Characterisation of Impact of Scintillations over EGNOS

R. Chaggara, B. Duparc, J. Soubielle, O. Nouvel, A. Billot

Peer Reviewed

Abstract:	An increase of the solar activity is observed since 2010 as part of Solar Cycle #24. This affects the ionosphere behavior and impacts in particular SBAS performance. This Presentation presents the impact of strong ionospheric conditions on EGNOS System with illustrations based on recent observations. Different types of degradations are observed depending on regions considered. While the southern reference stations are affected by the high solar flux that occurs at equatorial crest level, the northern station are subject to geomagnetic perturbations that are typical for polar regions. In contrast with high TEC episodes where high temporal and spatial TEC gradients impact is mainly limited to the south of the ECAC region, scintillations effects concern both the North and the South. Nevertheless, it has been observed that the nature of the effect may be different with regard to the concerned location. In other terms the observed impacts of these scintillations are not exactly the same for all stations. Ionospheric scintillations occur mainly near the magnetic equator and at high latitudes. They have a solar cycle dependence reaching their maximum amplitude during the 11 year solar cycle maximum, and a seasonal dependence depending on the longitude and latitude. Nevertheless, in principle, such phenomena may occur anywhere on Earth regardless the phase of the solar cycle. Ionospheric scintillations at low latitudes (generally designated by equatorial scintillation) occur mainly after the sunset, their main impact on GPS signals concerns amplitude variations whereas. At higher latitudes (boreal scintillation) signal amplitude variations are much less observed giving place high phase scintillation. In this paper, a focus is made on the different effects of auroral and equatorial scintillations on EGNOS reference receivers. Results are mainly based on stations signal quality and validity monitoring and analysis performed by ESSP (European Satellite Services Provider). Main parameters considered to perform this study include: - EGNOS reference station indicators and parameters like signal to noise ratio, loss of lock and cycle slips. - Independent ionospheric indicators such as geomagnetic Ap and AATR indices [3]. First outcomes indicated in particular that loss of locks of L2 signals are mainly observed over northern stations. Southern stations however are potentially suffering from degraded tracking performance on both L1 and L2. The temporal and spatial characterization of scintillation across EGNOS reference stations is then deeply investigated. For example, in both Southern and Northern stations, measurements are generally degraded for low elevation line of sights. The number of lines of sights impacted and the number of RIMS affected are tightly linked to the strength of the geomagnetic storm. In the South, most impacted measurements are those oriented towards the South and effects are generally concentrated on few reference stations in relation with their geographical repartition. Finally, an overview of the impact of scintillation phenomena on EGNOS navigation service performance is provided thorough illustrations based on most recent observations.
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	3826 - 3832
Cite this article:	Chaggara, R., Duparc, B., Soubielle, J., Nouvel, O., Billot, A., "Characterisation of Impact of Scintillations over EGNOS," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 3826-3832.
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