Most of the information posted in this document was done before the closure of the US Loran-C chain in February 2010. It remains here for reference purposes.
FUTURE OF LORAN-C
In the United States, the Loran Service Unit (LSU) is the engineering center for Loran-C; NAVCEN is the operations center, and USCG HQ is the program center.
Under the 1994 U.S. Federal Radionavigation Plan, with GPS promised as better performing replacement, the Department of Transport advanced the phase-out date of Loran-C from 2015 to December 31, 2000, dealing a body blow to the system operated by the US Coast Guard. Outside the US, the Coast Guard left individual countries to decide whether to continue their own operations.
In Canada, as part of the Marine Aids Modernization program, the Canadian Coast Guard (CCG) is evaluating the impact of the proposed discontinuance of Loran-C navigation service. The objectives of the impact study are to identify the Loran-C users; to evaluate the present use of the system in relation to the introduction of new technologies such as GPS/DGPS and Electronic Chart Display and Information Systems (ECDIS); and to identify the availability of suitable alternatives to providing and funding the current service. It is believed that the demand for Loran-C will decline as new technologies, such as GPS and DGPS, become recognized as reliable and accurate navigation systems. In the Royal Canadian Navy, Loran C was fitted in all the "steamers" during its popularity but all those ships are now paid off. At this time, the system is being removed from the AOR's and the 280 Iroquois class ships.
At this time, there are 5 transmitting sites in Canada, namely Cape Race (Nfld.), Comfort Cove (Nfld.) and Fox Harbour (Labrador) on the east coast and Port Hardy (B.C.), Williams Lake (B.C.) on the west coast. In addition, there are 4 control and monitor sites at St. Anthony (Nfld.), Williams Lake (B.C.), Montague (P.E.I), and Sandspit (B.C.). The total estimated cost of the Loran-C program in Canada is $2.229M.
A study being carried out by the Goss Gilroy company will include in-depth telephone interviews with Loran-C interest groups. Following this, a questionnaire will be specially developed and distributed nationally to marine and non-marine user groups. The study will also include eight national focus groups and a benefit cost study of possible alternatives. All of this is expected to be completed by early 2000. The CCG’s proposed discontinuance of Loran-C in Canada is not directly related to the United States (U.S.) 1994 & 96 Federal Radio Navigation Plan announcement, although coordination with the U.S. would be required.
In 1997, an independent study was conducted in the U.S. to evaluate the impact of discontinuing Loran-C. Finally, on June 29, 1998, a decision was made by FAA, USCG and OST to continue the operation of Loran-C beyond its currently planned 12/31/00 termination date. At the ICAO CNS/ATM implementation conference held in Rio de Janeiro, the FAA dropped a bombshell by announcing, contrary to all earlier assurances, that the Global Positioning System (GPS) would not be approved for sole use navigation, and would need a backup. The reason given was that the possibilities of jamming, solar events, etc., were now better understood. Excellent though GPS may be, its problem is that it is so low powered that the signal can easily be blanked out or disrupted - as demonstrated at an 1997 Moscow air show where a jammer destroyed the signal over a radius of 200 km. The notion of GPS as sole means of navigation is dead. Suitable backup systems cited are triple inertial, VOR/DME and LORAN-C.
Bob Moody, K7IRK, spent half of his career launching payloads on high altitude balloons and tracking them across the USA with light twins (Cessna 310). He recalls. "At various times we used LORAN, OMEGA, VOR, ADF, RADAR, Transponders, GPS, GMD, MK II Eyeballs and dead reckoning to track them. GPS is by far the best system displaying not only position, but also course, speed altitude and time. GPS is now so good that it's easy to become complacent. But when it goes away. And it does from time to time, you better have a backup!"
The implications of the FAA's new position are many - ranging from the need to maintain a ground based ILS and VOR/DME/NDB navigation aids system way beyond the time scale the world had been led to expect, to the probable continued operation of LORAN-C chains. As of September 1998, the American DoT confirmed that the existing LORAN-C chains will be maintained and upgraded, at least to 2008, "in the transition period to satellite based navigation".
Linn Roth, President of the International Loran Association (1999-2000) published a white paper which underscores the need for Loran-C to be a backup for GPS for at least 15 more years. While public debate over national GPS policy appears to be moving away from GPS as a sole-means system, it is interesting to note that industry has recognized the realities of the situation and provided backups all along. For example, commercial airlines carry a number of redundant, dissimilar systems, and no major carrier has equipped even half a fleet with GPS receivers, choosing reliance on these other systems until GPS augmentation programs are clarified, implemented and proven. Telecommunication and power grid systems rely on GPS as their primary timing reference for network synchronization, but incorporate Loran receivers or Rubidium oscillators to carry over in case of GPS interruption. Although not generally understood, GPS-based car navigation systems typically integrate differential wheel counters and digital map matching technologies in order to compensate for GPS’ poor penetration into urban environments.
