2003 From CSR Solutions
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Analysis of Monthly GRACE Solutions secular and periodic variations Least-squares adjustment t = months ω1 = 2π/6 = semi-annual period ω2 = 2π/12 = annual period A, B, C, D, E, F = unknowns Amp_6 = Amp_12 = Phase_12 = Trend = B Errors 13 nm/s² for gravity anomalies (Gauss filter 800 or 500 km) 4 nm/s²/yr for secular variations 3 nm/s² for amplitudes
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Temporal Gravity Variations in Northern Europe Secular gravity variations (trend/year) as derived from GRACE data (Gauss filter 500 km) Bild Landhebung CSR (04/2002 – 03/2005)GFZ (02/2003 – 11/2005) -15 0 15 5 10 -5 -10 [μGal /year]
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JPLGFZ Secular variations [μGal/a] CSR Period: 02/2003 – 03/2005 (21 months) Gaussian Filter: 500 km Comparison of Latest Releases
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Different Gaussian Radii 500 km 600 km 700 km800 km GFZ (02/2003 – 11/2005)
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Periodic Gravity Variations in Northern Europe [μGal] [nm/s²] Amplitudes semi-annual annual 500 km 800 km
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annual phases Periodic Gravity Variations in Northern Europe (2) Months related to January
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Contribution of Hydrology amplitudes semi-annual GRACE WGHM Amplitudes annual [nm/s²] 0 10 20 0 10 20 8 0 5 2 8 0 5 2
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Contribution of Hydrology (2) GRACE Secular gravity variations per year WGHMGRACE-WGHM (period: April 2002 – June 2004) Both data show trend at the same location Signal is not in agreement with expected land uplift signal Further effects have to be considered -15 0 15 5 10 -5 -10 [nm/s² /year]
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Comparison with further Hydrological Models WGHMGLDASLaDWorld GRACE-WGHM GRACE-LaDWorldGRACE-GLDAS [nm/s² /year] -15 0 15 5 10 -5 -10 -15 0 15 5 10 -5 -10 Secular gravity variations per year
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Comparison with further Hydrological Models (2)
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Absolute Gravity Results - Example Vaasa Onsala
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Comparison with Absolute Gravity Data Absolute Gravity measurements with FG5-220 (IfE) Preliminary results, similar behaviour Further computations and investigations required VaasaOnsala
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Determination of land uplift signal from GRACE data Procedure - Filtering of monthly GRACE solutions - Errors of reduction models - Models of further mass variations - Spatial and temporal analyses of residuals - Comparison with uplift models and independent data - Extension of test area and generalisation of results New Funding Project in Germany
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Monthly solutions: January 2003 Different Representations of Gravity Gravity anomalies Gravity gradients [1/s²][m/s²]
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Difference: January 2004 - 2003 anomalies gradients Different Representations of Gravity (2) [1/s²] [m/s²] Difference: 0.2 mE
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Trend: Grace_Tzz (Gauss 500 km), [1/s 2 /year] Different Representations of Gravity (3) Difference: 0.06 mE/year
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Secular Mass Variations Siberia WGHM_500_23GRACE_500_32 Trend caused by hydrological effects [water column in cm/a]
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Determination of land uplift signal from GRACE data is very challenging – also from ground. Better GRACE models helpful Dedicated filtering and processing required Independent observations needed Inter-disciplinary cooperations indispensable Conclusions
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Trend caused by hydrological effects [water column in cm/a] Secular Mass Variations in Eurasia GRACE_500_32 WGHM_500_23
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GRACE_500_32 σ max ≈ 1,2 cm Annual amplitudes caused by hydrological effects [water column in cm/a] Annual Mass Variations Siberia
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