Development of Local Ionospheric Time Delay Model for Single-frequency DGPS Users

Changdon Kee and Doohee Yun

Abstract:	Ionospheric time delay is one of the main error sources for single-frequency DGPS applications, including time transfer and Wide Area Differential GPS (WADGPS). When ionosphere activity is peak in the year 2000 and also if the Selective Availability (SA) is turned off in near future, ionospheric time delay will be the biggest error source. [1] Currently, there are many attempts to develop real-time ionospheric time delay estimation techniques to reduce positioning error due to the ionospheric time delay. Klobuchar model is widely used for ionospheric time delay calculation for single-frequency users and uses flat surface at night time and cosine surface at daytime. [2] Since the Klobuchar model was developed for global ionosphere fit and it has singular points where their derivatives do not exist, it is not easy to use the Klobuchar model to estimate ionospheric time delay for single-frequency users. Therefore, there are needs to develop a new ionospheric time delay model which covers local region in view from one reference station with dual-frequency receiver, and send the parameters of the model to DGPS users. Since the coverage of one DGPS reference station is limited by ionosphere spatial decorrelation, this basic idea also can be used to extend the coverage of DGPS. We developed a new and practical ionospheric time delay model, which is simple to be used and does not have singular points and divergence problem in ionospheric time delay estimation. We also developed a new SNUDGPS (Seoul National University DGPS) which minimizes the effect of the ionosphere spatial decorrelation by sending ionosphere parameters to the DGPS users. Experimental results show that the mean of SNUDGPS three-dimensional positioning errors is reduced to at least half of DGPS and therefore the coverage of SNUDGPS is expected to be extended more than twice of DGPS.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	1113 - 1122
Cite this article:	Kee, Changdon, Yun, Doohee, "Development of Local Ionospheric Time Delay Model for Single-frequency DGPS Users," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 1113-1122.
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