From a physical perspective, Loran and GPS have very different characteristics. In essence they complement each other: ground vs. satellite based, low vs. high frequency, high signal level vs. low signal level. Consequently they do not suffer from the same modes of failure so they should in theory, never fail simultaneously. Loran or GPS will be always be available to provide better performance under conditions where one system might be compromised. Loran’s wavelength and signal strength enable it to penetrate into areas where GPS has difficulty because of line-of-sight blockage as in urban or forested situations. Loran can even penetrate some buildings. In fact, the Defense Advanced Research Project Agency (DARPA) has explored combined receivers that could be used to locate troops in urban environments. Loran penetration into cities and its ability to provide an indefinite backup to GPS in timing applications are two additional advantages Loran provides in telecommunication applications.
Within Europe, the European Union promotes the development of Loran-C chains under the auspices of NELS (Northwest European Loran-C System). The ownership of each of the facilities within NELS is vested in the state on whose territory the facility is located. Superior direction of the system is exercised by a Steering Committee where all members are represented. A Coordinating Agency is appointed for implementation of directives given by the Steering Committee and to coordinate the establishment and operation of the system. Norway accepts the role as Coordinating Agency.
The most recent draft European Radio Navigation Plan (ERNP) and European Commission report (31/10/96) includes Loran-C as part of the desired system mix in marine, land transport and aviation to at least the year 2020. In north-west Europe, where Loran is used primarily for air to land and maritime navigation, and where the GPS/DoT lobby was not so strong, Denmark, France, Germany, Ireland, Norway and the Netherlands teamed up to form NELS with the expectation to modernize existing transmitters and establish some new ones. NELS, up and running since April 1998, with the exception of the delayed Irish station, may be enlarged to include two Italian stations to extend coverage in the Mediterranean. This expansion would include a linkup with the Russian Chayka system, which can also be received by the modern Loran receivers, in the western Arctic, the Baltic (Belarus) and the Crimea.
It appears on the cards that the DoT will extend and modernize the Loran-C system as an economical backup to GPS, at least until 2008, or until the arrival of a failsafe GNSS-2, under international control.
ENHANCED LORAN-C DATA CHANNEL PROJECT
Research efforts are underway to increase the data carrying capability of the Loran-C Data Channel using combinations of previously developed modulation techniques. The purpose of this is to provide a unidirectional communications information for Global Positioning System (GPS) integrity and potentially for GPS correction data.
Several different methods are under evaluation: Pulse-Position Modulation (PPM), Supernumerary Interpulse Modulation (SIM), Intrapulse Frequency Modulation (IFM), and/or Hybrid combinations of these. These are beyond the scope of this document so they will not be explained here.
In addition to the above, the FAA is assessing Loran developments in four key areas:
1) Development of a Loran H-field antenna suitable for aircraft installation
2) Development of an RTCA DO-194/FAA TSO-C60b compliant Digital Signal Processing (DSP)
3) Development of enhanced Loran communications capability for GPS integrity and potentially for
GPS correction data.
4) Development of a hybrid GPS/Loran receiver architecture.
The Enhanced Loran-C Data Channel project concentrates on the third of these four objectives. Existing or proposed equipment may not be capable of actual transmissions of all of these modulation formats. Stanford University, the USCGA, and the LSU are cooperating to evaluate viable data formats and technology to permit the modulation and demodulation of data messages transmitted via modulation of Loran-C signal pulse(s).
The basic GPS service fails to meet the accuracy (the difference between the measured position at any given time to the actual or true position), availability (the ability of a system to be used for navigation whenever it is needed by the users, and its ability to provide that service throughout a flight operation), and integrity (the ability of a system to provide timely warnings to users or to shut itself down when it should not be used for navigation) requirements critical to safety of flight.
In order to meet these requirements, the FAA is developing the Wide Area Augmentation System or WAAS. WAAS is a safety-critical navigation system that will provide a quality of positioning information never before available to the aviation community. It is what the name implies, a geographically expansive augmentation to the basic GPS service. The WAAS improves the accuracy, integrity, and availability of the basic GPS signals. This system will allow GPS to be used as a primary means of navigation for en route travel and non-precision approaches in the U.S., as well as for Category I approaches to selected airports throughout the nation. The wide area of coverage for this system includes the entire United States and some outlying areas such as Canada and Mexico.
The WAAS signal has enough capacity to carry both the differential corrections and the integrity data required to augment GPS. Loran-C could also provide a land based data channel supplement to Space Based Augmentation Systems (SBAS), like WAAS. The inherent integrity and robustness of the Loran-C signal may obviate the need for some error correction overhead, thereby reducing the data rate required for transmission of WAAS messages using Loran-C to an achievable level. Loran-C also provides a readily available, extremely reliable, strong (+6 to +10 dB SNR) signal over all of the Contiguous United States and Alaska.
Besides supplementing SBAS, other potential uses of the Loran-C data link are possible. It could be used for differential Global Positioning System, (DGPS) corrections, differential Global Navigation Satellite System (DGNSS) corrections, contingency control of the Loran-C system during loss of landline communications, and differential Loran-C corrections.
