Earth Planets Space, Vol. 52 (No. 11), pp. 1083-1089, 2000
Paulo de Oliveria Camargo1, João Francisco Galera Monico1, and Luiz Danilo Damasceno Ferreira2
1Department of Cartography, São Paulo State University, Rua Roberto Simonsen, 305 Centro Educacional, 19060-900 Presidente Prudente, SP, Brazil
2Department of Geomatic, Paraná Federal University, Centro Politécnico - Jardim das Américas, 81531-990 Curitiba, PR, Brazil
(Received January 7, 2000; Revised September 21, 2000; Accepted September 21, 2000)
Abstract: In the absence of the selective availability, which was turned off on May 1, 2000, the ionosphere can be the largest source of error in GPS positioning and navigation. Its effects on GPS observable cause a code delays and phase advances. The magnitude of this error is affected by the local time of the day, season, solar cycle, geographical location of the receiver and Earth's magnetic field. As it is well known, the ionosphere is the main drawback for high accuracy positioning, when using single frequency receivers, either for point positioning or relative positioning of medium and long baselines. The ionosphere effects were investigated in the determination of point positioning and relative positioning using single frequency data. A model represented by a Fourier series type was implemented and the parameters were estimated from data collected at the active stations of RBMC (Brazilian Network for Continuous Monitoring of GPS satellites). The data input were the pseudorange observables filtered by the carrier phase. Quality control was implemented in order to analyse the adjustment and to validate the significance of the estimated parameters. Experiments were carried out in the equatorial region, using data collected from dual frequency receivers. In order to validate the model, the estimated values were compared with "ground truth". For point and relative positioning of baselines of approximately 100 km, the values of the discrepancies indicated an error reduction better than 80% and 50% respectively, compared to the processing without the ionospheric model. These results give an indication that more research has to be done in order to provide support to the L1 GPS users in the Equatorial region.