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:: Volume 6, Issue 2 (9-2018) ::
jgit 2018, 6(2): 191-197 Back to browse issues page
Terrain effect in geoid determination by geopotential models
Soheil Hejrati *, Mehdi Goli
Azad University of Science and Research Ssahhrood
Abstract:   (1601 Views)
Topographic masses above the geoid are considered as a major obstacle in geoid determination by using Global Gravitational Models (GGMs). GGMs provide the possibility of the Earth's potential field modeling as the expansion of the external-type series of spherical harmonics. Applying the external expansion to obtain disturbing potential on the geoid within the topographic masses will cause a bias called ‘topographic bias’. This study deals with calculating geoidal height using Earth Gravitational Model 2008 (EGM08). In order to do so, two methods of Direct Analytical Continuation one and Rapp's Indirect one are utilized. The Analytical Continuation Approach is based on using EGM08 within the topographic masses and applying topographic bias. Alternatively, Rapp’s Approach is based on calculating height anomaly and its downward continuation on the geoid. The success of these two methods to geoid simulation on 490 GPS-Levelling stations in mountainous region of Colorado in the USA were evaluated. The results are an indicator of the fact that two methods are compatible with each other with centimetric accuracy compared to GPS-Levelling points. Also, it suggests an improvement in the relative and absolute accuracy of the geoidal height resulting from EGM08 about 60% in both methods. The numerical investigation revealed that taking advantage of height harmonic models instead of point actual height can bring a bias in the matter of a few centimeters on the geoid. Moreover, the absolute accuracy of Rapp's Approach is higher than Analytical Continuation Approach in geoid determination in comparison GPS-Levelling points.
Keywords: Analytical Continuation, Topographic bias, Geoid, Earth Gravitational Model
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Type of Study: Research | Subject: Geodesy
Received: 2017/10/24 | Accepted: 2018/01/31 | Published: 2018/09/22
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Hejrati S, Goli M. Terrain effect in geoid determination by geopotential models. jgit. 2018; 6 (2) :191-197
URL: http://jgit.kntu.ac.ir/article-1-596-en.html


Volume 6, Issue 2 (9-2018) Back to browse issues page
نشریه علمی-پژوهشی مهندسی فناوری اطلاعات مکانی Engineering Journal of Geospatial Information Technology
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