Loran-C

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A LORAN-C receiver for use on merchant ships

Loran-C is a hyperbolic radio navigation system which allows a receiver to determine its position by listening to low frequency radio signals transmitted by fixed land-based radio beacons. Loran-C combined two different techniques to provide a signal that was both long-range and highly accurate, traits that had formerly been at odds. The downside was the expense of the equipment needed to interpret the signals, which meant that Loran-C was used primarily by the military after it was first introduced in 1957.

By the 1970s the electronics needed to implement Loran-C had been dramatically reduced due to the introduction of solid state radio electronics, and especially the use of early microcontrollers to interpret the signal. Low-cost and easy-to-use Loran-C units became common from the late 1970s, especially in the early 1980s, leading to the earlier LORAN[N 1] system being turned off in favour of installing more Loran-C stations around the world. Loran-C became one of the most common and widely used navigation systems for large areas of North America, Europe, Japan and the entire Atlantic and Pacific areas. The Soviet Union operated a nearly identical system, CHAYKA.

The introduction of civilian satellite navigation in the 1990s led to a very rapid drop-off in Loran-C use. Discussions about the future of Loran-C began in the 1990s, and several turn-off dates were announced and then cancelled. In 2010 the US and Canadian systems were shut down, along with shared Loran-C/CHAYKA stations with Russia.[1][2]

History[edit]

Loran-A[edit]

The original LORAN began as a US Army requirement for an aircraft navigation system offering accuracy of about 1 mile (1.6 km) at a range of 200 miles (320 km), and a maximum range as great as 500 miles (800 km) for high-flying aircraft. During the initial meetings a member of the UK liaison team, Taffy Bowen, mentioned that he was aware the British were also working on a similar concept, but had no information on its performance.

The development team, led by Alfred Lee Loomis, made rapid progress on the transmitter design and tested several systems during 1940 before settling on a 3 MHz design. Extensive signal-strength measurements were made by mounting a conventional radio receiver in a station wagon and driving around the eastern states.[3] However, the custom receiver design and its associated cathode ray tube displays proved to be a bigger problem. In spite of several efforts to design around the problem, instability in the display prevented accurate timing measurements.

By this time the team had become much more familiar with the British Gee system, and were aware of their work on "strobes", a time base generator that produced well-positioned "pips" on the display that could be used for accurate measurement. They met with the Gee team in 1941, and immediately adopted this solution. However, they also found that Project 3 and Gee called for almost identical systems, with similar performance, range and accuracy. But Gee had already completed basic development and was entering into initial production.[3]

In response, the original Project 3 team decided to end development, and re-purpose their work to provide long-range navigation on the oceans. This led to US Navy interest, and a series of experiments quickly demonstrated that systems using the basic Gee concept but operating at around 2 MHz would offer reasonable accuracy on the order of a few miles over distances on the order of 1,250 miles (2,010 km), at least at night when signals of this frequency range were able to skip off the ionosphere.[3] Rapid development followed, and a system covering the western Atlantic was operational in 1943. Additional stations followed, covering the European side, and then a massive expansion in the Pacific. By the end of the war there were 72 operational LORAN stations, and as many as 75,000 receivers. In 1958 the operation of the LORAN system was handed over to the US Coast Guard, which re-named the system "Loran-A", the lower-case name being introduced at that time.

LF LORAN[edit]

There are two ways to implement the timing measurements needed for a hyperbolic navigation system, pulse timing systems like Gee and LORAN-A, and phase-timing systems like the Decca Navigator System. The former requires sharp pulses of signal, and their accuracy is generally limited to how rapidly the pulses can be turned on and off, which is, in turn, a function of the carrier frequency. The second requires constant signals ("continuous wave") and is easy to use even at low frequencies, but is subject to an ambiguity in location that has to be determined using some other navigation method.

It was known from the start of the LORAN project that the same CRT displays that showed the LORAN pulses would also, when suitably magnified, show the individual waves of the intermediate frequency. This meant that pulse-matching could be used to get a rough fix, and then the operator could gain additional timing accuracy by lining up the individual waves within the pulse, like Decca. This could either be used to greatly increase the accuracy of LORAN, or alternately, offer similar accuracy using much lower carrier frequencies, and thus greatly extend range. This would require the transmitter stations to be synchronized both in time and phase, but much of this problem had been solved by Decca.

The long-range option was of considerable interest to the Coast Guard, who set up an experimental system known as LF LORAN in 1945. This operated at much lower frequencies than the original LORAN, 180 kHz, and required very long balloon-borne antennas. Testing was carried out throughout the year, including several long-distance flights as far as Brazil. The experimental system was then sent to Canada where it was used during Operation Muskox in the Arctic. Accuracy was found to be 150 feet (46 m) at 750 miles (1,210 km), a significant advance over LORAN. With the ending of Muskox it was decided to keep the system running under what became known as "Operation Musk Calf", run by a group consisting of the US Air Force, Royal Canadian Air Force, Royal Canadian Navy and Royal Corps of Signals. The system ran until September 1947.

This led to another major test series, this time by the newly-formed USAF, known as Operation Beetle. Beetle was located in the far north, on the Canada-Alaska border, and used new guy-stayed 625 feet (191 m) steel towers, replacing the earlier system's balloon-lofted cable antennas. The system became operational in 1948 and ran for two years until February 1950. Unfortunately the stations proved poorly sited, as the radio transmission over the permafrost was much shorter than expected and synchronization of the signals between the stations using groundwaves proved impossible. The tests also showed that the system was extremely difficult to use in practice; it was easy for the operator to select the wrong sections of the waveforms on their display, leading to significant real-world inaccuracy.

CYCLAN[edit]

In 1946 Sperry proposed a version of LF LORAN that would be entirely automated. In order to match the pulses and waves within them, their CYCLAN system would send out the same signal on two frequencies, LF LORAN's 180 kHz and again on 200 kHz.

LORAN-B and -C[edit]

During the 1950s, new electronic circuit designs allowed a continuous signal to be re-created out of short pulses. Using this technique, one can reconstruct a phase-coherent version of an original continuous signal from the pulses, a signal that will remain accurate over short periods of time. This was used in analog color televisions to extract the "color carrier" frequency, which was encoded into short bursts of signal outside the visual portion of the signal. This re-created carrier is then used to extract the color information from the following signal.

