Geoid is the equipotential surface of earth’s gravity field, which partially coincides with the mean sea level. The external Earth’s gravity field is represented by Global Gravitational Model (GGM) which is consisted of globally and homogeneously distributed terrestrial and satellite gravity observations. GOCE is one of the satellite missions that have been used to determine the gravity field of the earth. It mainly represents the long wavelength components of the gravity field which can be evaluated externally by using terrestrial data such as GPS levelling. 17 GOCE models are evaluated against EGM2008 and 134 GPS levelling stations. The RMSE of the undulation differences (N (GOCE models) – N (GPS levelling)) are considered the usual method for measuring the accuracy of the models. Another technique is used for evaluation, using the successive differences of the observed undulations against their corresponding values from the GOCE models. In this study, different types of GOCE models with different degree and order are examined against observed undulations and EGM2008 at three different distances. The first distance between the points is about 5 km which is the approximate distance between every two successive data points. The second distance is about 9 km which corresponds with the EGM2008 resolution, and the third case is about 85 km every two successive data points which is the average resolution of the assessed GOCE models. Numerical results showed that some of GOCE models gave comparable results with EGM2008 especially at level of undulation differences. |
