Loran-C still needed to back up Satellite systems
IT IS PRACTICALLY certain that satellite navigation will be
the preferred system of radionavigation for the foreseeable future.
However, all expert authorities agree that a prudent mariner will
not rely solely on a single system. Satellite navigation systems
should, therefore, always be backed up and cross-checked by a fully
independent alternative system.
The alternative system preferred by the Commissioners of Irish
Lights is Loran-C. The Commissioners are supported in this view by
the two British General Lighthouse Authorities (Trinity House and
the Northern Lighthouse Board) and by IALA (The International
Association of Aids to Marine Navigation and Lighthouse
Authorities), as well as by many influential national and
international interested bodies.
Loran is an acronym for Long range navigation. The original Loran system (now referred to as Loran-A) was developed for military use in the United States during the second world war as a similar, but superior, system to Decca. Loran-C is the modern, more sophisticated version.
The system was made available for civilian use in 1974.
Outside the United States and Canada Loran-C transmitters were installed at strategic locations by agreement with the host countries, but in the early 1990s the USA announced it had no future military use for the system and would authorise the transfer of the transmission stations to the host countries for civilian use.
In accordance with European Union policy, and to ensure the provision of adequate radionavigation services, Denmark, France, Germany, Ireland, The Netherlands, and Norway have adopted Loran-C as an alternative to satellite navigation systems and by international agreement in 1992 have set up a regional Loran-C system named the Northwest European Loran-C System (NELS).
To provide full and accurate coverage throughout north-west Europe, and especially off south-west Ireland and in the Bay of Biscay, a new Loran-C station in Ireland is required in addition to the existing stations elsewhere in the NELS area. Legal and planning difficulties have delayed the construction of this transmitter. The legal difficulties have been resolved but political difficulties remain.
Because of the need for an alternative radionavigation system to satellite systems the Commissioners of Irish Lights believe that the construction of an Irish Loran-C transmitter as soon as possible is essential to complete the NELS infrastructure.
The only satellite system at present in widespread use is the United States's Global Positioning System (GPS), for which a variety of inexpensive receivers is available for different applications. Use of the Russian glonass system is restricted because of the present incomplete constellation of satellites and the limited availability of receivers to commercial users. Both of these systems are designed primarily for military use. Meanwhile, the proposed international Global Navigation Satellite System (gnss) remains little more than an idea.
Although satellite navigation systems have many advantages they also have inherent weaknesses. However, Loran-C has inherent strengths that compliment and counterbalance the weaknesses of satellite systems.
Satellites transmit relatively weak, high frequency signals that are subject to interference by disturbances in the ionosphere. The signals can easily be jammed, either intentionally or otherwise. Loran-C transmits high strength, low frequency signals; furthermore, the groundwave signals that travel over the curvature of the earth from Loran-C transmitters are subject to little distortion or interference. Loran-C receivers detect a specific part of the groundwave signal but reject the skyware signals that are deflected back to earth by the ionosphere and are subject to distortion and interference.
Loran-C is earth based and easily accessible for maintenance and repair unlike satellite systems which, obviously, are space-borne and not easily accessible in the event of system failure.
Loran-C is under the control of civil administrations established in various regions of the world by the participating states under international treaties; but GPS is under the military control of one country, the USA, which reserves the right to re-impose selective availability (which downgrades the signal) or even switch the system off without warning at any time. There are no binding international agreements or institutional arrangements outside the USA to safeguard the future availability of GPS for civil use.
The combination of Loran-C and GPS results in a hybrid system with greater accuracy, availability, and integrity than either system alone. Combined coverage by satellite and Loran-C facilitates a high degree of system verification and cross-integrity checking, particularly when applied to integrated systems and electronic charts.
Eurofix transmits GPS differential data from Loran-C station using a data channel. The data channel provides corrections to satellite derived positions and indicates the degree of integrity of the satellite information. An integrated Loran-C/Eurofix/ GPS receiver can be used for position fixing and navigating with great accuracy utilising differential GPS via Eurofix. Should the GPS signal fail (as will happen in cities, forests, mountainous areas, tunnels, or underground car-parks) the Loran-C signal which has been calibrated by dGPS will continue to provide a navigation service. Should the Loran-C signal fail and consequently the Eurofix signal, navigation can continue with GPS alone. This integration of Loran-C/Eurofix/GPS to provide a navigation service even if one of the basic services has failed fulfils the mariners sensible approach in not relying on a single system for the safety of navigation.