In the case of navigation systems, it allowed the receiver to re-create an original carrier frequency like the one used in Decca, while still sending pulsed information. This meant that one of the two pieces of information could be used for gross navigation, while the other could add additional accuracy. For instance, if one uses the generally highly-accurate Decca system of phase comparison for fine navigation, the pulse timing can be used as a secondary system to eliminate the ambiguity Decca suffered from. Additionally, it is energetically advantageous to send pulses, allowing much higher power transmitters to be used.

By the early 1950s a number of such projects were being developed. LORAN-B operated on the same frequencies as LORAN, which became "LORAN-A", but added phase-comparison to improve accuracy from miles to yards. LORAN-C was a similar development, but operating at much lower frequencies to further improve range. Ultimately LORAN-B would fail for a number of practical reasons, while LORAN-C proved itself and went into operation in 1957. The next year the system was handed over to the US Coast Guard.

Decline[edit]

In November 2009, the USCG announced that LORAN-C is not needed by the U.S. for maritime navigation. This decision left the fate of LORAN and eLORAN in the U.S. to the Secretary of the Department of Homeland Security.[4] Per a subsequent announcement, the U.S. Coast Guard, in accordance with the DHS Appropriations Act, terminated the transmission of all U.S. LORAN-C signals on 8 February 2010.[1] On 1 August 2010 the U.S. transmission of the Russian American signal was terminated,[1] and on 3 August 2010 all Canadian signals were shut down by the USCG and the CCG.[1][2]

Principle[edit]

A crude diagram of the LORAN principle—the difference between the time of reception of synchronized signals from radio stations A and B is constant along each hyperbolic curve; when demarcated on a map, such curves are known as "TD lines". "TD" stands for "Time Difference".

The navigational method provided by LORAN is based on measuring the time difference between the receipt of signals from a pair of radio transmitters.[5] A given constant time difference between the signals from the two stations can be represented by a hyperbolic line of position (LOP).

If the positions of the two synchronized stations are known, then the position of the receiver can be determined as being somewhere on a particular hyperbolic curve where the time difference between the received signals is constant. In ideal conditions, this is proportionally equivalent to the difference of the distances from the receiver to each of the two stations.

So a LORAN receiver which only receives two LORAN stations cannot fully fix its position—it only narrows it down to being somewhere on a curved line. Therefore the receiver must receive and calculate the time difference between a second pair of stations. This allows to be calculated a second hyperbolic line on which the receiver is located. Where these two lines cross is the location of the receiver.

In practice, one of the stations in the second pair also may be—and frequently is—in the first pair. This means signals must be received from at least three LORAN transmitters to pinpoint the receiver's location. By determining the intersection of the two hyperbolic curves identified by this method, a geographic fix can be determined.

LORAN method[edit]

LORAN pulse

In the case of LORAN, one station remains constant in each application of the principle, the primary, being paired up separately with two other secondary stations. Given two secondary stations, the time difference (TD) between the primary and first secondary identifies one curve, and the time difference between the primary and second secondary identifies another curve, the intersections of which will determine a geographic point in relation to the position of the three stations. These curves are referred to as TD lines.[6]

In practice, LORAN is implemented in integrated regional arrays, or chains, consisting of one primary station and at least two (but often more) secondary stations, with a uniform group repetition interval (GRI) defined in microseconds. The amount of time before transmitting the next set of pulses is defined by the distance between the start of transmission of primary to the next start of transmission of primary signal.

The secondary stations receive this pulse signal from the primary, then wait a preset number of milliseconds, known as the secondary coding delay, to transmit a response signal. In a given chain, each secondary's coding delay is different, allowing for separate identification of each secondary's signal. (In practice, however, modern LORAN receivers do not rely on this for secondary identification.)[citation needed]

LORAN chains (GRIs)[edit]

LORAN Station Malone, Malone, Florida Great Lakes chain (GRI 8970)/Southeast U.S. chain (GRI 7980)

Every LORAN chain in the world uses a unique Group Repetition Interval, the number of which, when multiplied by ten, gives how many microseconds pass between pulses from a given station in the chain. (In practice, the delays in many, but not all, chains are multiples of 100 microseconds.) LORAN chains are often referred to by this designation (e.g., GRI 9960, the designation for the LORAN chain serving the Northeast United States).[citation needed]

Due to the nature of hyperbolic curves, a particular combination of a primary and two secondary stations can possibly result in a "grid" where the grid lines intersect at shallow angles. For ideal positional accuracy, it is desirable to operate on a navigational grid where the grid lines are closer to right angles (orthogonal) to each other. As the receiver travels through a chain, a certain selection of secondaries whose TD lines initially formed a near-orthogonal grid can become a grid that is significantly skewed. As a result, the selection of one or both secondaries should be changed so that the TD lines of the new combination are closer to right angles. To allow this, nearly all chains provide at least three, and as many as five, secondaries.[citation needed]

LORAN charts[edit]

This nautical chart of New York Harbor includes LORAN-A TD lines. Note that the printed lines do not extend into inland waterway areas.

Where available, common marine nautical charts include visible representations of TD lines at regular intervals over water areas. The TD lines representing a given primary-secondary pairing are printed with distinct colors, and note the specific time difference indicated by each line. On a nautical chart, the denotation for each Line of Position from a receiver, relative to axis and color, can be found at the bottom of the chart. The color on official charts for stations and the timed-lines of position follow no specific conformance for the purpose of the International Hydrographic Organization (IHO). However, local chart producers may color these in a specific conformance to their standard. Always consult the chart notes, administrations Chart1 reference, and information given on the chart for the most accurate information regarding surveys, datum, and reliability.

There are three major factors when considering signal delay and propagation in relation to LORAN-C:

  1. Primary Phase Factor (PF) – This allows for the fact that the speed of the propagated signal in the atmosphere is slightly lower than in a vacuum.
  2. Secondary Phase Factor (SF) – This allows for the fact that the speed of propagation of the signal is slowed when traveling over the seawater because of the greater conductivity of seawater compared to land.
  3. Additional Secondary Factors (ASF) – Because LORAN-C transmitters are mainly land based, the signal will travel partly over land and partly over seawater. ASF may be treated as land and water segments, each with a uniform conductivity depending on whether the path is over land or water.

