In the present study, we first examine the contribution of different, satellite-only or combined, global geopotential models in geoid computation employing the remove–compute–restore approach. For this reason, two test areas of about 100 km² each, one in northern and one in central Greece, were selected, and gravity measurements were conducted. These new gravity measurements were used along with the selected geopotential models to produce the reduced gravity field for the study areas. The classical and spectral residual terrain modeling effect is also removed to derive the residual gravity field. The latter is used for geoid computation using the 1D fast Fourier transform. The validation of the geoid models is carried out with gravity/GNSS/leveling measurements, which were conducted in two traverses located in the study areas. Special attention is given to the tidal approach, the geoid separation term as well as the coordinate reference system. Next, the northern study area is extended by incorporating gravity measurements obtained during the last five decades, and geoid models are recomputed. Lastly, using the geoid models computed, reference geopotential values are computed for both areas. From the results achieved for both study areas, the combined model XGM2019 provides the best overall statistical results with differences of 0.065 m and 0.036 m in terms of root mean square error. The incorporation of not recent data into the solutions leads to a degradation in accuracy by about 1.2 cm in terms of standard deviation. Lastly, the computed reference geopotential values present discrepancies between the two study areas, revealing network inconsistencies as well as the dependency on the geopotential model used for the geoid computations.

Recent Digital Surface, Elevation, and Bathymetric Models (DSM/DEM/DBM) aim to provide high-resolution and accurate height and depth information needed for a variety of surveying, geodetic, geophysical, and other applications. In this study, first we aim to validate in two test areas some of the most used models, i.e., ASTER GDEM; AW3D30 DSM; Copernicus DEM; EU-DEM; GEBCO 2020; NASADEM HGT; SRTM15+ and SRTM Global, using GNSS; spirit leveling; and gravity measurements. The validation is performed along two traverses of 14.5 and 12.0 km each in Northern and Central Greece, respectively. Since these models are based on geoid heights obtained from global geopotential models, we also investigate their influence on the validation results. Next, we carry out comparisons between GEBCO 2020, SRTM15+, and the Greek Seas DTM, with depths derived from in situ coastal measurements in six different areas in Northern Greece. From the analysis, we conclude that the heights obtained from the Copernicus DEM provide the best overall results in terms of mean value and standard deviation while also showing consistent results in the two test areas. Similarly, the Greek Seas DTM shows better consistency with the measured depths in the coastal test areas.

In the frame of the ModernGravNet project, a new experimental gravimetric quasi-geoid model for the broader Greek region has been developed. The computations were based on the remove-compute-restore approach, 1D spherical fast Fourier transform method with the Wong-Gore modification, XGM2019 as the reference geopotential model, and residual terrain modeling (RTM) scheme. The model’s evaluation was conducted using GNSS/leveling data across the Greek mainland, taking into account the geoid separation term. Furthermore, a velocity field model, derived from 16 years of continuous observations at 227 GNSS permanent stations in Greece and the adjacent areas, was incorporated into the evaluation process to assess temporal vertical changes. This model reflects the dynamic geometrical properties associated with the crust’s geophysical processes. As the gravimetric geoid was computed using gravity data from various time periods and the leveling data refer to an adjustment carried out four decades ago, the velocity field has been utilized to examine temporal changes in the GNSS/leveling data relative to the gravimetric geoid heights, aiming for more precise comparisons. The results obtained show an improvement in the comparisons up to 3 cm in terms of standard deviation. The study highlights the importance of adopting a dynamic geoid model and emphasizes the need for its thorough evaluation.