Study of Effects of the Plasma Bubble on GBAS by a Three-Dimensional Ionospheric Delay Model

S. Saito, T. Yoshihara, N. Fujii

Abstract:	Spatial gradient of the ionospheric plasma density is one of the most serious error source of differential GPS systems. Since Japan is located at relatively low magnetic latitudes (from 41 down to 19 degrees magnetic latitude), effects of low latitude ionospheric phenomena, especially a plasma bubble which is a region of depleted plasma density must be taken into account with great care. A 3-D ionospheric delay model which take into account the effect of the plasma bubble has been developed based on the NeQuick ionospheric/plasmaspheric plasma density model and on knowledge on the plasma bubble obtained in more than 30 years history of its study. GBAS is simulated (without any monitors) with our ionospheric model to investigate the impact of the plasma bubble on GBAS. Simulations are conducted with various satellite geometry, various plasma bubble location, and different approach directions. The results show that a single plasma bubble can cause a positioning error in vertical more than 10 m and needs to be detected by ground or airborne monitors. It is found that the impact of the plasma bubble is more significant when it comes around the meridian of the reference station, and not significant when it is located far east or west of the reference station. This result can be obtained only with a 3-D model which takes the plasma bubble structure into account. However, plasma bubbles in the real world generally have complex shapes, and multiple plasma bubbles are often observed at the same time. Considering these facts, the impact of plasma bubbles at low elevations in the east or west should be evaluated more carefully with more complex-shaped plasma bubbles, for example, based on the observation by VHF backscatter radars or airglow imagers. Our simulation code is designed so that various simulation parameters are flexibly chosen, monitors can be easily implemented, multiple plasma bubbles can be considered. Complex-shaped plasma bubbles will also be tested. Our model can be utilized not only for GBAS but also for SBAS or other applications. Our model shows reasonable and promising performance in modeling the ionospheric delay with a plasma bubble. It is quite useful in studying effects of plasma bubbles on GBAS to implement it in low latitude region, although our model needs more improvements which are being in progress. We believe that this kind of simulating tools are very necessary to potential GBAS systems in low latitude regions.
Published in:	Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009) September 22 - 25, 2009 Savannah International Convention Center Savannah, GA
Pages:	1141 - 1148
Cite this article:	Saito, S., Yoshihara, T., Fujii, N., "Study of Effects of the Plasma Bubble on GBAS by a Three-Dimensional Ionospheric Delay Model," Proceedings of the 22nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2009), Savannah, GA, September 2009, pp. 1141-1148.
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