High-degree geopotential model tailored to Egypt

Abstract

The quality of the reference geopotential model used in the framework of the removerestore technique greatly affects the accuracy of the computed geoid. None of the existing geopotential models fit the Egyptian gravity field to the desired extent. The aim of this investigation is to have a smoothed gravity field so that it is unbiased and has significantly reduced variance by using a high-degree tailored geopotential model. The window technique has been applied to get rid of the double consideration of the topographic-isostatic masses within the data window. The high-degree tailored reference model has been created by merging the available gravity anomalies in the area of investigation with the EGM96 global gravitational data set. The merged global field has been used to estimate the harmonic coefficients of the tailored reference model by FFT technique using an iteration process to enhance the accuracy of the obtained harmonic coefficients (Abd- Elmotaal, 2004). Three different tailored geopotential models have been created by maintaining the lower harmonics till degree 20, 36 and 72 to their values as of EGM96 model. The results show that the tailored geopotential models give better residual gravity anomalies. The variance has dropped to its one third.