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An Investigation of Different GPS Processing Strategies for Deformation Monitoring of Large Earthern Dams
A. Fouladi
Faculty of Geodesy and Geomatics, of GK.N.Toosi University of Technology,
Iran
Email: fooladi@alborz.kntu.ac.ir
Behzad Voosoghi
Assistant Professor
Faculty of Geodesy and Geomatics
K.N.Toosi university of Technology
Email: vosoghi@kntu.ac.ir
In order to implement GPS observations for dam deformation monitoring purposes, sub centimeter displacements must be achieved in all three components of points displacement vectors. These high level of accuracy must be attained to provide sufficient warning of impending danger. In this application, namely dam deformation monitoring, where unfavorable conditions exist for gathering convenient GPS observations , this requirement is particularly challenging to meet. This research determines what accuracy can be expected in an unfavorable GPS environment. GPS data, which have been collected in a large earthen dam, are analyzed using optimal software settings, determined from a nearly ideal scenario.The GAMIT scientific GPS post processing software and GLOBK adjustment software respectively, were selected for post processing and adjustment of the GPS observations. The adjustment computations were done in inner constraint mode and, finally, the displacement vectors were derived. To compare the flexibility, user friendliness and solution reliability of commercial and scientific GPS processing software, GNSS was selected as a software, as a commercial one and reprocessed and adjusted all the baselines again. In the second stage of analysis, minimum constraint adjustment was carried out and the reference point stability analysis has been done to identify any unstable reference points. Finally absolute displacements of the object points are calculated. This comparison showed results obtained are compatible but those of the commercial software are too optimistic. We can also declare that by means of precise GPS observations collected based on the special requirements and adapting suitable processing techniques, sub centimeter accuracy for displacement vectors at 95% of reliability can be achievable in this context.
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