Precise information of geoid undulations is essential for obtaining the orthometric heights from Global Positioning System (GPS) measurements over any region; apart from providing the information of subsurface density distribution. This paper presents computation of geoid undulations over a part of southern Indian region from terrestrial gravity and elevation data using remove–restore technique that involves spherical Fast Fourier Transform (FFT) to compute ‘Stokes’ coefficients. Computed geoid undulations are compared with geoid obtained from global geopotential models such as EGM2008 and EIGEN-GRACE02S and measured GPS-levelling records at 67 locations. Statistical analysis of comparison suggests that the computed gravimetric geoid model has a good match with the geoid determined from GPS-levelling with rms of 0.1 m whereas EGM2008 has 0.46 m. The differences of GPS-levelling with EGM2008 at majority of stations fall in the range of ±0.5 m, which indicates that EGM2008 may be used for orthometric height determination with an accuracy of <0.5 m in the south Indian region and offers a reasonably good transformation platform from ellipsoid to local datum. However, local determination of geoid is necessary for better accuracy of orthometric height from GPS. The gravimetric geoid calculated from the available gravity data shows considerable improvement to the global model and can be used to achieve orthometric height with an accuracy of 0.1 m.
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Acknowledgements
The authors would like tNGRI for his support and permission to publish this work. They are also thankful to C C Tscherning, for sharing GRAVSOFT and to Vagner Gonçalves for fruitful discussions. IFCPAR is acknowledged for the financial support provided through a project on Hydrology and Water Resources from Space over Indian region at NGRI.
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SRINIVAS, N., TIWARI, V.M., TARIAL, J.S. et al. Gravimetric geoid of a part of south India and its comparison with global geopotential models and GPS-levelling data. J Earth Syst Sci 121, 1025–1032 (2012). https://doi.org/10.1007/s12040-012-0205-7
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DOI: https://doi.org/10.1007/s12040-012-0205-7