Validation of a Tropospheric Voxel Tomography Model in a Regional GPS Network

N. A. Nicholson, V. A. Hoyle, S. Skone and M.E. Cannon

Abstract:	Global Positioning System (GPS) signals experience ranging errors due to propagation through the neutral atmosphere. These range delays consist of a hydrostatic component, dependent on air pressure and temperature, and a wet delay dependent on water vapor pressure and temperature. Range delays arising from the hydrostatic component can be computed with accuracies of a few millimeters using existing models, provided that surface barometric or meteorological data are available. By using a regional network of GPS reference stations, it is possible to recover estimates of the slant wet delay (SWD) to all satellites in view. SWD observations can then be used to model the vertical and horizontal structure of water vapor over a local area, using a tomographic approach. The University of Calgary has deployed a regional GPS network in Southern Alberta with station spacing in the range of 30-100 km. Continuous network observations are currently logged at each site and are streamed to a central processing facility at the University of Calgary in real-time. This network is used primarily for research related to real-time precise positioning applications. One element of this work is improved troposphere modeling within the network, and secondary applications focus on meteorological processes and weather predictions. For these purposes, precise meteorological instruments are co- located with a number of stations within the network. Variable weather conditions occur in the foothills of the Rockies near Calgary, and the Southern Alberta network allows great opportunities to assess detection and modeling of severe weather events using GPS. Severe prairie thunderstorms are a multi-million dollar problem in Southern Alberta, and the physical processes associated with precipitation patterns are not well understood. These events form predominantly over the foothills near Calgary and may be identified in observations of 4-D water vapor distributions. In this paper, a newly developed 4-D wet refractivity model is implemented and tested using the Southern Alberta regional network. A field campaign was conducted, in collaboration with the Meteorological Service of Canada, to derive an extensive set of truth data from radiosonde soundings. The truth data was derived during summer months in which severe weather events are observed. This paper presents the validation of a voxel tomography approach implemented for the Southern Alberta Network using radiosonde-derived truth wet-refractivity values.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	2386 - 2395
Cite this article:	Nicholson, N. A., Hoyle, V. A., Skone, S., Cannon, M.E., "Validation of a Tropospheric Voxel Tomography Model in a Regional GPS Network," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 2386-2395.
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