Geoid determination over Norway using global Earth gravity models

Due to increasing accuracy in measurements of the earth's gravity potential from satellite missions the goeid can be computed with higher resolution and accuracy than earlier. In the thesis the accuracy of geoid heights derived from global gravity models are investigated. GPS/leveling data are used to demonstrate the accuracy of global gravity models. In addition, national geoid models of Norway are compared at the same GPS/leveling stations. Geoidal heights from different global gravity models are computed over Norway. The geoid is computed in two different ways. In the rst method, geoidal heights are computed directly from geopotential coe cients and then corrected for topographical masses. Second method focuses on geoidal height computation through height anomaly. Prorper corrections are added. Accuracy of the models was investigated by comparing the geoidal heights from the models with geoidal heights found from 2329 GPS/leveling points distributed over whole Norway. It was also checked if the error was dependent of elevation. The only global gravity model that was close to the accuracy of the national geoid model is EGM2008 which has an accuracy of 6.9 centimeters while the national geoid models, NMA2013v22 has an accuracy of 5.6 centimeters. The accuracy increases with the degree and order of the model. It was also found that the indirect geoid determination had a small negative effect on the results.