The Effect of Tropospheric Delay Modeling on the Determination of GPS-Derived Ellipsoidal Height in Permanent GNSS Networks using OPUS-Projects

M.A. Ugur, T. Richardson, D.A. Grejner-Brzezinska, C. Toth, and G.L. Mader

Abstract:	The National Spatial Reference System (NSRS) is the primary reference system used for land surveys and engineering applications, within the Continental United States. The Height Modernization Program, which has been designed and is being implemented by the National Geodetic Survey (NGS) is an ongoing operation focused on forming accurate, reliable heights using Global Navigation Satellite System (GNSS) technology in conjunction with traditional leveling, gravity, and modern remote sensing information. The traditional method for determining the elevation of vertical benchmarks is differential leveling; the disadvantages of this technique are high cost, time consumption, and nonsystematic errors (Roman & Weston, 2011). With the advance and expansion of space-based technology, GPS surveying has been used extensively for the production and propagation of survey control. In order for GPS-derived ellipsoidal heights to have any physical meaning in a surveying or engineering application, the ellipsoidal heights must be transformed to orthometric heights. The conversion of GPS ellipsoidal heights to orthometric heights typically involves measuring ellipsoidal heights, applying some form of geoid model and making an adjustment to fit the resulting orthometric heights to the existing vertical datum. NGS has been developing gravimetric geoid models to enable the determination of orthometric heights (H) since the 1990s. Since 1996, these gravimetric models have been combined with GPS and leveling information on known benchmarks to create a second type of models known as hybrid models. Hybrid models provide a practical and accurate transformation from GPS-derived ellipsoid heights to orthometric heights, called GPSderived orthometric heights (Milbert, 1991). The determination of GPS-derived ellipsoidal heights is one of the most critical components in the implementation of a precise hybrid geoid model, which, among others, are also subject to potentially significant error sources in GPS. These error sources reduce the accuracy of GPS-derived coordinates and ellipsoidal heights. The height component is primarily affected by inherent geometric weakness of GPS, that is, observing signals only above the horizon of the user, and by un-modeled part of a tropospheric delay. Some recent studies have shown that tropospheric delay is one of the most challenging and essential error sources in space based geodetic applications; especially in the determination of ellipsoidal height and the terrestrial reference frame (Mendes, 1999). This paper focuses on the techniques of achieving improvements in the accuracy of the GPS-derived ellipsoidal height, and addresses the effects of neutral atmospheric (tropospheric) delay and reference frame on ellipsoidal height. Most importantly, this paper demonstrates that these errors can be reduced, resulting in the improved accuracy of GPS-derived ellipsoidal heights, through the combination of the national and global permanent GNSS networks (Continuously Operating Reference Stations (CORS) and International GNSS Service (IGS)).
Published in:	Proceedings of the 2013 International Technical Meeting of The Institute of Navigation January 29 - 27, 2013 Catamaran Resort Hotel San Diego, California
Pages:	545 - 558
Cite this article:	Ugur, M.A., Richardson, T., Grejner-Brzezinska, D.A., Toth, C., Mader, G.L., "The Effect of Tropospheric Delay Modeling on the Determination of GPS-Derived Ellipsoidal Height in Permanent GNSS Networks using OPUS-Projects," Proceedings of the 2013 International Technical Meeting of The Institute of Navigation, San Diego, California, January 2013, pp. 545-558.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In