Accuracy Performance of eLORAN for Maritime Applicaations
Treść / Zawartość
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 This paper is an abridged version of a more detailed unpublished paper which can be found at the following address: http://safar.me.uk/pub/js_cl_pw_navsup_2010.pdf.
Bibliogr. 17 poz., rys., tab.
-  Basker S., Williams P., Bransby M., Last D., Offermans G., and Helwig A., Enhanced Loran: Real-time maritime trials, in Proceedings of Position, Location and Navigation Symposium, 2008 IEEE/ION, 2008.
-  Clynch J., The Hunt for RFI — Unjamming a Coast Harbor, January 2003, Available: http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=43404.
-  Forssell B., Radionavigation Systems, Artech House, 2008.
-  Grant A., Williams P., Ward N., and Basker S., GPS Jamming and the Impact on Maritime Navigation, The Journal of Navigation, 2009, Vol. 62, pp. 173–187.
-  Hargreaves C., GAARDIAN WP3 — GLA03 Analysis of Timing Data in Raw Loran Data, General Lighthouse Authorities of the UK and Ireland, Tech. Rep., 2010.
-  ITU-R P.1147-2, Prediction of Sky-wave Field Strength at Frequencies Between About 150 kHz and 1700 kHz, International Telecommunication Union, 2003.
-  ITU-R P.372-9, Radio Noise, International Telecommunication Union.
-  ITU-R P.832-2 World Atlas of Ground Conductivities, International Telecommunication Union, January 1999.
-  Johnson G., Dykstra K., Oates C., Swaszek P., and Hartnett R., Navigating Harbors at High Accuracy Without GPS: eLoran Proof-of-Concept on the Thames River, in Proceedings of ION National Technical Meeting, 2007, Vol. 2.
-  Lo S., Peterson B., Boyce C., and Enge P., Loran Coverage Availability Simulation Tool, in Proceedings of the Royal Institute of Navigation (RIN) NAV08/ International Loran Association 37th Annual Meeting, 2008.
-  Loran-C receivers for ships — Minimum performance standards — Methods of testing and required test results, British Standards Institution Std. BS EN 61075:1993.
-  LORAN-C USER HANDBOOK. U.S. Department of Transportation, United States Coast Guard, 1992.
-  NAVSTAR GLOBAL POSITIONING SYSTEM INTERFACE SPECIFICATION IS-GPS-200, 2006, revision D.
-  Pelgrum W., New Potential of Low-Frequency Radionavigation in the 21st Century, Ph.D. dissertation, TU Delft, Delft, 2006.
-  Safar J., Lebekwe C. K., and Williams P., Accuracy Performance of eLoran for Maritime Applications. Unabridged, September 2010, Available: http://safar.me.uk/pub/js_cl_pw_navsup_2010.pdf.
-  Safar J., Williams P., Basker S., and Vejrazka F., Cross-Rate Interference and Implications for Core eLoran Service Provision, in Proceedings of the International Loran Association 38th Annual Meeting, Portland ME, 2009.
-  Williams P. and Last D., Extending the range of Loran-C ASF modelling, in Proceedings of the 33th Annual Convention and Technical Symposium of the International Loran Association, 2004.