Ionosphere Impact on GNSS Based Civil Aviation Applications During Maximum Solar Activity

E. Robert, M. Mabilleau, P. Ladoux, D. Duchet

Abstract:	Aviation operations, including navigation, surveillance and timing, increasingly rely on GNSS services. Concerning navigation, ICAO (International Civil Aviation Organization) has decided on the objective to move from operations based on ground radio navigation aids to GNSS based operations for all phases of flight. GNSS is already widely used for the cruise part of the flight and is being further developed for approach and landing operations. The surveillance domain follows the same trend. GNSS based services already enhance radar systems and an increasing part of the surveillance domain will partly rely on GNSS services in the coming years. GNSS performances under nominal ionosphere conditions are already well known. However, before moving towards these GNSS services, the aviation community has to better assess GNSS performances under abnormal ionosphere conditions. Adverse ionosphere conditions affect the GNSS signal travelling and can induce group delay, which will degrade the positioning performances, or scintillation, leading to loss the lock of one or more satellites within the GNSS receiver. The future use of multiple dual frequency GNSS constellation will significantly decrease the impact of these adverse ionosphere conditions. Indeed, the use of two frequencies will enable users to correct the group delay, and the higher number of satellites will efficiently mitigate the scintillation effect. Although dual frequency GPS and GALILEO satellite full operational constellation should be available by 2020+, it is most likely that the majority of the European aircraft fleet will not be equipped with dual frequency multiple constellation receivers before 2030. Therefore, the current 2013 solar cycle is the best opportunity to scale the ionosphere impact and define adequate mitigations for the next 2024 solar cycle. As a consequence, in 2009 EUROCONTROL (European Organization for the Safety of Air Navigation) launched a project to assess the potential solar activity impact on European GNSS civil aviation operations and to identify technical or operational mitigation techniques Within the framework of this project, a network of approximately 250 European GNSS ground stations is used to daily monitor the ionosphere. This monitoring consists of an automatic generation of several per-station-ionosphere parameters and European ionosphere maps. In addition, for some interesting ionosphere events, a manual analysis which further characterizes these events is performed. So far, 7 events in 2011, 2012 and 2013 have been analyzed. During some of these events, ionosphere slant spatial gradients up to 160 mm/Km have been measured over the Canary Islands. European ionosphere scenarios have been built based on the characterization of these ionosphere events associated with past events characterized by other studies during the previous solar cycle. These scenarios are a set of maximum values for different ionosphere parameters related to the Total Electron Content (TEC) but also to scintillations. They consider both significant and worst case ionosphere events and they have been split into geographical regions. A total of 6 scenarios have been defined. At first, those scenarios have been input into a GNSS receiver simulator to assess the ionosphere impact at receiver level. Two receivers reflecting current aeronautical ABAS receivers have been simulated. The output is an impact assessment at receiver level in terms of pseudo-range error, tracking robustness and re-acquisition performance for different elevation angles. Then, based on the receiver behaviour results, the same ionosphere scenarios have been implemented into a service volume simulator. This service volume simulator has been based on the PEGASUS software developed by EUROCONTROL for the GNSS community. This service volume simulator has been used to assess the ionosphere impact at operation level by characterizing the accuracy, integrity and availability of the intended application. ICAO standards as well as equipment standards are used as reference for the application performance requirements.
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:	677 - 689
Cite this article:	Robert, E., Mabilleau, M., Ladoux, P., Duchet, D., "Ionosphere Impact on GNSS Based Civil Aviation Applications During Maximum Solar Activity," Proceedings of the 2014 International Technical Meeting of The Institute of Navigation, San Diego, California, January 2014, pp. 677-689.
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