The chart notes should indicate whether ASF corrections have been made (Canadian Hydrographic Service (CHS) charts, for example, include them). Otherwise, the appropriate correction factors must be obtained before use.

Due to interference and propagation issues suffered from land features and artificial structures such as tall buildings, the accuracy of the LORAN signal can be degraded considerably in inland areas (see Limitations). As a result, nautical charts will not show TD lines in those areas, to prevent reliance on LORAN-C for navigation.

Traditional LORAN receivers display the time difference between each pairing of the primary and one of the two selected secondary stations, which is then used to find the appropriate TD line on the chart. Modern LORAN receivers display latitude and longitude coordinates instead of time differences, and, with the advent of time difference comparison and electronics, provide improved accuracy and better position fixing, allowing the observer to plot their position on a nautical chart more easily. When using such coordinates, the datum used by the receiver (usually WGS84) must match that of the chart, or manual conversion calculations must be performed before the coordinates can be used.

Timing and synchronization[edit]

Cesium atomic clocks

Each LORAN station is equipped with a suite of specialized equipment to generate the precisely timed signals used to modulate / drive the transmitting equipment. Up to three commercial cesium atomic clocks are used to generate 5 MHz and pulse per second (or 1 Hz) signals that are used by timing equipment to generate the various GRI-dependent drive signals for the transmitting equipment.

While each U.S.-operated LORAN station is supposed to be synchronized to within 100 ns of UTC, the actual accuracy achieved as of 1994 was within 500 ns.[7]

Transmitters and antennas[edit]

LORAN transmitter bank

LORAN-C transmitters operate at peak powers of 100–4,000 kilowatts, comparable to longwave broadcasting stations. Most use 190–220 metre tall mast radiators, insulated from ground. The masts are inductively lengthened and fed by a loading coil (see: electrical lengthening). A well known-example of a station using such an antenna is Rantum. Free-standing tower radiators in this height range are also used[clarification needed]. Carolina Beach uses a free-standing antenna tower. Some LORAN-C transmitters with output powers of 1,000 kW and higher used supertall 412 metre mast radiators (see below). Other high power LORAN-C stations, like George, used four T-antennas mounted on four guyed masts arranged in a square.

All LORAN-C antennas are designed to radiate an omnidirectional pattern. Unlike longwave broadcasting stations, LORAN-C stations cannot use backup antennas because the exact position of the antenna is a part of the navigation calculation. The slightly different physical location of a backup antenna would produce Lines of Position different from those of the primary antenna.

Limitations[edit]

LORAN suffers from electronic effects of weather and the ionospheric effects of sunrise and sunset. The most accurate signal is the groundwave that follows the Earth's surface, ideally over seawater. At night the indirect skywave, bent back to the surface by the ionosphere, is a problem as multiple signals may arrive via different paths (multipath interference). The ionosphere's reaction to sunrise and sunset accounts for the particular disturbance during those periods. Magnetic storms have serious effects as with any radio based system.

LORAN uses ground based transmitters that only cover certain regions. Coverage is quite good in North America, Europe, and the Pacific Rim.

The absolute accuracy of LORAN-C varies from 0.10 to 0.25 nmi (185 to 463 m). Repeatable accuracy is much greater, typically from 60 to 300 ft (18 to 91 m).[8]

LORAN-A and other systems[edit]

LORAN-A was a less accurate system operating in the upper mediumwave frequency band prior to deployment of the more accurate LORAN-C system.[9] For LORAN-A the transmission frequencies 1750 kHz, 1850 kHz, 1900 kHz and 1950 kHz were used, shared with the 1800–2000 kHz amateur 160-meter band. LORAN-A continued in operation partly due to the economy of the receivers and widespread use in civilian recreational and commercial navigation. LORAN-B was a phase comparison variation of LORAN-A while LORAN-D was a short-range tactical system designed for USAF bombers. The unofficial "LORAN-F" was a drone control system. None of these went much beyond the experimental stage. An external link to them is listed below.

LORAN-A was used in the Vietnam War for navigation by large United States aircraft (C-124, C-130, C-97, C-123, HU-16, etc.). A common airborne receiver of that era was the R-65/APN-9 which combined the receiver and cathode ray tube (CRT) indicator into a single relatively lightweight unit replacing the two larger, separate receiver and indicator units which composed the predecessor APN-4 system. The APN-9 and APN-4 systems found wide post–World War II use on fishing vessels in the U.S. They were cheap, accurate and plentiful. The main drawback for use on boats was their need for aircraft power, 115 VAC at 400 Hz. This was solved initially by the use of rotary converters, typically 28 VDC input and 115 VAC output at 400 Hz. The inverters were large, noisy and required significant power. In the 1960s, several firms such as Topaz and Linear Systems marketed solid state inverters specifically designed for these surplus LORAN-A sets. The availability of solid state inverters that used 12 VDC input opened up the surplus LORAN-A sets for use on much smaller vessels which typically did not have the 24-28 VDC systems found on larger vessels. The solid state inverters were very power efficient and widely replaced the more trouble prone rotary inverters.

LORAN-A saved many lives by allowing offshore boats in distress to give accurate position reports. It also guided many boats whose owners could not afford radar safely into fog bound harbors or around treacherous offshore reefs. The low price of surplus LORAN-A receivers (often under $150) meant that owners of many small fishing vessels could afford this equipment, thus greatly enhancing safety. Surplus LORAN-A equipment, which was common on commercial fishing boats, was rarely seen on yachts. The unrefined cosmetic appearance of the surplus equipment was probably a deciding factor.

Pan American World Airways used APN 9s in early Boeing 707 operations. World War II surplus APN-9 looked out of place in the modern 707 cockpit, but was needed. There is an R65A APN-9 set displayed in the museum at San Francisco International Airport, painted gold. It was a retirement gift to an ex Pan Am captain.

An elusive final variant of the APN 9 set was the APN 9A. A USAF technical manual (with photographs and schematics) shows that it had the same case as the APN-9 but a radically different front panel and internal circuitry on the non-RF portions. The APN-9A had vacuum tube flipflop digital divider circuits so that TDs (time delays) between the primary and secondary signal could be selected on front panel rotary decade switches. The older APN-9 set required the user to perform a visual count of crystal oscillator timing marker pips on the CRT and add them up to get a TD. The APN 9A did not make it into widespread military use, if it was used at all, but it did exist and represented a big advance in military LORAN-A receiver technology.

