Use of topography in the context of the GOCE satellite mission – some examples Moritz Rexer, Christian Hirt, Sten Claessens, Carla Braitenberg 5 th INTERNATIONAL GOCE USER WORKSHOP, Paris Session 4: “Solid Earth” 26 November 2014 Contact:

Content 1 Introduction : Gravity forward modelling 2 Evaluation of GOCE gravity fields using the topographic potential 3 Evaluation of topographic data using GOCE gravity fields 4 Global Bouguer gravity maps 5 Conclusions 5th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. 2 26/11/2014

Gravity forward modelling Applications Enhance observation-based gravity models (EGM2008, GGMplus) Validation of gravity models : fill spectral gap w.r.t. observed gravity Evaluation of gravity field models Evaluation of topographic models Computation of Bouguer anomalies Purpose 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. Model of the topography Gravity field model Gravity forward modelling

Technique 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. Solution to Newton’s law of gravitation Claessens S.J. & C.Hirt 2013, JGR

Models will soon be available via : Gravity forward modelling Topographic data sources 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. rock-equivalent topography rock density : 2670 kg/m³ 1 arcmin resolution Topographic data sources SRTM V4.1 CGIAR-CSI Bedmap2 GBT_V3 SRTM30_PLUS land topograph SRTM30_PLUS ocean bathym. SRTM30_PLUS inland bathym. Earth2014 RETdV_ELL_RET2014 uncompensated d/o 2190 spherical harmonics ellipsoidal approximation Gravity forward modelling

Evaluation of GOCE models using the Topopotential (I) 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. Method

Evaluation of GOCE models using the Topopotential (II) 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Hirt C. et al. Global Results DIR (1,2,3,4,5): GO_CONS_GCF_2_DIRx / TIM (1,2,3,4,5): GO_CONS_GCF_2_TIMx

Improvement of GOCE models (TIM models) with time in the spectral band: Evaluation of GOCE models 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. TIM1 using the Topopotential (III) Xinjiang / Northern Himalayas TIM3 TIM5

Evaluation of topographic data 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. Topography models and topographic potential models Topopotential model Input Topography model Topography sources Level of approxim ation Rock-equivalent topography modelling (RET) Reference dV_SPH_RET2011RET2011 SRTM (~2004), SS, Bedmap1, GLOBE, NSDIC Sphericalice-sheets, oceansHirt et al dV_SPH_RET2012 RET2012 SRTM v4.1, SRTM30plus, Bedmap1,GLOBE, NSDIC Spherical + major lakes Hirt & Kuhn 2012 dV_ELL_RET2012EllipsoidalClaessens & Hirt 2013 dV_ELL_RET2014RET2014 SRTM v4.1, SRTM30plus, Bedmap2, GBT_V3 Ellipsoidal + ice-shelves, water below ice This work dV_ETOPO1ETOPO1 SRTM30, GLOBE, GEBCO,RAMP,IBCAO EllipsoidalIce-sheets, oceansAmante & Eakins 2009 dV_KIT_RWIDTM2006 SRTM (~2004), GLOBE, Bedmap1, SS Ellipsoidal None – direct modelling Grombein et al using GOCE gravity fields (I) Method  RRs and CCs

Evaluation of topographic data 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. Global Results w.r.t. DIR5 using GOCE gravity fields (II)

Global Bouguer anomaly maps Technique 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. T GOCE TIM5dV_ELL_RET2014

Global Bouguer anomaly maps 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. GO_CONS_GCF_2_TIM5 gravity [mGal] d/o 10 km MinMax based on TIM-R5 and dV_ELL_RET2014

Global Bouguer anomaly maps 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. based on TIM-R5 and dV_ELL_RET2014 dV_ELL_RET2014 gravity [mGal] d/o 10 km MinMax

Global Bouguer anomaly maps 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. Bouguer gravity anomaly [mGal] d/o 10 km based on TIM-R5 and dV_ELL_RET2014 MinMax

Conclusion 1. Evaluation of GOCE models improvement of ESA GOCE models w.r.t short scale topographic signals Both R5 models similar up to degree 250 DIR-5 model shows best agreement with Topopotential beyond d/o 250 (highest RR and CC) 2. Evaluation of Topography Models / Topopotential Models GOCE enables independent & global evaluation of topographic data sets Improvement of Curtin University’s Earth RET models with each release 3. Global Bouguer maps from dV_RET_2014 at 80 km resolution (Earth2014 RET topography model) Spectral forward modelling: easy computation of Bouguer anomalies with ESA GOCE models GOCE USER TOOLBOX will use with dV_ELL_RET2014 for Bouguer computation 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al.

Acknowledgements 26/11/ th INTERNATIONAL GOCE USER WORKSHOP | Paris, France Use of Topography and GOCE, Rexer M. et al. With the support of the Technische Universität München – Institute for Advanced Study, funded by the German Excellence Initiative. We thank the Australian Research Council for funding via grant DP Thank you for your attention !