Herceg, Matija

Knudsen, Per

Tscherning, Carl Christian

The objective of this study is to develop methodology to use GOCE gravity gradients for enhanced geoid modelling and ocean circulation modelling. In specific regions with a rough gravity field, the resolution of the geoid may be enhanced substantially if GOCE gradiometer data are used in addition of the GOCE spherical harmonic coefficient model (EGMs) since in such areas the GOCE gradients contain more information than the EGM itself. Hence, the use of gradients may lead to improve the resolution of e.g. the marine geoid which in turn will improve the estimation of the ocean circulation. This is tested using GOCE gravity gradient data, the GEOCOL program (GRAVSOFT) and Reduced Point Mass (RPM) program. Tests are carried out in the GOCINA region and in the Mediterranean basin. Furthermore, the effect of the decreasing height of the GOCE satellite on gravity gradients and associated MDT is investigated

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Downloaded from orbit.dtu.dk on: Dec 21, 2017Use of GOCE L2 Gravity Gradients for full resolution GeoidHerceg, Matija; Tscherning, Carl Christian; Knudsen, PerPublication date:2014Document VersionPeer reviewed versionLink back to DTU OrbitCitation (APA):Herceg, M., Tscherning, C. C., & Knudsen, P. (2014). Use of GOCE L2 Gravity Gradients for full resolutionGeoid. Poster session presented at 5th International GOCE User Workshop, Paris, France.Use of GOCE L2 Gravity Gradients for full resolution GeoidMatija Herceg1, Carl Christian Tscherning2, Per Knudsen3(1) University of Copenhagen, IGN, Denmark; (2) University of Copenhagen, NBI, Denmark; (3) DTU Space, Denmark Technical University, DenmarkAbstractThe objective of this study is to develop methodology to use GOCE gravity gradients for enhanced geoid modelling and ocean circulation modelling.In speciﬁc regions with a rough gravity ﬁeld, the resolution of the geoid may be enhanced substantially if GOCE gradiometer data are used in addition of the GOCE spherical harmonic coeﬃcient model (EGMs) since in such areas the GOCE gradients contain more information than the EGM itself. Hence, the use of gradients may lead to improve the resolution of e.g. the marine geoid which in turn will improve the estimation of the ocean circulation. This is tested using GOCE gravity gradient data, the GEOCOL program (GRAVSOFT) and Reduced Point Mass (RPM) program. Tests are carried out in the GOCINA region and in the Mediterranean basin.Furthermore, the eﬀect of the decreasing height of the GOCE satellite on gravity gradients and associated MDT is investigated.matija.herceg@ign.ku.dkReferences[1] P. Knudsen: GOCINA: Geoid and Ocean Circulation in the North Atlantic. Technical report, 2005.[2] Tscherning, C. C. (2013), Developments in the implementation and use of Least-Suares Collocation. IAG Proceedings 143,  IAG2013[3] Herceg, M. (2012), GOCE data for ocean modelling. PhD Thesis, Department of Geodesy, Technical University of Denmark, Copenhagen, Denmark[4] Andersen, O. B., The DTU10 Gravity ﬁeld and Mean sea surface  (2010) Second international symposium of the gravity ﬁeld of the Earth (IGFS2), Fairbanks, Alaska.[5] Pail, R., Bruinsma, S., Migliaccio, F., Foerste, C., Goiginger, H., Schuh, W.-D., H¨ k, E., Reguzzoni, M., Brockmann, J. M., Abrikosov, O., Vicherts, M., Fecher, T., Mayrhofer, R., Krasbutter, I., Sanso, F., Tschern- ing, C. C., 2011. First GOCE gravity ﬁeld models derived by three diferent approaches. Journal of Geodesy 85, 819-843.5th INTERNATIONAL GOCE USER WORKSHOP | 25-28 November 2014 | UNESCO, Paris, FranceDiscussionComparison of geoid predicted by using higher GOCE orbit (Nov/2009 to Jul/2012) and when orbit was reduced (Aug/2012 to Sep/2013) showed no additional information in lowering of the satellite. However, when both datasets are used (full GOCE Tzz dataset: Nov/2009 to Sep/2013), comparison shows improvement in the geoid determination using Tzz gradients in the spectral band