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Determination of Gravity Variations in Northern Europe from GRACE Jürgen Müller, Matthias Neumann-Redlin Institut für Erdmessung, University of Hannover,

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Presentation on theme: "Determination of Gravity Variations in Northern Europe from GRACE Jürgen Müller, Matthias Neumann-Redlin Institut für Erdmessung, University of Hannover,"— Presentation transcript:

1 Determination of Gravity Variations in Northern Europe from GRACE Jürgen Müller, Matthias Neumann-Redlin Institut für Erdmessung, University of Hannover, Germany Meeting of NKG Geodynamics WG, March 2006, AS, Norway

2 Introduction GRACE Results Conclusions Contents

3 Observation of GIA-Induced Effects Land uplift (1 cm / year) Observed by - GPS - GRACE - terrestrial gravimetry  g = ± 2  Gal Scherneck et al., 2003

4 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

5 GRACE Launch: March cm-geoid with a spatial resolution of 200 km and temporal variations

6 Spectral Characteristics of Temporal Effects GRACE error curves compared to various signal curves Spectra provided by GFZ Potsdam GRACE

7 GRACE Monthly Solutions atmospheric and oceanic effects and tides already reduced using models

8 GRACE: Temporal Gravity Changes (L/2 = 1500 km) Residual signal (hydrology) [units:  Gal] Ocean, atmosphere Gravity differences of GRACE monthly solutions July – Sept From CSR Solutions

9 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

10 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) [μGal /year]

11 JPLGFZ Secular variations [μGal/a] CSR Period: 02/2003 – 03/2005 (21 months) Gaussian Filter: 500 km Comparison of Latest Releases

12 Different Gaussian Radii 500 km 600 km 700 km800 km GFZ (02/2003 – 11/2005)

13 Periodic Gravity Variations in Northern Europe [μGal] [nm/s²] Amplitudes semi-annual annual 500 km 800 km

14 annual phases Periodic Gravity Variations in Northern Europe (2) Months related to January

15 Contribution of Hydrology amplitudes semi-annual GRACE WGHM Amplitudes annual [nm/s²]

16 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 [nm/s² /year]

17 Comparison with further Hydrological Models WGHMGLDASLaDWorld GRACE-WGHM GRACE-LaDWorldGRACE-GLDAS [nm/s² /year] Secular gravity variations per year

18 Comparison with further Hydrological Models (2)

19 Absolute Gravity Results - Example Vaasa Onsala

20 Comparison with Absolute Gravity Data Absolute Gravity measurements with FG5-220 (IfE) Preliminary results, similar behaviour Further computations and investigations required VaasaOnsala

21 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

22 Monthly solutions: January 2003 Different Representations of Gravity Gravity anomalies Gravity gradients [1/s²][m/s²]

23 Difference: January anomalies gradients Different Representations of Gravity (2) [1/s²] [m/s²] Difference: 0.2 mE

24 Trend: Grace_Tzz (Gauss 500 km), [1/s 2 /year] Different Representations of Gravity (3) Difference: 0.06 mE/year

25 Secular Mass Variations Siberia WGHM_500_23GRACE_500_32 Trend caused by hydrological effects [water column in cm/a]

26 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

27 Trend caused by hydrological effects [water column in cm/a] Secular Mass Variations in Eurasia GRACE_500_32 WGHM_500_23

28 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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