Geoid determination over Norway using global Earth gravity Models

Abstract

Due to increasing accuracy in measurements of the earth's gravity potential from satellitemissions the goeid can be computed with higher resolution and accuracy than earlier. In thethesis 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. Inaddition, 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 geoidis computed in two different ways. In the rst method, geoidal heights are computeddirectly from geopotential coe cients and then corrected for topographical masses. Secondmethod focuses on geoidal height computation through height anomaly. Prorper correctionsare added. Accuracy of the models was investigated by comparing the geoidal heights fromthe models with geoidal heights found from 2329 GPS/leveling points distributed overwhole 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 modelis 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 degreeand order of the model. It was also found that the indirect geoid determination had asmall negative effect on the results.