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1 2010

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Accuracy Performance of eLORAN for Maritime Applicaations

Safar J., Lebekwe C. K., Williams P.

Annual of Navigation

2010

No. 16

109-121

E-Loran, or enhanced Loran, is the latest in the longstanding and proven series of low frequency, LOng-RAnge Navigation systems. eLoran evolved from Loran-C in response to the 2001 Volpe Report on GPS vulnerability. It improves upon previous Loran systems with updated equipment, signals, and operating procedures. The improvements allow eLoran to provide better performance and additional services when compared to Loran-C, and enable eLoran to serve as a backup to satellite navigation in many important applications. Different applications impose specific requirements on the navigation system's accuracy, availability, integrity and continuity performance. In the maritime sector, accuracy requirements are the most stringent. In order to comply with the requirements of the International Maritime Organisation (IMO) for harbour entrance approach, eLoran has to provide an accuracy of better than 10 m (95%). Achieving this target is possible if the eLoran navigation receiver is equipped with an up-to-date database of signal propagation corrections and if real-time differential Loran corrections are applied. When these conditions are met, the achievable accuracy is largely determined by the transmitters' geometry, signal strengths and atmospheric noise levels, but also by the mutual interference among eLoran stations. This is also referred to as Cross-Rate Interference (CRI) and is inherent to the way all Loran systems operate. In this paper we present results of the eLoran research that is being conducted at the Czech Technical University in Prague (CTU) and the University of Bath (UK) in cooperation with the General Lighthouse Authorities of the United Kingdom and Ireland. In our work we have focused on questions that arise when considering introducing new eLoran stations into an existing network. This particular paper investigates the achievable accuracy performance of eLoran for maritime applications. The sources of measurement error in eLoran are reviewed, and an eLoran accuracy performance model is presented. Special attention is paid to the problem of CRI and possible ways of its mitigation. This paper is an abridged version of a more detailed unpublished paper which can be found at the following address: http://safar.me.uk/pub/js_cl_pw_navsup_2010.pdf.