Implementation of a GPS Reference Network for Precise Real Time Positioning in Recife, Brazil

Stefan Willgalis, Gunter Seeber, Falko Menge, Claudia Pereira Krueger and Veronica M.C. Romao

Abstract:	Initiated through the SIRGAS project the Continuous Brazilian Monitoring Network (RBMC) with now 11 active GPS reference stations has been established by the Instituto Brasileiro de Geografia e Estatística (IBGE). The average spacing of the RBMC stations is about 500 - 1000 km and hence by far too large for precise real time applications. Local GPS reference networks are a means to provide cm-level positioning accuracy in real time for densely populated areas and important economic regions. Local, in this case, involves at least four reference stations and distances up to 100 km between them. Such a network was implemented for the urban area of Recife, in the Northeast of Brazil, and was operated for about three weeks during November 2000. Besides investigating the multi-station positioning approach under the particular ionospheric conditions in equatorial regions the network was used for several marine applications as well as geodetic control surveys, cadastral and GIS surveys, and car navigation. This project is part of the Bilateral Science and Technology Cooperation between the University of Hannover, Germany, and the two brazilian Universities Universidade Federal de Pernambuco (UFPE), Recife, and Universidade Federal do Paraná (UFPR), Curitiba. Distance dependent errors, introduced by ionosphere, troposphere and orbit, limit the applicability of standard RTK systems to a radius of less than 10 km from the base station. When setting up a network of permanent reference stations it is necessary to extend the station spacing as much as possible. Only a real time multi-station solution that models the distance dependent errors allows then the fast, reliable, and precise real time positioning. One approach to achieve this is the approximation of the ionospheric, tropospheric, and orbit residuals at all neighbouring reference stations by a plane or a polynomial of higher order. After parameterisation of the plane, the parameters are transmitted to the user. Using his approximate coordinates the user derives corrections from the parameters that will improve - compared to the standard RTCM based differential positioning - the ambiguity fixing process as well as the coordinate estimation process. The paper focuses on the real time multi-station positioning algorithm. The network architecture and implementational issues regarding hardware and software are also adressed. The high ionospheric activity in the equatorial region requires even for shorter distances multi-station solutions. Such results are without exception faster, more reliable, and more precise, but cannot compensate for severe tracking problems because of strong ionospheric scintillations.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	1071 - 1078
Cite this article:	Willgalis, Stefan, Seeber, Gunter, Menge, Falko, Krueger, Claudia Pereira, Romao, Veronica M.C., "Implementation of a GPS Reference Network for Precise Real Time Positioning in Recife, Brazil," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 1071-1078.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In