Assessment of the Greek Vertical Datum: A Case Study in Central Greece

In this study, the consistency of the Greek Vertical Datum (GVD) is examined, focusing on an area in central Greece and following similar efforts made in previous researches for the establishment of an International Height Reference System (IHRS). High precision GNSS measurements are available at trigonometric benchmarks located along the Gulf of Corinth, with benchmarks residing on both coasts along. First, the zero-level geopotential value (\( {W}_o^{LVD} \)) for the two areas, north and south coast, is determined, based on the classical Helmert theory using GNSS/leveling data and surface geopotential values derived from GOCE-based global geopotential models (GO-DIR-R5, GO-TIM-R5, GOCO05s and GECO) and EGM08. Then, the relative offset between the two areas is estimated while subsets of the computed benchmark values are also examined. Significant inconsistencies are detected that depend on the choice of benchmarks used in the computations. Moreover, a per benchmark analysis showed that the inconsistencies present a random spatial distribution and are attributed mainly to the orthometric height values of the benchmarks. Furthermore, the local \( {W}_o^{LVD} \) estimates are compared with previous results related to the GVD and the VD of the Greek islands and the corresponding value adopted by the IHRS. Finally, some remarks are drawn on the feasibility of the unification of the GVD with a global one.