Validation of EGM - 08 using GPS and LEVELING in Addis Ababa
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Date
2019-06
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Addis Ababa University
Abstract
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.
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Keywords
EGM - 08, LEVELING, Addis Ababa, GPS