Effects of the Ionosphere and Cycle-Slips in Long Baseline Dynamic Positioning

George Dedes and Angela Mallett

Abstract:	High accuracy positioning using GPS over long baselines requires On-The-Fly ambiguity resolution with simultaneous estimation of ionospheric effects. The GPS signals are dispersed by the ionosphere causing a group delay to pseudorange and a phase advance to carrier phase measurements. Proper modeling of ionospheric effects is very important for high accuracy positioning over long baselines for which the effects are significant. The Center for Mapping GPS positioning system uses a four measurement filter to estimate the widelane ambiguities and ionospheric effects. Positioning is performed using smoothed widelane pseudoranges. With this approach, horizontal positioning accuracies at the 0.05O.lOm level and vertical positioning accuracies at the 0.1 O-O. 15m level have been achieved over baselines of 60 km. These accuracies can be increased to the few cm-level when the ionosphere and the pseudorange and carrier phase multipath are properly modeled. Cycle-slip detection is very important since undetected cycle-slips will introduce systematic errors to the estimated positions. Cycle-slips are detected using the geomehy-free carrier phase observables together with the epoch-toepoch widelane estimates. The epoch-toepoch widelane estimates detect cycle-slips resulting from those combinations to which the geometry-free carrier phase observables are not sensitive.
Published in:	Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995) September 12 - 15, 1995 Palm Springs, CA
Pages:	1081 - 1090
Cite this article:	Dedes, George, Mallett, Angela, "Effects of the Ionosphere and Cycle-Slips in Long Baseline Dynamic Positioning," Proceedings of the 8th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1995), Palm Springs, CA, September 1995, pp. 1081-1090.
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