In the 1970s one US company, SRD Labs in Campbell, California, made modern LORAN-A sets including one that was completely automatic with a digital TD readout on the CRT, and autotracking so that TDs were continuously updated. Other SRD models required the user to manually align the primary and secondary signals on the CRT and then a phase locked loop would keep them lined up and provide updated TD readouts thereafter. These SRD LORAN-A sets would track only one pair of stations, providing just one LOP (line of position). For a continuously updated position (two TDs giving intersecting LOPs) rather than just a single LOP, two sets were necessary.

LORAN-A was terminated in the United States on 31 December 1980 and the restrictions on amateur radio use of the 160-meter band were lifted.

Long after LORAN-A broadcasts were terminated, commercial fishermen still referred to old LORAN-A TDs, e.g., "I am on the 4100 [microsecond] line in 35 fathoms", referring to a position outside Bodega Bay. Many LORAN-C sets incorporated LORAN A TD converters so that a LORAN-C set could be used to navigate to a LORAN-A TD defined line or position.

LORAN Data Channel (LDC)[edit]

LORAN Data Channel (LDC) is a project underway between the FAA and USCG to send low bit rate data using the LORAN system. Messages to be sent include station identification, absolute time, and position correction messages. In 2001, data similar to Wide Area Augmentation System (WAAS) GPS correction messages were sent as part of a test of the Alaskan LORAN chain. As of November 2005, test messages using LDC were being broadcast from several U.S. LORAN stations.[citation needed]

In recent years, LORAN-C has been used in Europe to send differential GPS and other messages, employing a similar method of transmission known as EUROFIX.[citation needed]

A system called SPS (Saudi Positioning System), similar to EUROFIX, is in use in Saudi Arabia.[10] GPS differential corrections and GPS integrity information are added to the LORAN signal. A combined GPS/LORAN receiver is used, and if a GPS fix is not available it automatically switches over to LORAN.

The future of LORAN[edit]

As LORAN systems are government maintained and operated, their continued existence is subject to public policy. With the evolution of other electronic navigation systems, such as satellite navigation systems, funding for existing systems is not always assured.

Critics, who have called for the elimination of the system, state that the LORAN system has too few users, lacks cost-effectiveness, and that GNSS signals are superior to LORAN.[citation needed] Supporters of continued and improved LORAN operation note that LORAN uses a strong signal, which is difficult to jam, and that LORAN is an independent, dissimilar, and complementary system to other forms of electronic navigation, which helps ensure availability of navigation signals.[11][12]

On 26 February 2009, the U.S. Office of Management and Budget released the first blueprint for the Financial Year 2010 budget.[13] This document identified the LORAN-C system as “outdated” and supported its termination at an estimated savings of $36 million in 2010 and $190 million over five years.

On 21 April 2009 the U.S. Senate Committee on Commerce, Science and Transportation and the Committee on Homeland Security and Governmental Affairs released inputs to the FY 2010 Concurrent Budget Resolution with backing for the continued support for the LORAN system, acknowledging the investment already made in infrastructure upgrades and recognizing the studies performed and multi-departmental conclusion that eLORAN is the best backup to GPS.

Senator Jay Rockefeller, Chairman of the Committee on Commerce, Science and Transportation, wrote that the committee recognized the priority in "Maintaining LORAN-C while transitioning to eLORAN" as means of enhancing the homeland security, marine safety and environmental protection missions of the Coast Guard.

Senator Collins, the ranking member on the Committee on Homeland Security and Governmental Affairs wrote that the President's budget overview proposal to terminate the LORAN-C system is inconsistent with the recent investments, recognized studies and the mission of the U.S. Coast Guard. The committee also recognizes the $160 million investment already made toward upgrading the LORAN-C system to support the full deployment of eLORAN.

Further, the Committees also recognize the many studies which evaluated GPS backup systems and concluded both the need to back up GPS and identified eLORAN as the best and most viable backup. "This proposal is inconsistent with the recently released (January 2009) Federal Radionavigation Plan (FRP), which was jointly prepared by DHS and the Departments of Defense (DOD) and Transportation (DOT). The FRP proposed the eLORAN program to serve as a Position, Navigation and Timing (PNT) backup to GPS (Global Positioning System)."

On 7 May 2009, President Barack Obama proposed cutting funding (approx. $35 million/year) for LORAN, citing its redundancy alongside GPS.[14] In regard to the pending Congressional bill, H.R. 2892, it was subsequently announced that "[t]he Administration supports the Committee's aim to achieve an orderly termination through a phased decommissioning beginning in January 2010, and the requirement that certifications be provided to document that the LORAN-C termination will not impair maritime safety or the development of possible GPS backup capabilities or needs."[15]

Also on 7 May 2009, the U.S. General Accounting Office (GAO), the investigative arm of Congress, released a report citing the very real potential for the GPS system to degrade or fail in light of program delays which have resulted in scheduled GPS satellite launches slipping by up to three years.[16]

On 12 May 2009 the March 2007 Independent Assessment Team (IAT) report on LORAN was released to the public. In its report the ITA stated that it "unanimously recommends that the U.S. government complete the eLORAN upgrade and commit to eLORAN as the national backup to GPS for 20 years." The release of the report followed an extensive Freedom Of Information Act (FOIA) battle waged by industry representatives against the federal government. Originally completed 20 March 2007 and presented to the co-sponsoring Department of Transportation and Department of Homeland Security (DHS) Executive Committees, the report carefully considered existing navigation systems, including GPS. The unanimous recommendation for keeping the LORAN system and upgrading to eLORAN was based on the team's conclusion that LORAN is operational, deployed and sufficiently accurate to supplement GPS. The team also concluded that the cost to decommission the LORAN system would exceed the cost of deploying eLORAN, thus negating any stated savings as offered by the Obama administration and revealing the vulnerability of the U.S. to GPS disruption.[17]

In November 2009, the U.S. Coast Guard announced that the LORAN-C stations under its control would be closed down for budgetary reasons after 4 January 2010 provided the Secretary of the Department of Homeland Security certified that LORAN is not needed as a backup for GPS.[18]

On 7 January 2010, Homeland Security published a notice of the permanent discontinuation of LORAN-C operation. Effective 2000 UTC 8 February 2010, the United States Coast Guard terminated all operation and broadcast of LORAN-C signals in the USA. The U.S. Coast Guard transmission of the Russian American CHAYKA signal was terminated on 1 August 2010. The transmission of Canadian LORAN-C signals was terminated on 3 August 2010.[19]

eLORAN[edit]

