Evaluation of global gravity models from absolute gravity and vertical gravity gradient measurements in Turkey

A global gravity model (GGM) is a mathematical function describing the gravity field of the Earth. The assessment of GGMs involves identifying the best-fitting model to local gravity field for geodetic and geophysical applications. Thus, highly accurate independent datasets are required to obtain the appropriate model. In general, GPS/levelling data have been used for this purpose. If these measurements are not performed simultaneously, they may not be reliable due to vertical deformations especially in seismically active countries. Therefore, we used highly precise absolute and vertical gravity gradient measurements obtained by the Scientific and Technological Research Council of Turkey's (TUBITAK) National Metrology Institute and General Directorate of Mapping within the frame of Turkish Height System Modernization and Gravity Recovery Project over the period of 2016-2018 from Turkey to choose the best GGM for the whole of Turkey among the 19 latest tested satellite-only and combined GGMs (2004-2018). Our results showed that vertical gravity gradient measurements could also be used for the regional validation of GGMs as an independent in situ dataset. The GOCE based XGM2016 combined model and GO_CONS_GCF_2_TIM_ R5 satellite-based model were found to be the best-fitting models. The results also showed improvements over the widely used EGM2008 up to the spherical degree 270 for Turkey. The improvements of the GOCE models over the EGM2008 model are mostly seen in mountainous areas such as the Black sea, Aegean Sea, some parts of the Mediterranean, and South-eastern Anatolia regions with maximum improvements in the coastal areas of the Eastern Black Sea. The best-fitting GGMs to local gravity field identified with these measurements could be used for further geodetic and geophysical purposes in Turkey.