During the year 2000 the fourth and final Loran-C station in the first phase of NELS's plan to implement Eurofix commenced transmission of Eurofix data. The Eurofix Loran-C/DGPS transmissions provide high accuracy position fixing over long ranges.
Loran is an acronym for Long range navigation. The original Loran system (now referred to as Loran-A) was developed for military use in the United States during the second world war as a similar, but superior, system to Decca. Loran-C is the modern, more sophisticated version.
The system was made available for civilian use in 1974.
Outside the United States and Canada Loran-C transmitters were installed at strategic locations by agreement with the host countries, but in the early 1990s the USA announced it had no future military use for the system and would authorise the transfer of the transmission stations to the host countries for civilian use.
In accordance with European Union policy, and to ensure the provision of adequate radionavigation services, Denmark, France, Germany, Ireland, The Netherlands, and Norway have adopted Loran-C as an alternative to satellite navigation systems and by international agreement in 1992 have set up a regional Loran-C system named the Northwest European Loran-C System (NELS).
To provide full and accurate coverage throughout north-west Europe, and especially off south-west Ireland and in the Bay of Biscay, a new Loran-C station in Ireland is required in addition to the existing stations elsewhere in the NELS area. Legal and planning difficulties have delayed the construction of this transmitter. The legal difficulties have been resolved but political difficulties remain.
Because of the need for an alternative radionavigation system to satellite systems the Commissioners of Irish Lights believe that the construction of an Irish Loran-C transmitter as soon as possible is essential to complete the NELS infrastructure.
The only satellite system at present in widespread use is the United States's Global Positioning System (GPS), for which a variety of inexpensive receivers is available for different applications. Use of the Russian glonass system is restricted because of the present incomplete constellation of satellites and the limited availability of receivers to commercial users. Both of these systems are designed primarily for military use. Meanwhile, the proposed international Global Navigation Satellite System (gnss) remains little more than an idea.
Although satellite navigation systems have many advantages they also have inherent weaknesses. However, Loran-C has inherent strengths that compliment and counterbalance the weaknesses of satellite systems.
Satellites transmit relatively weak, high frequency signals that are subject to interference by disturbances in the ionosphere. The signals can easily be jammed, either intentionally or otherwise. Loran-C transmits high strength, low frequency signals; furthermore, the groundwave signals that travel over the curvature of the earth from Loran-C transmitters are subject to little distortion or interference. Loran-C receivers detect a specific part of the groundwave signal but reject the skyware signals that are deflected back to earth by the ionosphere and are subject to distortion and interference.
Loran-C is earth based and easily accessible for maintenance and repair unlike satellite systems which, obviously, are space-borne and not easily accessible in the event of system failure.
Loran-C is under the control of civil administrations established in various regions of the world by the participating states under international treaties; but GPS is under the military control of one country, the USA, which reserves the right to re-impose selective availability (which downgrades the signal) or even switch the system off without warning at any time. There are no binding international agreements or institutional arrangements outside the USA to safeguard the future availability of GPS for civil use.
The combination of Loran-C and GPS results in a hybrid system with greater accuracy, availability, and integrity than either system alone. Combined coverage by satellite and Loran-C facilitates a high degree of system verification and cross-integrity checking, particularly when applied to integrated systems and electronic charts.
Eurofix transmits GPS differential data from Loran-C station using a data channel. The data channel provides corrections to satellite derived positions and indicates the degree of integrity of the satellite information. An integrated Loran-C/Eurofix/ GPS receiver can be used for position fixing and navigating with great accuracy utilising differential GPS via Eurofix. Should the GPS signal fail (as will happen in cities, forests, mountainous areas, tunnels, or underground car-parks) the Loran-C signal which has been calibrated by dGPS will continue to provide a navigation service. Should the Loran-C signal fail and consequently the Eurofix signal, navigation can continue with GPS alone. This integration of Loran-C/Eurofix/GPS to provide a navigation service even if one of the basic services has failed fulfils the mariners sensible approach in not relying on a single system for the safety of navigation.
During the year 2000 the fourth and final Loran-C station in the first phase of NELS's plan to implement Eurofix commenced transmission of Eurofix data. The Eurofix Loran-C/DGPS transmissions provide high accuracy position fixing over long ranges.