With the perceived vulnerability of GNSS systems,[20] and their own propagation and reception limitations, renewed interest in LORAN applications and development has appeared.[21] Enhanced LORAN, also known as eLORAN or E-LORAN, comprises an advancement in receiver design and transmission characteristics which increase the accuracy and usefulness of traditional LORAN. With reported accuracy as good as ± 8 meters,[22] the system becomes competitive with unenhanced GPS. eLORAN also includes additional pulses which can transmit auxiliary data such as DGPS corrections. eLORAN receivers now use "all in view" reception, incorporating signals from all stations in range, not solely those from a single GRI, incorporating time signals and other data from up to 40 stations. These enhancements in LORAN make it adequate as a substitute for scenarios where GPS is unavailable or degraded.[23]

United Kingdom eLORAN implementation[edit]

On 31 May 2007, the UK Department for Transport (DfT), via the General Lighthouse Authorities (GLA), awarded a 15-year contract to provide a state-of-the-art enhanced LORAN (eLORAN) service to improve the safety of mariners in the UK and Western Europe. The service contract will operate in two phases, with development work and further focus for European agreement on eLORAN service provision from 2007 through 2010, and full operation of the eLORAN service from 2010 through 2022. The first eLORAN transmitter is situated at Anthorn radio station Cumbria, UK, and operated by Babcock Comms, which is part of the Babcock Group PLC.[24]

eLORAN: The UK government has granted approval for seven differential eLoran ship-positioning technology stations to be built along the south and east coasts of the UK to help counter the threat of jamming of global positioning systems. They are set to reach initial operational capability by summer 2014.[25]

List of LORAN-C transmitters[edit]

Map of LORAN stations.

A list of LORAN-C transmitters. Stations with an antenna tower taller than 300 metres (984 feet) are shown in bold.

