A Precise Geoid Model for Africa: AFRgeo2019
In the framework of the IAG African Geoid Project, an attempt towards a precise geoid model for Africa is presented in this investigation. The available gravity data set suffers from significantly large data gaps. These data gaps are filled using the EIGE
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Abstract
In the framework of the IAG African Geoid Project, an attempt towards a precise geoid model for Africa is presented in this investigation. The available gravity data set suffers from significantly large data gaps. These data gaps are filled using the EIGEN-6C4 model on a 150 150 grid prior to the gravity reduction scheme. The window remove-restore technique (Abd-Elmotaal and Kühtreiber, Phys Chem Earth Pt A 24(1):53–59, 1999; J Geod 77(1–2):77–85, 2003) has been used to generate reduced anomalies having a minimum variance to minimize the interpolation errors, especially at the large data gaps. The EIGEN6C4 global model, complete to degree and order 2190, has served as the reference model. The reduced anomalies are gridded on a 50 50 grid employing an un-equal weight leastsquares prediction technique. The reduced gravity anomalies are then used to compute their contribution to the geoid undulation employing Stokes’ integral with Meissl (Preparation for the numerical evaluation of second order Molodensky-type formulas. Ohio State University, Department of Geodetic Science and Surveying, Rep 163, 1971) modified kernel for better combination of the different wavelengths of the earth’s gravity field. Finally the restore step within the window remove-restore technique took place generating the full gravimetric geoid. In the last step, the computed geoid is fitted to the DIR_R5 GOCE satellite-only model by applying an offset and two tilt parameters. The DIR_R5 model is used because it turned out that it represents the best available global geopotential model approximating the African gravity field. A comparison between the geoid computed within the current investigation and the existing former geoid model AGP2003 (Merry et al., A window on the future of geodesy. International Association of Geodesy Symposia, vol 128, pp 374–379, 2005) for Africa has been carried out. Keywords
Africa Geoid determination Gravity field Gravity interpolation Window technique
H. A. Abd-Elmotaal () Civil Engineering Department, Faculty of Engineering, Minia University, Minia, Egypt e-mail: [email protected] N. Kühtreiber Institute of Geodesy, Graz University of Technology, Graz, Austria e-mail: [email protected] K. Seitz · B. Heck Geodetic Institute, Karlsruhe Institute of Technology, Karlsruhe, Germany e-mail: [email protected]; [email protected]
International Association of Geodesy Symposia, https://doi.org/10.1007/1345_2020_122, © The Author(s) 2020
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Introduction
The geoid, being the natural mathematical figure of the earth, serves as height reference surface for geodetic, geophysical and many engineering applications. It is directly connected with the theory of equipotential surfaces (Heiskanen and Moritz 1967; Hofmann-Wellenhof and Moritz 2006), and its determination needs sufficient coverage of observation data related to the earth’s gravity field, such as gravity
H. A. Abd-Elmotaal et al.
anomalies. In this investigation, a geoid model for Africa will be determined. The challen
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