Different ways to handle topography in practical geoid determination |
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Affiliation: | 1. CSIR-National Physical Laboratory, New Delhi 110012, India;2. Academy of Scientific and Innovative Research (AcSIR), CSIR-National Physical Laboratory, New Delhi 110012, India;3. Condensed Matter-Low Dimensional Systems Laboratory, Indian Institute of Technology, Kanpur 208016, India;1. Department of Biosystems and Agricultural Engineering, Oklahoma State University, Stillwater, OK, USA;2. Department of Irrigation and Drainage, Faculty of Agricultural Engineering and Technology, University of Agriculture Faisalabad, Faisalabad, Pakistan;3. Climate, Energy and Water Resources Institute (CEWRI) of Pakistan Agricultural Research Council (PARC), Islamabad, Pakistan |
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Abstract: | In this paper two different methods of how to handle topography in geoid determination is investigated. First method employs the Residual Terrain Model (RTM) remove-restore technique and yields the quasigeoid, whereas the second method is the classical Helmert condensation method, yielding the geoid. Both methods were used with the Earth Gravity Model (1996) (EGM96) geopotential model as reference, and results are compared to precise Global Positioning System (GPS) levelling networks in Scandinavia, especially an accurate GPS data set from the very rugged Sognefjord region, where the topography was represented by either a detailed (100 m) or a coarse (1000 m) digital terrain model. The inclusion of bathymetry in the terrain model was also investigated.Even if two different methods were used, they produced almost identical results at the 5 cm level in the mountains, but small systematic differences exist. Results show the importance of comparing the right types of geoid (classical geoid or quasigeoid), since differences in residuals are significant. |
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