Andersen, Ole Baltazar

Herceg, Matija

Knudsen, Per

Tscherning, Carl Christian

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Dec 18, 2017Full Resolution Geoid from GOCE Gradients for Ocean ModelingHerceg, Matija; Knudsen, Per; Andersen, Ole Baltazar; Tscherning, Carl ChristianPublication date:2010Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Herceg, M., Knudsen, P., Andersen, O. B., & Tscherning, C. C. (2010). Full Resolution Geoid from GOCEGradients for Ocean Modeling. Poster session presented at European Geosciences Union General Assembly2010, Vienna, Austria.Full Resolution Geoid from GOCE Gradients for Ocean ModelingMatija Herceg1, Per Knudsen1, Ole Andersen1, Carl Christian Tscherning21DTU Space, National Space Institute, Department of Geodesy, Copenhagen, Denmark, 2NBI, University of Copenhagen, DenmarkIntroductionThe main objective of the study is to improve the methodology for combining GOCE gravity field models with satellite altimetry to derive optimal dynamic ocean topography models for oceanography. Since dynamic ocean topography determination is the difference between the sea surface and the geoid, the definition of both surfaces is of great significance. Here a method for geoid determination, using point mass method, is used for the regional determination of the gravity field that is not recovered by the planned global GOCE gravity model of spherical harmonic coeficients up to degree and order 200. Since no real GOCE data are available at this time, simulated gradient data are used taken from deliverables of GOCINA project.Poster number: EGU2010-10737ReferencesW.M. Telford, L.P. Geldart, R.E. Sheriff, D.A. Keys: Applied geophisics, 1985C. Antunes, R. Pail, J. Catalão: Point mass method applied to the regional gravimetric determination of the geoid, 2003R. Forsberg, C.C. Tscherning: GRAVSOFT, Geodetic Gravity Field Modelling Programs (overview manual),  2008P. Knudsen and The GOCINA team: Integration of Altimetry and GOCE geoid for Ocean ModelingEuropean Geosciences Union, General Assembly 2010, Vienna, Austria, 02 – 07 May 2010 mher@space.dtu.dkFig. 1.  GOCINA regionDiscussionThe preliminary results show that parts of the gravity field associated with harmonic degrees larger than degree 200 may be recovered using this method. Hence, the gravity gradients contain more valuable signal than will be recovered in the planned harmonic expansion up to degree 200, so this method led to improvements in the estimation of the geoid. The enhanced geoid may serve as a reference surface for satellite altimetry and provide improvements in the mean dynamic topography which in turn may be used to improve the modeling of the ocean circulation. Further studies on how to structure the point masses as dipoles within the earth to optimize the estimation are needed. Also, the error propagation should be studied rigorously, so that the contribution from the other components of the GOCE gradients can be studied properly.Point mass methodThe Earth anomalous gravity field, T, at point Q is modeled by the set of base functions, each obtained as the anomalous gravity potential from each point mass mi located at the position Pi on the surface of the ellipsoid with radius RM1 = 10 km and RM2 = 70 km smaller than the Earth mean radius RE . Using the least squares inverse method and formula for second order derivatives of gravitational potential, where masses are unknowns, grids of point masses on the two dierent level below the ellipsoid were created. At both depths point masses are located at regular grids having spacing of 0.25 degrees and 0.5 degrees in latitude and longitude respectively. Those grid spacing's were chosen to model the gravity field associated with harmonic degrees between 200 and 400 where the main improvements are expected to occur. The solution for the two burried mass grids were then used for geoid determination.ResultsTo produce residual gradient grid, the reference EGM96 gradients up to degree 200 were subtracted from the GOCINA gradients (Figure 2).  From the burried point mass grids the residual geoid heights were computed. Calculated geoid is shown in Figure 3.Compared with the Figure 2 the geoid heights show the same general pattern as the gradients. However, the geoid heights show more short wavelengths features than the gradients. The geoid solution was compared to the GOCINA geoid filtered using Gaussian filtering with a width of 1 degree to filter out short wavelength features of the geoid that may not be recovered from gradients at 258 km altitude. Fig. 3 Residual geoid calculated using point mass methodCompared to the result of the point mass solution, both geoid models show similar features with relatively high values southeast of Greenland as well as in the northern part of the region. The magnitude of the geoid based on the point mass solution is smaller and it appears to be smoother.Fig. 5 Diference between the two residual geoid solutionsFigure 5 shows the difference between the geoid based on the point masses and the GOCINA geoid described above.Fig. 2. Vertical gradients relative to the EGM96 model to harmonic degree 200   25222232222311)(iiiiiiiiiizszGmzsGmQPGmzQTz Fig. 4 Filtered GOCINA geoid relative to the EGM up to degree 200The magnitude of the unknown part of the simulated geoid is reduced from 38 cm to 19 cm. The short wavelength features are still present in the differences, but the main positive values southeast of Greenland and in the norther part of the region have been reduced. Also the negative values in the southeastern part of the region have been reduced. Hence, this preliminary test of the point mass method demonstrates its ability to recover parts of the gravity field that are not recovered by a spherical harmonic expansion truncated at harmonic degree and order 200.Min -1.52mMax 1.26mMean 0.00mSt. D. 1.210Min -0.05mMax 0.04mMean 0.00mSt. D. 0.025Min -2.46mMax 2.13mMean 0.00mSt. D. 0.380Min -0.84mMax 0.89mMean 0.00mSt. D. 0.190

Full Resolution Geoid from GOCE Gradients for Ocean Modeling

http://orbit.dtu.dk/ws/files/5757808/2010_EGU_Poster_herceg.pdf

Full Resolution Geoid from GOCE Gradients for Ocean Modeling

Abstract

Similar works

Full text

Available Versions

Online Research Database In Technology