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Accuracy performance of e-Loran receivers under Cross-Rate Interference conditions

Šafář J., Williams P., Vejražka F.

Annual of Navigation

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2012

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No. 19, part 1

133--148

EN

According to a recent Business Case produced by the General Lighthouse Authorities of the United Kingdom and Ireland (GLAs), e-Loran is the only system that, when combined with GNSS, can achieve cost effective resilient Positioning, Navigation and Timing (PNT) by 2018 for maritime e-Navigation. The GLAs currently operate a trial e-Loran service from Harwich, UK and are working towards establishing e-Loran Initial Operational Capability (IOC) in the seven busiest UK ports and port approaches by mid-2013. A future extension of e-Loran coverage to the entire GLA service area will require the installation of additional transmitting stations. When planning the installation of e-Loran transmitters service providers will need a good understanding of the effects of the new signals on the system’s performance. Since all e-Loran stations share the same frequency band and the e-Loran signals propagate over vast distances, special attention needs to be paid to the issue of intra-system interference. This is also referred to as Cross-Rate Interference (CRI) and is inherent to the way e-Loran operates. In this paper we examine the impact of CRI on the position accuracy performance of e-Loran receivers. First, a signal processing model for a typical e-Loran receiver is developed. This could provide the e-Loran community with a unified framework for receiver performance evaluation. Numerical and, where possible, analytical results obtained from the model are then presented, describing the achievable accuracy performance under different interference conditions. The theoretical results are also compared to those obtained from measurements made on a commercially available receiver driven by a signal simulator. Our analysis shows that modern e-Loran signal processing algorithms can achieve a substantial reduction of the negative effects of CRI. However, there is still an appreciable residual effect, which should be taken into account when designing future e-Loran networks and determining their coverage and performance.

2

Assessing the Limits of eLoran Positioning Accuracy

Safar J., Vejrazka F., Williams P.

TransNav : International Journal on Marine Navigation and Safety of Sea Transportation

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2011

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Vol. 5, no. 1

93--101

EN

Enhanced Loran (eLoran) 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. The next generation of the Loran systems, eLoran, improves upon Loran-C through en-hancements in equipment, transmitted signal, 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. The Czech Technical University in Prague (CTU) participates in the eLoran research activities coordinated by the General Lighthouse Authorities of the United Kingdom and Ireland (GLAs). In our work we have focused on questions that arise when considering introducing new eLoran stations into an existing network. In particular, this paper explores the issue of Cross-Rate Interference (CRI) among eLoran transmissions and possible ways of its mitigation at the receiver end. An eLoran receiver performance model is presented and validated using an experimental eLoran signal simu-lator developed by a joint effort of CTU and GLAs. The resulting model is used to evaluate the achievable positioning accuracy of eLoran over the British Isles.

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Accuracy Performance of eLORAN for Maritime Applicaations

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

Annual of Navigation

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2010

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No. 16

109-121

EN

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.

4

Visualization of integrated knowledge for sustainable development decision making – the Natural Resources of Canada Example

Siekierska E., Richardson D., Muller A., Williams P., Francis K., Turner G.

Archiwum Fotogrametrii, Kartografii i Teledetekcji

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2003

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Vol. 13a

209--218

EN

Visualization refers to visual perception of various types of graphic representation of geospatial information ranging from static to dynamic presentation (cartographic visualization) to exploratory data analysis (scientific visualization). The project entitled Visualization of Integrated Knowledge for Sustainable Development Decision Making, recently initiated in Natural Resources Canada, Earth Sciences Sector, focuses primarily on the former: Web-based, interactive, dynamic representation of information, suitable for effective communication of geospatial concepts in support of decision making. The general objective of the visualization project is to explore, develop and implement visualization techniques capable of translating complex scientific information into a form that readily communicates sustainable development forecast scenarios to various user groups, in particular to policy decision makers in the federal government of Canada. The project is carried out in support of the “Sustainable Development through Knowledge Integration” program. The selected applications, to demonstrate knowledge integration issues for sustainable development decision making, are: sustainable use of energy, sustainable management of forests, sustainable management and rehabilitation of mines, and responsiveness to natural hazards. Visualization tools, in particular user-friendly interfaces, can contribute to the increased use of earth sciences information and knowledge and support more effective decision making. The innovative Web-based interactive visualization techniques will facilitate access to information, integration of multi-source data, hypothesis testing, and communication of integrated knowledge. This paper presents an overview of the Sustainable Development through Knowledge Integration (SDKI) program, and the Visualization of Integrated Knowledge for Sustainable Development Decision Making (SDKI-Vis) project, and discusses issues related to effective and ineffective communication of geo-spatial information in the decision support system developed to facilitate information sharing about the Georgia Basin region of Western Canada (the Georgia Basin Digital Library).

PL

Wizualizacja to wizualna percepcja różnych typów geoprzestrzennych informacji od statycznych do dynamicznych prezentacji (wizualizacja kartograficzna) do eksploratywnej analizy danych (wizualizacja naukowa). Niedawno rozpoczęty w Instytucie Nauk o Ziemi, Ministerstwa Zasobów Naturalnych Kanady, projekt “wizualizacja zintegrowanej wiedzy w celu podejmowania decyzji zgodnie z zasadami zrównoważonego rozwoju” przede wszystkim zwraca uwagę na interaktywne, dynamiczne przedstawianie danych w oparciu o siec internetu odpowiedniej dla efektywnej komunikacji danych przestrzennych w celu podejmowania decyzji. Głównym celem projektu wizualizacji jest zbadanie, zastosowanie, udoskonalenie lub skonstruowanie nowych technik wizualizacyjnych, które byłyby w stanie przekazywać kompleksowa wiedze naukowa, w formie odpowiedniej do przedstawienia scenariuszy rozwoju zrównoważonego, dla różnych grup użytkowników, szczególnie decydentów z rządu federalnego Kanady. Projekt jest prowadzony w ramach programu “zrównoważony rozwój w oparciu o integracje wiedzy”. Wybrane przykłady zastosowań demonstrujące podejmowanie decyzji w oparciu o zintegrowana wiedze w celu zapewnienia zrównoważonego rozwoju to: wykorzystanie energii, zarządzanie terenami zalesionymi; rehabilitacja kopalń i zarządzenie górnictwem zgodnie, z zasadami rozwoju zrównoważonego i zapobieganie zagrożeniom naturalnym. Narzędzia wizualizacyjne, a w szczególności łatwa dla użytkownika “nawigacja” (interfejsy), w znacznym stopniu przyczyniają się do efektywnego, do podejmowania decyzji wykorzystania wiedzy i informacji z zakresu nauk o ziemi. Nowoczesne interaktywne techniki wizualizacji, oparte o sieci Internetu) ułatwiają dostęp do informacji, a także integracje danych pochodzących z różnych źródeł, testowanie hipotez i udostępnianie zintegrowanej wiedzy. Niniejsza publikacja zawiera opis programu “zrównoważony rozwój w oparciu o integracje wiedzy”, jak również projektu “wizualizacja zintegrowanej wiedzy w celu podejmowania decyzji zgodnie z zasadami zrównoważonego rozwoju”. Publikacja ta wprowadza również dyskusje problemów związanych z prawidłowym i nieprawidłowym przekazem informacji przestrzennej w systemach do podejmowania decyzji stwarzanych dla ułatwienia dostępu i wymiany informacji na przykładzie systemu informacji o Basenie Georgii w zachodniej części Kanady (Biblioteka Cyfrowa Basenu Georgii).