Station Country Chain Coordinates Remarks
Afif Saudi Arabia Saudi Arabia South (GRI 7030)
Saudi Arabia North (GRI 8830)
23°48′36.66″N 42°51′18.17″E / 23.8101833°N 42.8550472°E / 23.8101833; 42.8550472 (Afif – 7030-X / 8830-M) 400 kW
Al Khamasin Saudi Arabia Saudi Arabia South (GRI 7030)
Saudi Arabia North (GRI 8830)
20°28′2.34″N 44°34′51.9″E / 20.4673167°N 44.581083°E / 20.4673167; 44.581083 (Al Khamasin – 7030-M / 8830-X)
Al Muwassam Saudi Arabia Saudi Arabia South (GRI 7030)
Saudi Arabia North (GRI 8830)
16°25′56.87″N 42°48′6.21″E / 16.4324639°N 42.8017250°E / 16.4324639; 42.8017250 (Al Muwassam – 7030-Z / 8830-Z)
Angissq Greenland Shutdown on 31 December 1994 59°59′17.348″N 45°10′26.91″W / 59.98815222°N 45.1741417°W / 59.98815222; -45.1741417 (Angissq – Shut down) used until 27 July 1964 a 411.48 metre tower
Anthorn UK Lessay (GRI 6731) 54°54′41.949″N 3°16′42.58″W / 54.91165250°N 3.2784944°W / 54.91165250; -3.2784944 (Anthorn – 6731-Y) replacement for transmitter Rugby[26]
Ash Shaykh Humayd Saudi Arabia Saudi Arabia South (GRI 7030)
Saudi Arabia North (GRI 8830)
28°9′15.87″N 34°45′41.36″E / 28.1544083°N 34.7614889°E / 28.1544083; 34.7614889 (Ash Shaykh Humayd – 7030-Y / 8830-Y)
Attu Island United States North Pacific (GRI 9990)
Russian-American (GRI 5980)
52°49′44″N 173°10′49.7″E / 52.82889°N 173.180472°E / 52.82889; 173.180472 (Attu – 5980-W / 9990-X) demolished in August 2010
Balasore India Calcutta (GRI 5543) 21°29′11.02″N 86°55′9.66″E / 21.4863944°N 86.9193500°E / 21.4863944; 86.9193500 (Balasore - 5543-M)
Barrigada Guam shut down 13°27′50.16″N 144°49′33.4″E / 13.4639333°N 144.825944°E / 13.4639333; 144.825944 (Barrigada - Shut down)
Baudette United States North Central U.S. (GRI 8290)
Great Lakes (GRI 8970)
48°36′49.947″N 94°33′17.91″W / 48.61387417°N 94.5549750°W / 48.61387417; -94.5549750 (Baudette - 8290-W / 8970-Y)
Berlevåg Norway Bø (GRI 7001) 70°50′43.07″N 29°12′16.04″E / 70.8452972°N 29.2044556°E / 70.8452972; 29.2044556 (Berlevåg - 7001-Y)
Bilimora India Bombay (GRI 6042) 20°45′42.036″N 73°02′14.48″E / 20.76167667°N 73.0373556°E / 20.76167667; 73.0373556 (Bilimora - 6042-X)
Boise City United States Great Lakes (GRI 8970)
South Central U.S. (GRI 9610)
36°30′20.75″N 102°53′59.4″W / 36.5057639°N 102.899833°W / 36.5057639; -102.899833 (Boise City - 8970-Z / 9610-M)
Bø, Vesterålen Norway Bø (GRI 7001)
Eiði (GRI 9007)
68°38′06.216″N 14°27′47.35″E / 68.63506000°N 14.4631528°E / 68.63506000; 14.4631528 (Bø - 7001-M / 9007-X)
Cambridge Bay Canada shut down 69°06′52.840″N 105°00′55.95″W / 69.11467778°N 105.0155417°W / 69.11467778; -105.0155417 (Cambridge Bay - Shut down) free-standing lattice tower, used as NDB
Cape Race Canada Canadian East Coast (GRI 5930)
Newfoundland East Coast (GRI 7270)
46°46′32.74″N 53°10′28.66″W / 46.7757611°N 53.1746278°W / 46.7757611; -53.1746278 (Cape Race - 5930-Y / 7270-W) used a 411.48 metre tall tower until 2 February 1993, uses now a 260.3 metre tall tower
Caribou, Maine United States Canadian East Coast (GRI 5930)
Northeast U.S. (GRI 9960)
46°48′27.305″N 67°55′37.15″W / 46.80758472°N 67.9269861°W / 46.80758472; -67.9269861 (Caribou - 5930-M / 9960-W)
Carolina Beach United States Southeast U.S. (GRI 7980)
Northeast US (GRI 9960)
34°03′46.208″N 77°54′46.10″W / 34.06283556°N 77.9128056°W / 34.06283556; -77.9128056 (Carolina Beach - 7980-Z / 9960-Y)
Chongzuo China China South Sea (GRI 6780) 22°32′35.8″N 107°13′19″E / 22.543278°N 107.22194°E / 22.543278; 107.22194 (Chongzuo - 6780-Y)
Comfort Cove Canada Newfoundland East Coast (GRI 7270) 49°19′53.65″N 54°51′43.2″W / 49.3315694°N 54.862000°W / 49.3315694; -54.862000 (Comfort Cove - 7270-M)
Dana United States Great Lakes (GRI 8970)
Northeast US (GRI 9960)
39°51′7.64″N 87°29′10.71″W / 39.8521222°N 87.4863083°W / 39.8521222; -87.4863083 (Dana - 8970-M / 9960-Z)
Dhrangadhra India Bombay (GRI 6042) 23°0′16.2″N 71°31′37.64″E / 23.004500°N 71.5271222°E / 23.004500; 71.5271222 (Dhrangadhra - 6042-M)
Diamond Harbor India Calcutta (GRI 5543) 22°10′20.42″N 88°12′15.8″E / 22.1723389°N 88.204389°E / 22.1723389; 88.204389 (Diamond Harbor - 5543-W)
Eiði Faroe Islands Eiði (GRI 9007) 62°17′59.69″N 7°4′25.59″W / 62.2999139°N 7.0737750°W / 62.2999139; -7.0737750 (Eiði - 9007-M)
Estartit Spain Mediterranean Sea (GRI 7990)
(Shut down)
42°3′36.63″N 3°12′16.08″E / 42.0601750°N 3.2044667°E / 42.0601750; 3.2044667 (Estartit - Shut down)
Fallon United States U.S. West Coast (GRI 9940) 39°33′6.77″N 118°49′55.6″W / 39.5518806°N 118.832111°W / 39.5518806; -118.832111 (Fallon - 9940-M)
Fox Harbour Canada Canadian East Coast (GRI 5930)
Newfoundland East Coast (GRI 7270)
52°22′35.29″N 55°42′28.68″W / 52.3764694°N 55.7079667°W / 52.3764694; -55.7079667 (Fox Harbour - 5930-Z / 7270-X)
George United States Canadian West Coast (GRI 5990) 47°03′48.096″N 119°44′38.97″W / 47.06336000°N 119.7441583°W / 47.06336000; -119.7441583 (George - 5990-Y / 9940-W)
Gesashi Japan North West Pacific (GRI 8930)
East Asia (GRI 9930)
26°36′25.09″N 128°8′56.94″E / 26.6069694°N 128.1491500°E / 26.6069694; 128.1491500 (Gesashi - 8930-W / 9930-X)
Gillette United States North Central U.S. (GRI 8290)
South Central U.S. (GRI 9610)
44°0′11.21″N 105°37′24″W / 44.0031139°N 105.62333°W / 44.0031139; -105.62333 (Gillette - 8290-X / 9610-V)
Grangeville United States Southeast U.S. (GRI 7980)
South Central U.S. (GRI 9610)
30°43′33.24″N 90°49′43.01″W / 30.7259000°N 90.8286139°W / 30.7259000; -90.8286139 (Grangeville - 7980-W / 9610-Z)
Havre United States North Central U.S. (GRI 8290) 48°44′38.58″N 109°58′53.3″W / 48.7440500°N 109.981472°W / 48.7440500; -109.981472 (Havre - 8290-M)
Hellissandur Iceland shut down on 31 December 1994 64°54′14.793″N 23°54′47.83″W / 64.90410917°N 23.9132861°W / 64.90410917; -23.9132861 (Hellissandur - Shut down) 411.48 metre tall tower, now used for longwave broadcasting of RÚV on 189 kHz
Helong China China North Sea (GRI 7430) 42°43′11″N 129°6′27.07″E / 42.71972°N 129.1075194°E / 42.71972; 129.1075194 (Helong - 7430-Y)
Hexian China China South Sea (GRI 6780) 23°58′3.21″N 111°43′9.78″E / 23.9675583°N 111.7193833°E / 23.9675583; 111.7193833 (Hexian - 6780-M)
Iwo Jima Japan shut down in September 1993, dismantled 24°48′26.262″N 141°19′34.76″E / 24.80729500°N 141.3263222°E / 24.80729500; 141.3263222 (Iwo Jima - Shut down) used a 411.48 metre tall tower
Jan Mayen Norway Bø (GRI 7001)
Ejde (GRI 9007)
70°54′51.478″N 8°43′56.52″W / 70.91429944°N 8.7323667°W / 70.91429944; -8.7323667 (Jan Mayen - 7001-X / 9007-W)
