Objectives The determination of the orthometric height of Mount Qomolangma requires the prior calculation of geoid height, which is determinined by the quasi-geoid (height anomaly) and the height difference between the quasi-geoid and geoid.
Methods First, based on Molodensky principle and remove-restore technology, a 1.5'×1.5' gravity quasi-geoid model in Mount Qomolangma region can be established by using a terrain model, an earth gravity field model, and the fusion data of ground and airborne gravity. Then, system errors can be eliminated by correcting the gravity quasi-geoid model with GNSS-leveling points. The quasi-geoid based on the National Vertical Datum 1985 can be obtained. Finally, the height difference between the quasi-geoid and geoid can be calculated by using the remove-restore method by gravity at the summit of Mount Qomolangma.
Results The results show that the EIGEN-6C4 earth gravity field model performs best in the region of Mount Qomolangma compared to EGM2008 and XGM2019e_2159. The precision of the gravity geoid model is 7.8 cm based solely on the EIGEN-6C4 and ground gravity data, while it is 4.8 cm based on the EIGEN-6C4 and the fusion data of ground and airborne gravity. The accuracy of model is improved by approximately 40% than using ground gravity data only. At the summit of Mount Qomolangma, the height anomaly is 25.586 m, the height difference between the quasi-geoid and geoid is 1.216 m, and the geoid height is (26.802±0.06) m in the National Height Datum 1985.
Conclusions Airborne gravity can effectively provide data for the region where ground gravity data is sparse or non-existent. By incorporating airborne gravity, the density of gravity data at the summit of Mount Qomolangma has been greatly improved, leading to an increased accuracy of the quasi-geoid model. The availability of richer data, more accurate models, and more advanced calculation methods in 2020 resulted in more reliable results compared to the 2005 measurement.
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