Development of Real-time SNUDGPS via Ionospheric and Tropospheric Corrections

Changdon Kee and Doohee Yun

Abstract:	In conventional DGPS, ionospheric and tropospheric spatial decorrelation between reference station and user degrades positioning accuracy. As a result, coverage of one DGPS reference station is limited to 100-200km. This is also true for time transfer and Wide Area Differential GPS (WADGPS). When ionosphere activity is expected to be peak in year 2000, and also if the Selective Availability (SIA) is turned off in the near future, ionospheric time delay will be the biggest and the major error source to accuracy degradation. Last year, we developed a conceptual algorithm that can compensate differential ionospheric time delay, and we named it as SNUDGPS (Seoul National University DGPS). SNUDGPS is more accurate and economic than conventional DGPS because ionospheric spatial decor-relation effect can be eliminated by use of local area ionospheric time delay model and therefore the coverage of one SNUDGPS reference station can be extended to more than 500km. This means that we need smaller number of SNUDGPS reference stations than that of DGPS reference stations to cover the same area. Furthermore, SNUDGPS can be implemented by adding only two types of messages to RTCM-SC 104 (one is for nine nominal model parameters and the other for six perturbation model parameters in local ionospheric moclel) without any hardware change if DGPS reference station is equipped with a dual-frequency receiver. This year, we introduce a new version of SNUDGPS, which includes differential tropospheric error correction compensation at SNUDGPS users. This modification also improves positioning performance. Also, we developed sequential real-time estimation algorithm to identify local ionospheric model parameters as well as L1/L2 inter-frequency biases for all GPS satellites, simultaneously. Data were collected at both SNU and Cheju island, of which baseline is 453km. The experimental results show that the accuracy performance of SNUDGPS is improved more than twice compared to DGPS and therefore the coverage of SNUDGPS is expected to be extended more than twice of DGPS.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	1411 - 1419
Cite this article:	Kee, Changdon, Yun, Doohee, "Development of Real-time SNUDGPS via Ionospheric and Tropospheric Corrections," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 1411-1419.
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