The Ghanaian Gravimetric Geoid 2017 (GGG2017) covers the area between 4°N to 12°N and 4°W to 2°E. It is referred to the WGS84 reference ellipsoid and was computed using Heck and Grüninger’s modification of Stokes’ kernel in the framework of a remove-compute-restore approach. EGM2008 was used up to degree and order 222 to calculate the long-wavelength component of the geoid. A total of 499 surface gravity (from the Ghana Geological Survey Authority) and 29,249 marine gravity (from the Bureau Gravimétrique International) data were used to compute the GGG2017 model. Its validation was based on 11 GPS/trigonometric measurements, leading to the choice of the optimal maximum degree of EGM2008 and resulting in an overall accuracy of 45.7 cm. This means that the GGG2017 model can be used to replace second-order class II levelling, with an expected error of 6.8 mm/km for baselines ranging from 20 to 225 km.

The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.

The International Service for the Geoid (ISG) was founded in 1992 (as International Geoid Service - IGeS) and it is now an official service of the International Association of Geodesy (IAG), under the umbrella of the International Gravity Field Service (IGFS). The main activities of ISG consist in collecting, analysing and redistributing local and regional geoid models, as well as organizing international schools on the geoid determination (Reguzzoni et al., 2021).