Methods for geoid determination in regions with challenging data quality and coverage

The combination of satellite positioning techniques (e.g., GPS) and high-resolution geoid or quasi-geoid models provides an alternative to the expensive and time-consuming spirit leveling for the determination of physical heights. The reliability of the physical heights thus undergoes the same accuracy limitations of the (quasi-) geoid models. However, in many regions, especially developing or newly industrializing countries, there is no reliable regional gravity model, due to the low availability or quality of surface gravity data. This study tackles such challenges in a case study in the northwestern part of South America and provides the first up-to-date high-resolution Colombian quasi-geoid model.

This region is a challenging study area with coastlines on both the Pacific and the Atlantic Ocean and rugged topography with high elevation reaching more than 5,000 m. Available terrestrial and airborne data were collected during the last eight decades, which frequently contain systematic errors and biases and the corresponding metadata is missing. We develop approaches to validate and improve the quality of old gravity datasets. They are then combined with a global gravity model (GGM) and topography models, which play an important role in mountainous areas, within the remove-compute-restore (RCR) procedure. In the offshore area, satellite altimetry-derived gravity data are additionally incorporated, which are obtained from the latest release of the DTU (Technical University of Denmark) gravity anomaly grid, DTU21GRA.

The computed quasi-geoid model is thoroughly validated with independent GPS/leveling data. It delivers an STD of 15.76 cm in comparison to the GPS/leveling data, which is 36% smaller than that obtained from the latest South American quasi-geoid model QGEIOD2021 (24.51 cm). Five recent high-resolution GGMs, namely EGM2008, EIGEN6C4, GECO, SGG-UGM-1, and XGM2019 are also validated using the same GPS/leveling data. They deliver STD values of 28.09 cm, 21.10 cm, 20.39 cm, 20.93 cm, and 17.86 cm, respectively, which are averagely 38% larger than that of our computation.