Evaluation of the GOCE-based gravity field models in Turkey

The recent GOCE-based global gravity field models are tested in Turkey and in two sub-regions, the Istanbul and Sakarya territories, by means of geoid undulations. Global gravity field model computed geoid undulations are compared with different sets of GPS/leveling-derived geoid undulations for different spherical harmonic degree expansions. High frequency components of the geoid undulations are estimated from EGM2008 and are removed from the GPS/leveling-derived geoid undulations. Therefore, model-based and GPS/leveling-derived geoid undulations are reduced to about the same gravity spectral band. The comparisons between the two geoid undulations are performed directly on the same benchmark points and also between the benchmark points by means of geoid slope differences. The comparison results suggest that GOCE-based as well as GRACE and GOCE combined satellite-only models provide better agreement with GPS/levelingderived geoid than EGM2008 by up to a few centimeters for medium wavelength gravity components. Based on the results obtained in this study, current and upcoming satellitebased gravity models are expected to improve the regional geoid, as well as the regional gravity prediction from such models. Turkey is currently discussing the options for height system modernization. The investigations performed in this study will be useful for the height modernization project of Turkey and will help the development of an accurate geoid model and improvement of the current vertical datum in the regions.