Monitoring of Network Residual Ionosphere using ROT Index and its Application to the "Centimeter Level Augmentation Service"

Yuki Sato, Masakazu Miya, Norizumi Motooka, Seigo Fujita, Jun-ichi Takiguchi

Abstract:	An objective index of ionospheric disturbances, which has a strong mutual relation to a statistics of residual ionosphere in corrected GNSS measurement of ground users of a real-time centimeter-level positioning service, is investigated. Significant residual error of ionospheric correction remains even in a network-RTK service if an ionospheric disturbance with small spatial scale like medium-scale travelling ionospheric disturbances or plasma-bubble occurs, resulting in a slower time to fix of carrier phase ambiguity on the ground users. Some indices like I95L and IRIU are known as an index of a statistics of the residual ionosphere. In order to specify a performance of the service under a certain ionospheric condition, another objective index which indicates a situation where the statistics gets large is needed additionally. For a performance specification of “Centimeter-Level Augmentation Service” (CLAS) in Japanese Quasi-Zenith Satellite System (QZSS), we proposed to use an extension of Rate of TEC change Index (ROTI) known as an indicator of an irregular spatial structure of ionosphere as an objective index to define an exceptional condition concerning ionosphere in which the positioning accuracy obtained within a specified time is different from that in a regular ionospheric condition. ROTI is a standard deviation of rate of TEC change of a satellite in time observed at a single point. We found that once the definition of ROTI is extended to be a standard deviation of rate of TEC change of a satellite in time observed at multiple points, it shows a strong mutual relation to the standard deviation of the residual ionosphere in the corrected measurement of the satellite in the covered area. As an example, we evaluated the effectiveness of the exceptional condition with the threshold of 0.16 [TECU/min]. We found that 4.8 % of the two years data in CMAS corresponded to cases, and except for those cases, the percentage of cases that the statistics of the residual ionosphere was not subject to the distribution corresponding to the threshold was less than 5 %.
Published in:	Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014) September 8 - 12, 2014 Tampa Convention Center Tampa, Florida
Pages:	1065 - 1072
Cite this article:	Sato, Yuki, Miya, Masakazu, Motooka, Norizumi, Fujita, Seigo, Takiguchi, Jun-ichi, "Monitoring of Network Residual Ionosphere using ROT Index and its Application to the "Centimeter Level Augmentation Service"," Proceedings of the 27th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2014), Tampa, Florida, September 2014, pp. 1065-1072.
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