The Northwest European Loran-C System (NELS) is established by Denmark, Germany, France, Ireland, the Netherlands and Norway to offer a regional, terrestrial radionavigation system for Northwest Europe.
The establishment of NELS has acted as a stimulus to Loran-C research and development at European universities and scientific laboratories. One result of this activity is the development by the Delft University of Technology in the Netherlands of an integrated navigational system called Eurofix. Eurofix is an integrated radionaviagtion and communication system, which combines Loran-C and DGPS by sending differential satellite corrections to users as time, modulated signal information. Loran-C or Chayka stations are upgraded to broadcast low-speed data over ranges of up to 1000km. Data is separated into eight channels which are assigned to DGPS, DGLONASS, DLoran-C/DChayka, navigation integrity messages and short message service. Three channels are reserved for future applications. The normal navigational operational mode of Loran-C is preserved which gives the Eurofix user, next to accurate DGPS positions, improved navigation reliability. If either GPS or Loran-C might fail, the other system still provides position information, however at a reduced accuracy of between 100 to 300 metres. As Loran-C and GPS are highly dissimilar in operational control and signal propagation characteristics, there is not much risk that both systems will fail simultaneously.
Eurofix test transmissions from the Loran-C station at Sylt in Germany have been successful, resulting in a decision to implement Eurofix on another three stations: Lessay (France), Vasrlandet and B0 (Norway) offering Eurofix coverage throughout the area of the current NELS Loran-C coverage.
A plan for full implementation of Eurofix on all NELS stations has now been accepted by the NELS Steering Committee, the system's supreme authority.
Subject to such implementation, there is a potential for further Eurofix coverage expansion in Europe by making use of the existing Loran-C infastructure in the Mediterranean Sea area and the Russian Chayka (Loran-C equivalent) infastructure.
Eurofix can act as a DGPS system when using a Loran-C standard GPS correction output message fed into a suitably equipped GPS receiver system. It does also allow position calculation using both DGPS and Loran-C and comparison of the two systems. If either system fails, the other can take over thus improving availability and continuity. Finally, Eurofix allows full DGPS/Loran-C integration which in a given situation will make for instance, Loran-C act as a satellite source. A user will, in this example, be able to calculate a three dimensional position with only three satellites available.
The coverage of Eurofix is estimated to be at least 1000 km from each Eurofix equipped Loran-C transmitter. Fully implemented, an absolute accuracy of better than 5 metres and an availability of better than 999996% per month is achievable.
The NELS Eurofix programme is fully in line with the EU's policy on radionavigation system development in Europe.
2. Answer the following questions
1. Why have differential GPS (DGPS) services been developed?
2. What is the fundamental principle of DGPS?
3. What methods of supplying corrections exist?
4. What does the pseudorange technique involve?
5. What countries is NELS established by and for what?
6. What is Eurofix?
7. What level can Eurpfix coverage be estimated?
3. Discuss recent radionavigation system developments.
Список использованной литературы
1. Навигационные пособия Великобритании и США. Условные обозначения на адмиралтейских картах и планах. Одесса: Студия Негоциант, 2002.
2. Шишкин А.В., Купровский В.И., Кошевой В.М. Глобальная морская система связи для безопасности мореплавания. Одесса: ОГМА, 1998
3. Admiralty List of Radio Signals. Vol.8, NP288
4. Brown’s Nautical Almanac, 2003.
Ó Ирина Витальевна Чарова