from the sph. harm. degree 180 to 280.The surface geostrophic currents calculated from the GOCE Direct MDT current speeds reveal that all of the gross features of the general circulation in the region are clear. However, the MDT calculated in the GOCINA project shows the smallest scale details, which makes it the best ocean circulation representation in this region.MethodologyTo investigate if a higher accuracy could be obtained by the direct use of GOCE satellite gradients, prediction of geoid height data was done in two diﬀerent areas: GOCINA (North Atlantic) [1] and Mediterranean region. In both regions, local geoid height prediction was done using two methods, one of them being Least-Squares Collocation (LSC, [2]) and the other the Reduced Point Mass (RPM, [3]).The results presented in this study are based on all available GOCE gradient data (from November 2009 to September 2013), but computed for three diﬀerent data timeseries (Fig. 1):    - from November 2009 to July 2012       (nominal GOCE orbit)    - from August 2012 to September 2013       (lowered GOCE orbit)    - from November 2009 to September 2013 Jan, 2010 Jan, 2011 Jan, 2012 Jan, 2013 Jan, 2014225230235240245250255260265270GOCE orbitSatellite height [km]DateFigure 2a: Truncated Tzz (contribution up to sph d/o 100 is subtracted) in GOCINA region.Figure 2b: Truncated Tzz (contribution up to sph d/o 100 is subtracted) in Mediterranean region.Figure 5a: Gocina DTU10 MDT Figure 5b: Mediterranean DTU10 MDT0 45 90 135 180 225 270 315 36010−710−610−510−410−310−210−1100Harmonic degree (n)m2n2TimeWise r5 residual geoid (degree 100 and up)LSC prediction, Tzz (selected 0.1x0.2)RPM prediction0 45 90 135 180 225 270 315 36010−610−510−410−310−210−1100101Harmonic degree (n)m2n2TimeWise r5 residual geoid (degree 100 and up)LSC prediction, Tzz (selected 0.1x0.2)RPM prediction0 45 90 135 180 225 270 315 36010−710−610−510−410−310−210−1100Harmonic degree (n)m2n2GOCE direct 3 modelLSC prediction, Tzz (sel. 0.1x0.2) higher altitudeLSC prediction, Tzz (sel. 0.1x0.2) lower altitudeRPM prediction higher GOCE altitudeRPM prediction lower GOCE altitude0 45 90 135 180 225 270 315 36010−610−510−410−310−210−1100101Harmonic degree (n)m2n2GOCE direct 3 modelLSC prediction, Tzz (sel. 0.1x0.2) higher altitudeLSC prediction, Tzz (sel. 0.1x0.2) lower altitudeRPM prediction higher GOCE altitudeRPM prediction lower GOCE altitudeTo ensure that the contribution of the masses outside the test areas can be neglected, truncation of the long wavelength part of the gravity ﬁeld (up to degree and order 100) is performed (see Fig 2).Figure 1: GOCE satellite orbit heightFigure 6a: Gocina Tim5 enhanced geoid power spectrumFigure 6b: Mediterranean Tim5 enhanced geoid power spectrumGOCINA MediterraneanFigure 3a: Mediterranean power spectrum of predicted geoid height by separate datasets for lower/higher GOCE altitudeFigure 3a: Gocina power spectrum of predicted geoid height by separate datasets for lower/higher GOCE altitudeComparison of geoid predicted by using two datasets: when GOCE satellite was in 255km orbit (Nov/2009 to Jul/2012) and when orbit was reduced (Aug/2012 to Sep/2013) showed no additional information in lowering of the satellite. (see Fig 3a and 3b).Figure 9a: GOCINA project current speedFigure 8a: Gocina Tim5 enhanced current speed (2° ﬁlter)Figure 8b: Mediterranean Tim5 enhanced current speed (2° ﬁlter)Figure 7b: Mediterranean Tim5 enhanced MDT (2° ﬁlter)Figure 7a: Gocina Tim5 enhanced MDT (2° ﬁlter)The model for the ocean Mean Dynamic Topography (MDT) is computed by removing the computed geoid based on the GOCE Time-wise global geopotential model (release 5, Tim5), enhanced by GOCE Tzz gradients, from the DTU10 Mean Sea Surface (MSS) [4].Figure 9b: Mediterranean DTU10 current speed

Use of GOCE L2 Gravity Gradients for full resolution Geoid

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Use of GOCE L2 Gravity Gradients for full resolution Geoid

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