Investigation and Modeling of Effects of Ionospheric Plasma Bubbles on GBAS Availability and Its Mitigation by GPS/INS Integration

T. Fujiwara, T. Tsujii, T. Kubota

Abstract:	To contribute to the realization of the next-generation air transportation system, Japan Aerospace Exploration Agency (JAXA) is promoting the research and development project named DREAMS (Distributed and Revolutionary Efficient Air-safety Management System). Research and development of high precision and reliable navigation system is one of the most important targets of this project. In this paper, the impacts of the ionospheric plasma bubble on the GBAS availability are investigated and its mitigation techniques by GPS/INS integration are introduced. Though the impacts of ionospheric anomalies on GBAS integrity have been researched well so far, the impacts on GBAS availability have not been well investigated. Since the ionospheric plasma bubbles arise much more often than the Storm Enhanced Density (SED) in the regions at low magnetic latitude, its impacts on the availability should be investigated as well as the impacts on the integrity. Although GNSS has been widely used for many kinds of positioning/navigation/timing applications, its accuracy and reliability would not be sufficient under a harsh environment (e.g., ionospheric anomaly). For the safety-of-life applications, such as aircraft operations, to retain reliability in any condition is of great importance. Therefore, some kinds of augmentation systems are necessary for aircraft operations. While Satellite Based Augmentation System (SBAS) is one of such augmentation systems, Ground Based Augmentation System (GBAS) has been developed and evaluated as a unique solution for Category II/III precision approach. However, even with such augmentation systems, the availability might not be sufficient under harsh environments which are a severe ionospheric anomaly and intentional/unintentional interference. It is well known that the Storm Enhanced Density (SED) associated with a severe geomagnetic storm causes a large spatial gradient of the ionospheric delay. However, the effect of the plasma bubble has to be considered in the countries at relatively low magnetic latitude including Japan since it is a common phenomenon in such a region and often causes scintillation as well as spatial gradient. Therefore, the evaluation of GPS performance under the ionosphere plasma bubbles is an important task in order to introduce a new safety-of-life technology such as GBAS. The plasma bubble is a low-latitude and equatorial ionospheric phenomenon, which arises after sunset, moves eastward, and disappears before dawn. Since the electron density inside the bubble is extremely lower than that of the outside, the ionospheric delay may drop steeply. Since the steep change of the ionospheric delay may degrade the accuracy and reliability of GBAS, such signal is excluded by the Code Carrier Divergence (CCD) monitor. GNSS signal passing through the bubble may be fluctuated randomly as well and signal scintillation may be invoked. To assess the GBAS availability under anomalous ionosphere conditions with ionospheric plasma bubbles, a lot of Monte Carlo simulations had been conducted as previously reported. To improve the numerical simulation models, actual GNSS observations have been collected at the ground station in a low magnetic latitude region since last year. Flight trial campaigns collecting dynamic GNSS data have already been conducted twice since last year and additional campaigns are planned semi-annually during these high solar activity years. The latest products resulting from the analysis of the collected GNSS observations were adopted into the numerical simulation models. The GBAS availability under the ionospheric plasma bubbles were re-evaluated with the updated numerical simulation models. Significant degradation of the GBAS availability due to the plasma bubbles in a low magnetic latitude region during a high solar activity period was reacknowledged through the renewed simulations. The effects of the GPS/INS integration to mitigate the degradation were also re-valuated.
Published in:	Proceedings of the 2014 International Technical Meeting of The Institute of Navigation January 27 - 29, 2014 Catamaran Resort Hotel San Diego, California
Pages:	272 - 279
Cite this article:	Fujiwara, T., Tsujii, T., Kubota, T., "Investigation and Modeling of Effects of Ionospheric Plasma Bubbles on GBAS Availability and Its Mitigation by GPS/INS Integration," Proceedings of the 2014 International Technical Meeting of The Institute of Navigation, San Diego, California, January 2014, pp. 272-279.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In