Johnston Island United States shut-down 16°44′43.82″N 169°30′30.9″W / 16.7455056°N 169.508583°W / 16.7455056; -169.508583 (Johnston Island - Shut down)
Jupiter United States Southeast U.S. (GRI 7980) 27°1′58.49″N 80°6′52.83″W / 27.0329139°N 80.1146750°W / 27.0329139; -80.1146750 (Jupiter - 7980-Y)
Kargaburun Turkey Mediterranean Sea (GRI 7990)
(Shut down)
40°58′20.51″N 27°52′1.89″E / 40.9723639°N 27.8671917°E / 40.9723639; 27.8671917 (Kargaburan - Shut down)
Kwang Ju South Korea East Asia (GRI 9930) 35°2′23.69″N 126°32′27.2″E / 35.0399139°N 126.540889°E / 35.0399139; 126.540889 (Kwang Ju - 9930-W)
Lampedusa Italy Mediterranean Sea (GRI 7990)
(Shut down)
35°31′22.11″N 12°31′31.06″E / 35.5228083°N 12.5252944°E / 35.5228083; 12.5252944 (Lampedusa - Shut down)
Las Cruces United States South Central U.S. (GRI 9610) 32°4′18.1″N 106°52′4.32″W / 32.071694°N 106.8678667°W / 32.071694; -106.8678667 (Las Cruces - 9610-X)
Lessay France Lessay (GRI 6731)
Sylt (GRI 7499)
49°8′55.27″N 1°30′17.03″W / 49.1486861°N 1.5047306°W / 49.1486861; -1.5047306 (Lessay - 6731-M / 7499-X)
Loop Head Ireland Lessay (GRI 6731)
Eiði (GRI 9007)
(Never built) 250 kW
Malone United States Southeast U.S. (GRI 7980)
Great Lakes (GRI 8970)
30°59′38.87″N 85°10′8.71″W / 30.9941306°N 85.1690861°W / 30.9941306; -85.1690861 (Malone - 7980-M / 8970-W)
Middletown United States U.S. West Coast (GRI 9940) 38°46′57.12″N 122°29′43.9″W / 38.7825333°N 122.495528°W / 38.7825333; -122.495528 (Middletown - 9940-X)
Minamitorishima Japan North West Pacific (GRI 8930) 24°17′8.79″N 153°58′52.2″E / 24.2857750°N 153.981167°E / 24.2857750; 153.981167 (Minamitorishima - 8930-X) used until 1985 a 411.48 metre tall tower
Nantucket United States Canadian East Coast (GRI 5930)
Northeast U.S. (GRI 9960)
41°15′12.42″N 69°58′38.73″W / 41.2534500°N 69.9774250°W / 41.2534500; -69.9774250 (Nantucket - 5930-X / 9960-X)
Narrow Cape United States Gulf of Alaska (GRI 7960)
North Pacific (GRI 9990)
57°26′20.5″N 152°22′10.2″W / 57.439028°N 152.369500°W / 57.439028; -152.369500 (Narrow Cape - 7960-X / 9990-Z)
Niijima Japan North West Pacific (GRI 8930)
East Asia (GRI 9930)
34°24′12.06″N 139°16′19.4″E / 34.4033500°N 139.272056°E / 34.4033500; 139.272056 (Niijima - 8930-M / 9930-Y)
Patpur India Calcutta (GRI 5543) 20°26′50.627″N 85°49′38.67″E / 20.44739639°N 85.8274083°E / 20.44739639; 85.8274083 (Patpur - 5543-X)
Pohang South Korea North West Pacific (GRI 8930)
East Asia (GRI 9930)
36°11′5.33″N 129°20′27.4″E / 36.1848139°N 129.340944°E / 36.1848139; 129.340944 (Pohang - 8930-Z / 9930-M)
Port Clarence United States Gulf of Alaska (GRI 7960)
North Pacific (GRI 9990)
65°14′40.372″N 166°53′11.996″W / 65.24454778°N 166.88666556°W / 65.24454778; -166.88666556 (Port Clarence - 7960-Z / 9990-Y) uses a 411.48 metre tall tower Demolished 28 April 2010 [27]
Port Hardy Canada Canadian West Coast (GRI 5990) 50°36′29.830″N 127°21′28.48″W / 50.60828611°N 127.3579111°W / 50.60828611; -127.3579111 (Port Hardy - 5990-Z)
Rantum Germany Lessay (GRI 6731)
Sylt (GRI 7499)
54°48′29.94″N 8°17′36.9″E / 54.8083167°N 8.293583°E / 54.8083167; 8.293583 (Sylt - 6731-Z / 7499-M)
Raymondville United States Southeast U.S. (GRI 7980)
South Central U.S. (GRI 9610)
26°31′55.17″N 97°49′59.52″W / 26.5319917°N 97.8332000°W / 26.5319917; -97.8332000 (Raymondville - 7980-X / 9610-Y)
Raoping China China South Sea (GRI 6780)
China East Sea (GRI 8390)
23°43′26.02″N 116°53′44.7″E / 23.7238944°N 116.895750°E / 23.7238944; 116.895750 (Raoping - 6780-X / 8390-X)
Rongcheng China China North Sea (GRI 7430)
China East Sea (GRI 8390)
37°03′51.765″N 122°19′25.95″E / 37.06437917°N 122.3238750°E / 37.06437917; 122.3238750 (Rongcheng - 7430-M / 8390-Y)
Rugby UK Experimental (GRI 6731)
Shut down at the end of July 2007
52°21′57.893″N 1°11′27.39″W / 52.36608139°N 1.1909417°W / 52.36608139; -1.1909417 (Rugby - Shut Down)
Saint Paul United States North Pacific (GRI 9990) 57°9′12.35″N 170°15′6.06″W / 57.1534306°N 170.2516833°W / 57.1534306; -170.2516833 (Saint Paul - 9990-M)
Salwa Saudi Arabia Saudi Arabia South (GRI 7030)
Saudi Arabia North (GRI 8830)
24°50′1.46″N 50°34′12.54″E / 24.8337389°N 50.5701500°E / 24.8337389; 50.5701500 (Salwa - 7030-W / 8830-W)
Searchlight United States South Central U.S. (GRI 9610)
U.S. West Coast (GRI 9940)
35°19′18.305″N 114°48′16.88″W / 35.32175139°N 114.8046889°W / 35.32175139; -114.8046889 (Searchlight - 9610-W / 9940-Y)
Sellia Marina Italy Mediterranean Sea (GRI 7990); shut down 38°52′20.72″N 16°43′6.27″E / 38.8724222°N 16.7184083°E / 38.8724222; 16.7184083 (Sellia Marina - Shut down)
Seneca United States Great Lakes (GRI 8970)
Northeast U.S. (GRI 9960)
42°42′50.716″N 76°49′33.30″W / 42.71408778°N 76.8259167°W / 42.71408778; -76.8259167 (Seneca - 8970-X / 9960-M)
Shoal Cove United States Canadian West Coast (GRI 5990)
Gulf of Alaska (GRI 7960)
55°26′20.940″N 131°15′19.09″W / 55.43915000°N 131.2553028°W / 55.43915000; -131.2553028 (Shoal Cove - 5990-X / 7960-Y)
Soustons France Lessay (GRI 6731) 43°44′23.21″N 1°22′49.63″W / 43.7397806°N 1.3804528°W / 43.7397806; -1.3804528 (Soustons - 6731-X)
Tok United States Gulf of Alaska (GRI 7960) 63°19′42.884″N 142°48′31.34″W / 63.32857889°N 142.8087056°W / 63.32857889; -142.8087056 (Tok - 7960-M)
Tokachibuto Japan Eastern Russia Chayka (GRI 7950)
North West Pacific (GRI 8930)
42°44′37.2″N 143°43′10.5″E / 42.743667°N 143.719583°E / 42.743667; 143.719583 (Tokachibuto - 8930-Y)
Upolo Point United States Shut down 20°14′51.12″N 155°53′4.34″W / 20.2475333°N 155.8845389°W / 20.2475333; -155.8845389 (Upolo Point - Shut Down)
Værlandet Norway Sylt (GRI 7499)
Ejde (GRI 9007)
61°17′49.49″N 4°41′47.05″E / 61.2970806°N 4.6964028°E / 61.2970806; 4.6964028 (Værlandet - 7499-Y / 9007-Y)
Veraval India Bombay (GRI 6042) 20°57′09.316″N 70°20′11.73″E / 20.95258778°N 70.3365917°E / 20.95258778; 70.3365917 (Veraval - 6042-W)
Williams Lake Canada Canadian West Coast (GRI 5990)
North Central U.S. (GRI 8290)
51°57′58.78″N 122°22′1.55″W / 51.9663278°N 122.3670972°W / 51.9663278; -122.3670972 (Williams Lake - 5990-M / 8290-Y)
Xuancheng China China North Sea (GRI 7430)
China East Sea (GRI 8390)
31°4′8.3″N 118°53′8.78″E / 31.068972°N 118.8857722°E / 31.068972; 118.8857722 (Xuancheng - 7430-X / 8390-M)
Yap Micronesia shut down in 1987, dismantled 9°32′44.76″N 138°9′53.48″E / 9.5457667°N 138.1648556°E / 9.5457667; 138.1648556 (Yap - Shut down) used a 304.8 metre tall tower

