Abstract
The geodetic and geophysical applications of Earth Gravity Field parameters computed from Global Geopotential Models (GGMs) are quite on the increase despite the inherent commission and omission errors of these models. In view of this, this study focuses on refining and quantifying terrain-induced effects on Bouguer gravity anomalies computed directly from a total of seven recent GGMs. In the study, the Residual Terrain Model (RTM) technique was used to estimate the residual terrain effects that were added to the GGM-computed Bouguer gravity anomalies at the sixty test points in Enugu State, Nigeria. The computed residual terrain effects range from -24.6 to 37.5 mgal while the percentage of the omission errors of the GGMs based on their Root-Mean-Square (RMS) differences ranges from 7.8% to 44.7%. It can be concluded that GGM-refined Bouguer gravity anomalies are better in accuracy than the unrefined GGM-computed Bouguer gravity anomalies and hence there is need for accurate height information in the development of GGMs. We, therefore, recommend that refined Bouguer gravity anomalies obtained from HUST-Grace2016s, EIGEN-6C4 and GECO that gave best improvement amongst the seven GGMs under consideration should be used to supplement the available terrestrial Bouguer anomalies for geodetic and geophysical applications within the study area.
Highlights
A Global Geopotential Models (GGMs) is a mathematical approximation to the external gravitational potential of an attracting body
The Residual Terrain Model (RTM) technique was used to estimate the residual terrain effects that were added to the GGM-computed Bouguer gravity anomalies at the sixty test points in Enugu State, Nigeria
The commission error is produced by the statistical errors of the fully normalized spherical harmonic coefficients while the omission error in spherical harmonic expansion comprises high-frequency gravity field signals that cannot be represented by a truncated spherical harmonic series expansion, that is, all gravity field features occurring at scales finer than the GGM’s spatial resolution [2] [3]
Summary
A GGM is a mathematical approximation to the external gravitational potential of an attracting body. It consists of a set of numerical values for certain parame-. GGMs are serving as good alternatives for modeling the gravity field of the earth especially in regions devoid of, or having inadequate terrestrial gravity data coverage. They are subject to omission and commission errors. Where the DEM is not very accurate in relation to the actual/observed terrain values, the effect is reflected in the accuracy of the computed parameter of earth gravity field being sought
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