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Full Resolution Geoid from GOCE Gradients for Ocean Modeling

Full Resolution Geoid from GOCE Gradients for Ocean Modeling. Matija Herceg & Per Knudsen Dep artment of Geodesy DTU Space. living planet symp o sium 28 June – 2 July, Bergen, Norway. Examples of Scientific Applications.

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Full Resolution Geoid from GOCE Gradients for Ocean Modeling

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  1. Full Resolution Geoid from GOCE Gradients for Ocean Modeling Matija Herceg & Per Knudsen Department of Geodesy DTU Space living planet symposium 28 June – 2 July, Bergen, Norway

  2. Examples of Scientific Applications Improved understanding of ocean circulation and energy distribution Gravity field map and improved global geoid models Global unification of height systems living planet symposium 28 June – 2 July, Bergen, Norway

  3. GOCE Products GOCE Level 2 products: • EGG_NOM_2_: Gravity Gradients in the Gradiometer Reference Frame (GRF), • EGG_TRF_2_: Gravity Gradients in Local North-Oriented reference Frame (LNOF), • SST_PSO_2_: Precise science orbits, • EGG_GOC_2_: Spherical harmonic series + derived quantities grids of geoid heights, gravity anomalies and deflections of the vertical are additionally included as well as geoid height errors, • EGG_GVC_2_: Variance-covariance matrix for the coefficients. GUT: The GOCE User Toolbox has been developed to facilitate the use of GOCE products for oceanographers and other communities such as Solid Earth physicists. living planet symposium 28 June – 2 July, Bergen, Norway

  4. GOCE Products GOCE Level 2 products: • EGG_NOM_2_: Gravity Gradients in GRF, • EGG_TRF_2_: Gravity Gradients in LNOF, • EGG_GOC_2_: Spherical harmonics series to degree and order 200 + grids. • GOCE gradients contain substantially more gravity relatedinformation than the spherical harmonic coefficient set, e.g.: • Knudsen and Tscherning (2005) found that the total geoid error (including omission errors) may reduce from about 30 cm to 15 cm when gradients are used regionally. living planet symposium 28 June – 2 July, Bergen, Norway

  5. Simulation Tscherning-Rapp model Simulated error degree variances living planet symposium 28 June – 2 July, Bergen, Norway

  6. Simulation living planet symposium 28 June – 2 July, Bergen, Norway

  7. Simulation living planet symposium 28 June – 2 July, Bergen, Norway

  8. This study • Apply methods for regional gravity field modelling to study potentialimprovements in the recovery of: • The gravity field, when using gravity gradients compared instead of the global spherical harmonics to degree and order 200: • Test signal transfer using a simple approximation – dipoles – to analyse resolution capability, • (Plan to) compare with optimal method (Least squares collocation). • The Mean Dynamic Topography: • Use and inter-compare with GOCINA test data. living planet symposium 28 June – 2 July, Bergen, Norway

  9. This study We will use synthetic data! - since no Level 2 data was available for this study. • Delta spikes • GOCINA test data: • Geoid • MDT living planet symposium 28 June – 2 July, Bergen, Norway

  10. The method We apply a simple gravity field approximation method to analyse the use of gravity gradients: The Dipole method: Point mass dipoles: Located on a regular grid: living planet symposium 28 June – 2 July, Bergen, Norway

  11. The method living planet symposium 28 June – 2 July, Bergen, Norway

  12. Test 1: Resolution capability Use a delta spike geoid signal of 0.5 m in a grid of zeros to Geoid > Gradients > Geoid Vzz: 16 cm living planet symposium 28 June – 2 July, Bergen, Norway

  13. Test 1: Resolution capability Vxx: 14 cm Vyy: 14 cm living planet symposium 28 June – 2 July, Bergen, Norway

  14. Test 1: Resolution capability Vxx: Vyy: living planet symposium 28 June – 2 July, Bergen, Norway

  15. Test 1: Resolution capability Vzz: Correlations and numerical instabilities cause problems inrecovering short wavelength parts of the gravity field. Success in recovering wavelengths down to about 70-80 km - corresponding to harmonic degree 500-600 roughly. living planet symposium 28 June – 2 July, Bergen, Norway

  16. Test 2: GOCINA MDT In the second test the improvements of the geoid and the MDT in the GOCINA region are studied: • As a first approximation the EGM96 to deg. 200 is used. • Subsequently the geoid is improved using simulated gradients (Vzz only) derived from the residual gravity field. • Preliminary results: • RMS values • (smoothed quantities) living planet symposium 28 June – 2 July, Bergen, Norway

  17. Test 2: GOCINA MDT Plots of geoid and MDT residuals: They are very similar. living planet symposium 28 June – 2 July, Bergen, Norway

  18. Results The results of the initial tests demonstrate that: GOCE gravity gradient data may improve the geoid above harmonic degree 200 up to about 500-600, The improved geoid improves the modelling of the MDT. Hence, the use of GOCE gradient for regional improvements in the modelling of the MDT will be important for regional ocean circulation modelling. Much more to do... With real data... living planet symposium 28 June – 2 July, Bergen, Norway

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