Abstract
The regions around the world need to perform their results based on the local geoid. However, each region has different ground topography based on the amount of gravity in this region. Nowadays, the recent global Earth's gravity model of 2008 is successfully used for different purposes in geosciences research. This research presents an overview of the preliminary evaluation results of the new Earth Gravitation Model (EGM08) in the middle of Iraq. For completeness, the evaluation tests were also performed for EGM96 by examining 31 stations distributed over four Iraqi provinces. The national orthometric heights were compared with the GPS /leveling data obtained from these stations. This study illustrated that the GPS /leveling based on EGM08 data was better than that based on EGM96 data in terms of reducing the root mean square error (RMSE) of the differences between the orthometric heights and GPS/leveling data. The standard deviation (SD) values for the national orthometric heights and GPS heights were about 4 and 26cm, respectively. The results also show that there is a small difference in hight ranged (0.0013 - 0.1333 m) in Karbala, (0.0023 – 0.0062 m), in Najaf and (0.0173 – 0.0703 m), in Babylon. Due to the flat area, better results were obtained in Karbala and Najaf than Babylon. The EGM08 geoid method has shown to yield very close results to reality for various projects, thus its accuracy is acceptable.
Highlights
The Earth Gravitational Model (EGM08) is the modern version of a series of geopotential models developed under the management of the US National Geospatial-Intelligence Agency (NGA) [1,2,3,4]
Based on the known heights and computed ellipsoidal heights, geoid heights were computed at the 31 GNSS/leveling stations by rearranging equation (3) in [11, 9, 18, 19]. [20] explained local determination of geoid is necessary for better accuracy of the orthometric height from global positioning system (GPS)
The new Earth Gravitation Model must be examined in our region to evaluate the satisfaction level of using this EGM in Iraq
Summary
The Earth Gravitational Model (EGM08) is the modern version of a series of geopotential models developed under the management of the US National Geospatial-Intelligence Agency (NGA) [1,2,3,4]. Spherical Coeftients ( SHCs) that extend up to a degree of 2190 and an order of 2159 [5,6,7, 4] Since it has been released, EGM08 has become the standard geopotential model used for many applications, including geoid modeling. The local geoid calculation and determination can be computed from the combination of the leveling heights with the height from GPS [13, 12] This approach has been used widely throughout the world in engineering applications and projects, and it is satisfied within an area of about 1000 km2 [12]. The accuracy of the geoid model obtained from the geometric method is based on several factors, including the reference station of each of GPS along with the leveling stations and their homogeneity and distribution. An evaluation of the results of the EGM96 will be presented for comparison purposes
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