See also[edit]

References[edit]

Notes
  1. ^ The original system was known as LORAN, a short-form for LOng RAnge Navigation. Operation of the system, and the newly introduced LORAN-C system, were handed to the Coast Guard in 1958. They took the time to retroactively change the name of the original system to Loran-A, and used lower-case naming from then on. See Gatterer, p. xi.
Citations
  1. ^ a b c d "LORAN-C General Information". United States Coast Guard. Retrieved 4 August 2010. 
  2. ^ a b "Termination of the Loran-C Service". notmar.gc.ca. Retrieved 4 August 2010.  (for access click on "I have read..." and "Accept")
  3. ^ a b c Halford, Davidson and Waldschmitt, "History of LORAN", MIT Radiation Laboratory, pp. 19-23.
  4. ^ Senate committee letter
  5. ^ Appleyard, S.F.; Linford, R.S. and Yarwood, P.J. (1988). Marine Electronic Navigation (2nd Edition). Routledge & Kegan Paul. pp. 77–83. ISBN 0-7102-1271-2. 
  6. ^ The American Practical Navigator, An Epitome of Navigation, page 173
  7. ^ "Chapter 2 ̣– LORAN-C Transmissions". Specification of the Transmitted LORAN-C Signal / COMDTINST M16562.4A. U.S. Coast Guard. 1994. pp. 6, 7. Retrieved 4 September 2012. 
  8. ^ COMDTPUB P16562.6, "LORAN-C Users Handbook", 1992
  9. ^ Jerry Proc, VE3FAB (26 November 2007). "LORAN A". Retrieved 28 May 2009. [dead link]
  10. ^ "A New Navigation Positioning System run by Saudi Ports Authority". Saudi Ports Authority. 2006. Retrieved 21 January 2011. 
  11. ^ "Enhanced Loran (eloran) Definition Document". International Loran Association. 16 October 2007. Retrieved 18 July 2010. 
  12. ^ "GPS back-up 'needs more research' ". bbc.co.uk, 20 June 2008, Retrieved 5 October 2010
  13. ^ Office of Management and Budget. ( www.budget.gov), "A New Era of Responsibility Renewing America's Promise" The FY 2010 Budget, Department of Homeland Security Section, page 72
  14. ^ Obama: Budget cuts add up to 'real money'
  15. ^ "H.R. 2892--Department of Homeland Security Appropriations Act, 2010". C-SPAN.org. 8 July 2009. Retrieved 10 August 2009. 
  16. ^ http://www.gao.gov/products/GAO-09-670T
  17. ^ http://sidt.gpsworld.com/gpssidt/article/articleDetail.jsp?id=597861
  18. ^ "USCG LORAN Program Manager release, Nov. 2009". 31 May 2007. Retrieved 28 November 2009. 
  19. ^ http://www.navcen.uscg.gov/?pageName=loranMain
  20. ^ http://news.bbc.co.uk/2/hi/science/nature/8533157.stm
  21. ^ "GPS vulnerable to hacker attacks". BBC News. 23 February 2010. Retrieved 11 May 2010. 
  22. ^ http://www.aviationtoday.com/av/commercial/GPS-Backup-Is-eLoran-the-Answer_76148.html Template:Date=April 2012
  23. ^ Press office (7 February 2008). "Statement from DHS press secretary Laura Keehhner on the adoption of national backup system to GPS" (PDF). press release. United States Department of Homeland Security. Retrieved 10 January 2013. 
  24. ^ "The GLAs award a 15-year eLORAN contract to Babcock Communications". Trinity House. 31 May 2007. Retrieved 27 May 2010. 
  25. ^ Nautilus International Newspaper August 2013
  26. ^ "Electronic Position Fixing System" (– Scholar search). Admiralty Notices to Mariners (United Kingdom Hydrographic Office) (26/07). 28 June 2007. Archived from the original on 24 June 2008. Retrieved 19 January 2008. [dead link]
  27. ^ http://coastguardnews.com/video-loran-station-port-clarence-tower-demolition/2010/05/01/
Bibliography
  • Jennet Conant, Tuxedo Park: A Wall Street Tycoon and the Secret Palace of Science That Changed the Course of World War II (New York: Simon & Schuster, 2002, ISBN 0-684-87287-0) pp. 231–232.
  • Department of Transportation and Department of Defense (2006–02). "2005 Federal Radionavigation Plan" (PDF). Retrieved 26 February 2006. 

External links[edit]