Assessment of Geoidal Undulation (N) Values Computed with Reference to Different Earth Gravity Models

Abstract

This research entails the determination of the variations in global geoid undulation with reference to different Earth Gravity Models (EGMs). Geoidal undulation values of 22 points selected within the study area were determined from GPS derived data on differential mode. The undulation values were computed with reference to three different earth gravity models (EGM84, EGM96 and EGM2008) which use geopotential coefficients and spherical harmonic analysis. The results obtained were plotted and the configuration of the local geoid was obtained with respect to each gravity model. It was observed that structural development in the school (study area) since its inception in 1981 has forced some significant changes in the mass distribution in the school and consequently changes in gravity values which in turn changes the undulation values (which depends on gravity) from point to point. It was also observed that there was correlation between the local geoid determined and the nature of the topography. Areas with higher ellipsoidal or orthometric heights experience greater separation between the geoid and the ellipsoid.