Herceg, Matija

Knudsen, Per

Tscherning, Carl Christian

The main objective of this study is to study how gradients can be used to extract more short wavelength information of the gravity field and to use this enhancement to improve modelling of ocean circulation,i.e. MDT in regional area. This is done by development of a method for regional gravity field recovery by using GOCE gradients in addition to the global models. The Least Squares Collocation method requires the solution of as many linear equations as the number of data, so GOCE gradient data needs to be thinned prior to applying the method. To overcome this thinning, a Reduced Point Mass (RPM) method is developed as a part of this study. The RPM is based on the reduced point mass response.The results presented in this study are based on all available GOCE gradient data i

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Downloaded from orbit.dtu.dk on: Dec 21, 2017GOCE data for local geoid enhancementHerceg, Matija; Knudsen, Per; Tscherning, Carl ChristianPublication date:2012Document VersionPeer reviewed versionLink back to DTU OrbitCitation (APA):Herceg, M., Knudsen, P., & Tscherning, C. C. (2012). GOCE data for local geoid enhancement. Poster sessionpresented at GOCE Solid Earth Workshop , Enschede, Netherlands.zGOCE data for local geoid enhancementMatija Herceg1, Per Knudsen2, Carl Christian Tscherning11Universtity of Copenhagen, Denmark,  2DTU Space, National Space Institute, DenmarkGOCE Solid Earth workshop, 16-17 October 2012. Enschede, The Netherlandsmatija.herceg@geo.ku.dkAbstract ResultsMethodsThe main objective of this study is to study howgradients can be used to extract more short wavelengthinformation of the gravity field and to use thisenhancement to improve modelling of ocean circulation,i.e. MDT in regional area. This is done by developmentof a method for regional gravity field recovery by usingGOCE gradients in addition to the global models. TheLeast Squares Collocation method requires the solutionof as many linear equations as the number of data, soGOCE gradient data needs to be thinned prior toapplying the method. To overcome this thinning, aReduced Point Mass (RPM) method is developed as apart of this study. The RPM is based on the reducedpoint mass response.The results presented in this study are based on allavailable GOCE gradient data in the GOCINA region,i.e. 18 months of observations.Point-mass functions or multipole base-functions areharmonic functions, which may be used to represent the(anomalous) gravity potential T either globally or locally.The functions may be expressed by closed expressionsor as sums of Legendre series. In both cases at leastthe two first terms must be removed since they are notpresent in T. For local applications the effect of a globalgravity model is generally removed. Then, more termsneed to be removed or substituted by terms similar tothe error-degree variances. The Earth anomalousgravity field at one point is modeled by a set of basefunctions, each obtained as the anomalous gravitypotential from each point.2222222222111tancos1rVVrVrVrVrVrVrVrVExpressions for gravity gradientswhen using reduced point masses52223325232252)(311))cos(cossinsin(cos31)(sincos3ltrrlVllrVllrVqpqppqqqq2222222222222222111tancos1pppppppppppppprVVrVrttVttVrVrVrtVtrttVttVrV O. B. Andersen: The DTU10 Global Gravity field and Mean Sea Surface 2011. P. Knudsen: GOCINA: Geoid and Ocean Circulation in the North Atlantic. Technical report, 2005.N. Maximenko, P. Niiler, M. H. Rio, O. Melnichenko, L. Centurioni, D. Chambers, V. Zlotnicki, and B. Galperin:Mean dynamic topography of the ocean derived from satellite and drifting buoy data using three different techniques. J. Atmos. Oceanic Tech., 26(9):1910–1919, 2009.M. Herceg: GOCE data for Ocean Modelling, PhD thesis, 2012Even though GOCE data provides a better estimation of the MDT in the GOCINAregion than any previously obtained using only satellite observations, it could notbe concluded whether the regionally enhanced geoid model estimated usingGOCE gradients contribute to a further improvement of the determination of theMDT in the GOCINA area.GOCE Direct MDT current speeds reveal that all of the gross features of thegeneral circulation are clear. However, the MDT calculated in the GOCINA projectshows the smallest scale details, which makes it the best ocean circulationrepresentation in this region.Closed expressions for gravitygradients when using pointmassesGOCINA project MDT Maximenko MDT GOCE Direct enhanced MDTFigures are showing geoid height anomaly predicted by the LSC and the RPMmethods, when the EGM2008 up to harmonic degree and order 100 is subtracted.Power spectrum of the geoid height anomaly prediction when EGM2008 up to harmonic degree and order 100 is subtracted. The prediction is done by the LSC and the RPM methods with different datasetsGeoid [m] predicted usingthe LSC methodGeoid [m] predicted usingthe RPM method Difference between predicitonPower spectrum of the geoid height anomaly prediction when EGM2008 up to harmonic degree and order 240 is subtracted. The prediction is done by the LSC and the RPM methods with different datasetsPower spectrum of the difference between geoid height anomaly prediction (when EGM2008 up to harmonic degree and order 100 is subtracted) and EGM2008 based geoid height anomalyDTU10 current speed GOCE Dir enhanced current speed GOCINA MDT current speedDTU10 MDTMaximenko current speedFuture work:Use RPM method to supplementthe tools for investigation on howuncertainties in the conversionfrom P-wave velocity to densitypropagate into the gravity modeland the density model of theupper mantle.References

GOCE data for local geoid enhancement

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GOCE data for local geoid enhancement

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