Of specific concern is the ability to transmit WAAS messages. In the past, the USCG has accomplished data
transmissions on Loran-C using Pulse-Dropping techniques, Polyphase Communications (PM) Modulation, Clarinet Pilgrim (CP), and Two-Pulse Communications (TPC). Currently, the EUROFIX (possibly known as Loran Comm or Lorsat) system is correctly transmitting DGPS correction information in Europe. Unfortunately, none of these techniques provide enough bandwidth to transmit the WAAS message format. The fundamental problem is to develop a Loran-C signal data channel with enough bandwidth to satisfy WAAS requirements. If we can meet WAAS bandwidth requirements, other less bandwidth hungry applications are easily satisfied.
The entire white paper on which this summary is based used to be available at: http://www.uscg.mil/hq/lsu/wepage/papers/Bonn_LSU_final.htm . It is no longer posted.
LATEST NEWS ABOUT LORAN-C
November 2005 - Recently the NELS (Northwest European Loran-C System) organization announced that NELS will be discontinued on January 1st, 2006. In December further info will be provided about the future of the other Loran-C stations in Europe.
The Norwegian Government has decided to close down the Norwegian Loran-C stations Berlevag, Bo,Vaerlandet and Jan Mayen on 5-1-2006 at 1200 UTC.
Both the German station at Sylt and the Danish station at Ejde will shut down on 1-1-2006 at 0000 UTC.
(quote from Worldwide Utility News)
December 2005 - Extended operation of Loran-C at the Norwegian stations
The Government will continue the operation of the four Norwegian Loran-C stations, Værlandet (Askvoll Municipality in Sogn og Fjordane), Bø in Vesterålen (Nordland), Berlevåg (Finnmark), and Jan Mayen, in 2006. The reason for this is the renewed interest in this terrestrial navigation system in Europe. (09.12.05)
Denmark has decided to continue the operation of the Danish Loran-C station at Ejde.
Germany’s decision to discontinue the operation of its LORAN C station Sylt remains unchanged. However, the station Sylt will not, as originally planned, be switched off on 3 January 2006, but the operation will be
continued until the measures required for the conversion of the time synchronization have been carried out. It is
expected that these measures will take about 4 to 5 weeks. It cannot yet be predicted whether the station Sylt will be reactivated at a later time in a different provider organization. This depends on whether it will be possible to find a binding and sustainable new concept for LORAN C applying to all of Europe.
Kirsten Ullbæk Selvig
Chairman NELS Steeringv Committee
(Source: NELS web site)
LORAN-C Data Channel (LDC) 9th Channel Testing Commences
This extract is taken from the USCG Loran-C web page.
"LORAN-C Data Channel testing is part of the on-going effort between the Federal Aviation Administration and the U.S. Coast Guard to modernize the LORAN-C system. The LORAN Data Channel (LDC) will provide information using pulse position modulation of the broadcast signal. The proposed pulse position modulation would be used to broadcast up to sixteen message types including but not limited to station identification, absolute time, early skywave warnings, and differential LORAN correction messages.
The proposed method will use an additional pulse added one thousand microseconds after the eighth pulse on a secondary transmitting station and between the current eighth and ninth pulses on Master.The FAA and Coast Guard began conducting LDC on-air tests in July of 2005. The test broadcast will use pulse position modulation of a ninth pulse added one thousand microseconds after the standard pulse group as described above. Throughout the test period the signal will meet all service performance parameters published in the 1994 specification of the LORAN-C Signal. Users should not experience any tracking errors or service interference from this test broadcast. Users will be notified through Notice to Mariners and Notice to Airmen of any changes to the test schedule and when the testing is completed.
Initial testing was conducted with the LORAN Support Unit in Wildwood, NJ broadcasting the LDC information on 9960-T. Phase 1 of the testing involved broadcasting from LORAN Station Jupiter, FL (7980-Y). Phase 2 added the LDC capabilities to LORAN Station Las Cruces (9610-X) and testing was conducted from 1510Z on 27 Oct 2005 to 0126Z on 07 Nov 2005. LORAN Station Seneca, NY (8970-X) began broadcasting the LDC at 1500Z on 21 Dec 2005. LORAN Station Las Cruces, NM will being broadcasting LDC continuously beginning on 01 Apr 2006". (See the web site for the diagram which shows the estimated coverage once all three of the stations are on the air.
Each Loran station will initially transmit the basic Station Identification/Time message only with exception of Loran Station Seneca. Loran Station Seneca will also broadcast differential LORAN corrections for additional research. Each transmitted message will include a “test mode” bit to warn users that the information in the message is for research ONLY. As testing continues, there is a high probability of incorporating additional messages. Each new message will have an indicator that it is for testing purposes only".
Credits and References:
1) Loran Data Channel http://www.navcen.uscg.gov/loran/9th-pulse-modulation-ldc.html
2) Bob Moody <bob(at)vanirmail.com>