[G02-P] Poster

[G02-P-17] The GEOMED2 project: Multi-resolution aspects and aliasing in topographic effects for geoid and gravity determination

^○Riccardo Barzaghi¹, Georgios S. Vergos², Alberta Albertella¹, Daniela Carrion¹, Ilias N. Tziavos², Vassilios N. Grigoriadis², Dimitrios A. Natsiopoulos², Sean Bruinsma³, Lucia Seoane³, Franck Reinquin³, Marie-Françoise Lequentrec-Lalancette⁴, Corinne Salaun⁴, Pascal Bonnefond⁵, Per Knudsen⁶, Ole Andersen⁶, Mehmet Simav⁷, Hasan Yildiz⁷, Tomislav Basic⁸, Matej Varga⁸, Olga Bjelotomic⁸, Antonio J. Gil⁹ (1.Politecnico di Milano, Italy, 2.GravLab, Department of Geodesy and Surveying, Aristotle University of Thessaloniki, University Box 440, GR 54-124 Thessaloniki, Greece, 3.GET UMR 5563, Toulouse, France, 4.SHOM, Brest, France, 5.OCA/Géoazur, Sophia-Antipolis, France, 6.DTU Space, Kopenhagen, Denmark, 7.General Command of Mapping, Ankara, Turkey, 8.University of Zagreb, Zagreb, Croatia, 9.University of Jaén, Jaén, Spain)

One of the key aspects of the GEOMED2 project is the determination of a high-accuracy and high-resolution geoid model for the Mediterranean Sea along with the generation of gravity grids for various types of gravity anomalies like free-air, complete Bouguer, isostatic, etc. A crucial point in both geoid determination and gravity reductions, using the remove-compute-restore method, is the proper modelling of the topography/bathymetry effects on the available gravity anomalies. When estimating the high-frequency content of the gravity field spectrum the robustness and rigorousness of the determined topographic effects relies on both proper theoretical treatment and the soundness of the Digital Terrain and Bathymetry Model (DTM/DBM) used. Over land areas, the latest SRTM-based DTMs offer high-accuracy and high-resolution information on the topographic variations, in the sense that they properly manage to model the high-frequency contributions of the topographic masses. Over marine regions the situation is quite different, since the resolution of the DBMs available is not capable to remove the high-frequencies present in shipborne marine gravity data. Moreover, marine gravity data themselves do not have in many cases the necessary spatial resolution to rigorously model the high-frequencies depicted in the DBM. The main focus of the present work is on treating the aforementioned problems, i.e., to investigate and properly determine topographic effects over both land and marine areas to efficiently reduce land and marine gravity data towards geoid determination. Additionally, aliasing effects on the estimated topographic effects are investigated and the corresponding errors introduced in gravity anomalies and geoid heights are determined. Then, the DTM/DBM combination that provides the overall best results, in terms of the smoothness of the residual gravity anomalies, is outlined along with the final topographically corrected gravity anomalies and geoid indirect effects.