Regional assessment of high-degree combined global gravity field model for geoid modelling over Nigeria

Abstract Given the multitude of global gravity field model (GGMs) at our disposal, evaluating them against independent data is indispensable for delineating their quality and ascertaining their accuracy in Nigeria regions. In this study, we evaluated five combined GGMs (specifically SGG-UGM-2, XGM2019e_2159, GECO, EIGEN-6C4, and EGM2008) over Nigeria. Our evaluation is conducted using geoid undulations (mainly in FCT-Abuja) and free-air gravity anomalies (covering the whole country, Nigeria). The results showed that the differences between observed and GGMs implied geoid undulations at 20 GNSS/levelling points over FCT-Abuja (small area) revealed that XGM2019e_2159 fit better with standard deviation (SD) of 11.9 cm over the study area compared to other four evaluated combined GGMs. On the other hand, SD of the differences between observed and GGMs implied free-air gravity anomalies over Nigeria showed that XGM2019e_2159 performs slightly better than the other four evaluated combined GGMs with an SD of 7.04 mGal. These results further indicate a good prospect for the development of a precise gravimetric geoid model over Nigeria using XGM2019e_2159 model. However, more GNSS/levelling stations will be required for fittings of the gravimetric geoid model to the national vertical datum of Nigeria.