Author : Hussein H. Karim, Imzahim A. Alwan and Basheer S. Jasim

Due to the importance of the subject and for the lack of such studies in Iraq, this research attempts to determine the accuracy of the geoid based on the available GPS and gravity data for the study area (Hilla, Iraq). To assess the geoid model accuracy, undulation measurements for terrestrial points in the area are compared with the undulation values resulted from the global model. Then, the standard deviations are determined which will be the indicator for the accuracy of the global model. The present analysis was carried on 21 gravity stations and 22 points observed by a GPS and level devices available in the study area. Topographic maps have been used to provide an accurate RTM for the study area instead of satellite data as they lack the required precision. After integrating the gravity data (Bouguer and Free air gravity data) with the global model EGM2008, the attained accuracies were ± 0.019 m for Bouguer data and ± 0.024 m for Free air data. Better results are achieved using Free air gravity data in calculation of the gravitational geoid as it is closer to the undulation accuracy extracted from the GPS/leveling method (± 0.034 m). Finally, as an evaluation, it can be stated from results that the computed geoid accuracy is acceptable and the present geoid model EGM2008 is considered as the optimal geoid so far for the study area. It is possible to produce a new geoid model by the method of interpolation using Free air gravity data but the scarcity of the gravity points of the study area and the lack of uniformly distributed points prevent us from producing a new geoid model.

Keywords: Geoid undulation, GPS, Bouguer and Free air Anomaly.

Article published in International Journal of Current Engineering and Technology, Vol.6, No.4 (Aug-2016)