Assessment of the EGM2008 Gravity Field in Algeria Using Gravity and GPS/Levelling Data
The present work focuses on the evaluation of the EGM2008 geopotential model that was recently released by the NGA (National Geospatial-Intelligence Agency, US)/EGM-development team, in Algeria using the free air gravity anomalies supplied by BGI and GETE
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Assessment of the EGM2008 Gravity Field in Algeria Using Gravity and GPS/Levelling Data S.A. Benahmed Daho
Abstract The present work focuses on the evaluation of the EGM2008 geopotential model that was recently released by the NGA (National GeospatialIntelligence Agency, US)/EGM-development team, in Algeria using the free air gravity anomalies supplied by BGI and GETECH, the precise GPS data collected from the international TYRGEONET (TYRhenian GEOdynamical NETwork) and ALGEONET (ALGerian GEOdynamical NETwork) projects and the last Algerian local gravimetric geoid model. Additional comparisons of the terrestrial point data with the corresponding values obtained from other geopotential models were made. Five global geopotential models were used in this comparison: the Preliminary Earth Gravitational Model PGM2007A, the combined CHAMP and GRACE model EIGENCG01C, the combined GRACE and LAGEOS model EIGEN-GL04C, OSU91A and EGM96. The study shows that all tested models are an improvement over OSU91A geopotential model used in all previous Algerian geoid computations and that new released combined model (EGM2008) is relatively superior to other tested models in the Algerian region. According to our numerical results, the new EGM2008 model fits better the observed values used in this investigation. Its standard deviations fit with GPS/levelling data are 21.4 and 18.7 cm before and after fitting using four-parameters transformation model. We strongly recommend the use of this new model in the remove-restore technique for the computation of the improved geoid for Algeria. S.A. Benahmed Daho () Geodetic Laboratory, National Centre of Space Techniques, Arzew 31200, Algeria e-mail: [email protected]
61.1 Introduction The choice of the best geopotential model to reduce geodetic data is one of the critical steps in the geoid computation. Over the last 40 years, continuing improvements and refinements to the basic theory have been paralleled by the availability of more accurate and complete data and by improvements in the computational resources available for numerical modelling studies. These advances have led to the development of a sequence of global geopotential models of increasing spherical harmonic degree and order, and hence resolution. The most recent models are released from satellite gravity missions CHAMP and GRACE. In 2008, a new and revolutionary Earth Gravitational Model EGM2008 was realised by NGA. EGM2008 combines satellite (GRACE), marine (satellite-altimetryderived), and land gravity data to model the global gravity field with a geo-spatial resolution of 5 by 5 arcmin (Pavlis et al., 2008). It is complete to degree and order 2,159 and contains additional spherical harmonic coefficients up to degree 2,190. Its accuracy is largely dependent on the accuracy of GRACE, marine and land gravity data and their availability. The purpose of this work is to give a brief summary of the evaluation results for the EGM2008 Earth gravity model in Algeria using gravity and GPS/levelling data. In addition, the Preliminar
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