Determination of Geoid Undulation by Astro-Geodetic Method
Publication: Journal of Surveying Engineering
Volume 142, Issue 3
Abstract
Civil engineering projects require the orthometric height of points (i.e., the height of points above geoid). Thus, to make use of the Global Navigation Satellite System (GNSS) in engineering surveying, geoid undulation (i.e., the separation between an ellipsoid and geoid surface) must be known. In this study, an attempt has been made to determine the geoid undulation using the astro-geodetic method. Observations were taken in a network of seven stations spread over 300 km2 around Dehra Dun, India. Astronomical observations of seven stars belonging to different constellations were taken with a theodolite having a least count of 1.0 s. Global positioning system (GPS) observations were taken using dual-frequency geodetic GPS receivers with a 0.1-mm-accurate digital level. Values of astro-geodetic geoid undulations (of stations) have been found close to that computed from field levelling. Further, the values have been compared with those obtained from global geoid models such as EIGEN6C3stat and EGM2008, and the astro-geodetic method was found to provide better accuracy than the global geoid models. Therefore, it can be concluded that the astro-geodetic method is the better choice for reducing GPS observation to orthometric height. In the future, the astro-geodetic method may be used to develop an accurate geoid model in general and for Indian topography in particular.
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Acknowledgments
The authors gratefully acknowledge the Survey of India and its personnel from the Geodetic & Research Branch for all the help and assistance they provided in carrying out the field and office work in this study.
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Published In
Journal of Surveying Engineering
Volume 142 • Issue 3 • August 2016
Copyright
© 2016 American Society of Civil Engineers.
History
Received: Jul 15, 2014
Accepted: Aug 6, 2015
Published online: Jan 4, 2016
Discussion open until: Jun 4, 2016
Published in print: Aug 1, 2016
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