Demonstrating the Benefits of Resilient PNT

A. Grant, P. Williams, C. Hargreaves, M. Bransby

Abstract:	The General Lighthouse Authorities of the United Kingdom and Ireland (GLA) provide marine aids-to-navigation (AtoNs) for the benefit and safety of all mariners within their waters. These AtoNs include traditional lighthouses, buoys and various radionavigation systems. It is recognised that GPS, or more generally Global Navigation Satellite Systems (GNSS) have become the primary means of obtaining Position, Navigation and Timing (PNT) information at sea. Mariners have been conditioned to believe that GPS is infallible, yet it is known to be vulnerable to space weather events, deliberate interference and system failures. Resilient PNT is an essential requirement for the successful implementation of e-Navigation services for safer and more efficient shipping. e-Navigation is defined by the International Maritime Organisation (IMO) as “the harmonized collection, integration, exchange, presentation and analysis of maritime information onboard and ashore by electronic means to enhance berth to berth navigation and related services, for safety and security at sea and protection of the marine environment”. To achieve e-Navigation, the need for more than one position input to e-Navigation is recognised, backing up GNSS with independent systems. The GLA support the need for resilient PNT, both through their own efforts and through their involvement in the ACCSEAS project. ACCSEAS is a part funded project involving many partners across the North Sea Region (NSR). The project aims to develop an e-Navigation test bed within the NSR which can be used to demonstrate prototype e-Navigation services. Regardless of the function or processes involved in these prototype e-Navigation services, they will all rely on knowing where the affected vessels are and will need integrity in that position. As such, one of the aims of the ACCSEAS project is to develop, and demonstrate, resilient PNT; which it will achieve by investigating a number of potential solutions, including integrated navigation systems, absolute radar positioning, ranging signals from marine beacons and AIS base stations (known as R-mode) and the use of existing systems, such as eLoran. The ACCSEAS project partners have developed a prototype resilient PNT data processor and this paper will explain how this system works and will report on the outcomes of recent resilient PNT demonstrations, held off the coast of Harwich in the UK, where the use of this prototype was demonstrated. This early prototype data processor monitors GPS performance using a number of quality measures and switches to an alternative PNT system if GPS performance falls below the desired quality level. For these demonstrations, eLoran was used as the alternative system, taking advantage of the GLA prototype eLoran programme, and GPS performance was degraded and ultimately denied through the use of a licensed GPS jamming signal. These demonstrations were conducted to show the benefit of having a resilient PNT solution on a typical bridge. They followed the scenario of a vessel steaming, unwittingly, towards a GPS jamming source. As the vessel approached the jamming signal, three phases of interference were observed – no effect, a period of indecision and then GPS denial. The scenario was repeated twice, with the first run demonstrating the effect of losing GPS information and how it affects various bridge systems, leading to a number of alarms. For the second run, the prototype data processor was enabled and the audience were able to see, and hear, the benefit of having such a system. No alarms sounded from the systems fed by the resilient PNT system. This paper reports on how the data processor unit successfully provided the ship bridge systems with eLoran derived data, and how it did so quietly, seamlessly and automatically, enabling the mariner to continue to conduct their operations and navigate safely. This paper reports on a number of real firsts. For the first time a resilient PNT solution was demonstrated publicly on a typical vessel and non-GNSS derived PNT data was used to maintain operation of the many bridge systems, such as the ECDIS, AIS transponder and correcting the drift error in the gyro. Also for the first time, a vessel reported its position over AIS using eLoran derived PNT information. The paper concludes by explaining how the ACCSEAS project will move forward from here over the remaining two years of the project, where it will further develop the different resilient PNT options considered earlier. It will also report on the GLA eLoran programme and the build up towards its Initial Operational Capability. This work demonstrates the GLA wish to show both the need for resilient PNT and the benefits of achieving it, and shows how mariners can continue to maintain situational awareness and safe navigation during periods of GNSS denial.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	598 - 604
Cite this article:	Grant, A., Williams, P., Hargreaves, C., Bransby, M., "Demonstrating the Benefits of Resilient PNT," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 598-604.
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