Geodesy and Geomatics

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Browsing Geodesy and Geomatics by Author "Alem, Seid"

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    Validation of EGM - 08 using GPS and LEVELING in Addis Ababa
    (Addis Ababa University, 2019-06) Alem, Seid; Tulu, Besha (PhD)
    The Global Positioning System (GPS) observations which is a component of the Global Navigation Satellite System (GNSS) is being referenced to the World Geodetic System 1984 (WGS84) ellipsoid with geographic coordinates defined in terms of latitude, longitude and ellipsoidal heights ( , ,ℎ). This prevalent situation makes it difficult to apply standard forward transformation equation for direct conversion of ellipsoidal heights (h) to a practical orthometric height (H) within Ethiopian local geodetic reference network. In order to overcome such a challenge, many researchers resort to various methods of determining the geoidal undulations for a local and national geodetic network and improving the recent New Earth Gravitational Model accuracies and its performances. This present study therefore seeks to validate the accuracy of the geoid heights derived from the Earth Gravitational Model 2008 (EGM08) in Addis Ababa. The estimated geoid heights obtained by the EGM08 model were compared with 9 geometrical geoid heights derived from co-located GPS and orthometric heights obtained by running first order geodetic leveling with a tie to the existing Blue Nile Bench Mark(1957- 1961). The methods applied include estimating the geoidal heights using the EGM08 model and a geometric method. The statistics of the differences between derived geoid heights by the geometric approach and corresponding geoid heights obtained from the Earth Gravity Model (EGM08) suggests an precedented accuracy (~2.27cm) of the geoid heights computed from EGM08.