GPS World

Tag: GPS backup

  • eLoran Progresses Toward GPS Back-Up Role in U.S., Europe

    eLoran Progresses Toward GPS Back-Up Role in U.S., Europe

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    (fFrom left) Congressman LoBiondo, UrsaNav CEO Chuck Schue and Harris Division President Pam Drew. (hoto Credit: Andrei Grebnev, UrsaNav)

    As of June 19, eLoran is on the air in the United States. The low-frequency signal emanates from a single station, a former U.S. Coast Guard Loran Unit in Wildwood, N.J., which sports a 625-foot signal mast that has been out of action for five years. The signal is receivable at distances of up to 1,000 miles.

    The facility began generating eLoran pulses at the press of a command button by Congressman Frank LoBiondo (R, N.J). Present for the ceremonial start of a 12-month demonstration and research program under the aegis of the Department of Homeland Security were project participants Charles Schue, CEO of UrsaNav; Pam Drew, president of Harris Information Systems; and Dana Goward, president of the Resilient Navigation and Timing Foundation.

    Brief remarks delivered at the turn-on collectively made the key points that:

    • GPS services are essential to national and economic security, yet are vulnerable to disruption.
    • The eLoran navigation and communications signal has  features that are complementary to GPS, making it difficult to disrupt; further, it could be an important part of enabling UAVs to fly safely in our airspace.
    • The U.S. Federal Radionavigation Plan cites not being critically dependent upon a single system for positioning, navigation, and timing as a national policy objective. The plan specifically identifies eLoran testing as an important step toward reaching that objective.

    The two engineering companies, UrsaNav, a supplier of eLoran technology, equipment, and services, and Harris (which recently acquired Exelis), provide funding and technology for the tests supported by the U.S. Coast Guard, Department of Defense, Department of Homeland Security and other federal agencies under a Cooperative Research and Development Agreement (CRADA) announced in May.

    The team will evaluate eLoran as a potential complementary system to GPS, exploring the capabilities and use methods of eLoran in depth to identify all strengths, capacities, and potential vulnerabilities of the technology. One goal of the CRADA is to reduce the size, weight, cost, power needs and other aspects of Loran, similar to what has evolved with GPS.

    “This is a phoenix arriving. We have the opportunity to add 2015 technology to the older idea,” said Schue of UrsaNav, once Coast Guard commanding officer at the former Loran station. “A prudent mariner always has two systems to navigate.”

    Dana Goward, also a retired Coast Guardsman whose non-profit Resilient Navigation and Timing Foundation is working on the project, stated that eLoran can attain positioning accuracy of six meters or better.

    “We will explore many places eLoran can be deployed where GPS isn’t available such as deep canyons, through buildings, in foliage and under water,” added Harris Corp.’s Drew. “We’re involved with unmanned aerial drones, and eLoran could be key. There are applications for civilian and military uses.”

    In this GPS World exclusive video, Admiral Thad Allen, former commandant of the U.S. Coast Guard, discusses PNT alternatives to GPS for navigation, including eLoran and the activation this week of the signal on the eLoran tower in New Jersey.

    eLoran in Europe

    Matters have moved a little further along in Europe. In 2013, the General Lighthouse Authorities of the UK & Ireland (GLA) established prototype eLoran Initial Operating Capability (IOC) in the United Kingdom, where eLoran now delivers PNT data at the 10-meter level from a network of high-power, low frequency, terrestrial transmitters.

    “To get high accuracy from eLoran requires accurate calibration of Additional Secondary Factor (ASF) through measurement,” according to paper delivered at the Institute of Navigation’s 2015 Pacific PNT meeting. “Can eLoran Deliver Resilient PNT?” was authored by Nick Ward, Chris Hargreaves, Paul Williams, and Martin Bransby of the GLA.

    The older Loran-C system suffered from significant positioning bias errors due to a number of radio frequency signal propagation delay factors, they write. “The Primary Factor (PF) is due to the signal travelling slower in air than free-space, the Secondary Factor (SF) is due to the presence of the Earth’s surface and the electrical properties of the oceans. Additional Secondary Factor (ASF) is due to the additional electrical resistance encountered by non-seawater terrain, land, mountains, deserts, and so on. PF and SF can be modeled, but to get high accuracy from eLoran requires accurate calibration of ASF through measurement.

    “To do this,” they continue, “ASF surveying and mapping has been conducted along the port approach channels at Aberdeen; along the Firth of Forth; Middlesbrough; Hull and the Humber Estuary Traffic Separation Scheme (TSS); Harwich and Felixstowe; The ports of London, Medway and the approaches past the London Array wind-farm and also through the Dover Straits.

    “To complement these services, seven differential-Loran (DLoran) Reference-Stations, one located close to each of these survey areas have been established. These stations monitor the time of arrival of the received eLoran signals, and generate differential-corrections that are broadcast via the Anthorn Loran Data Channel (LDC), to account for temporal variations in these ASF maps.

    “Making use of these ASF maps, combined with the locally-produced differential corrections, can allow a maritime user of eLoran IOC to obtain position accuracy of the order of 10m (95%), within a radius of 30 to 50 km of the DLoran reference station.”

    See also “Back-up to Vulnerable GPS Signals Required for Busy Shipping Lanes.”

    The GLA authors conclude that:

    1. eLoran can deliver Resilient PNT and this has been demonstrated on several vessels.
    2. Seamless handover from primary (GPS) to secondary (eLoran) positioning source has been successfully implemented.
    3. Surveying and mapping of ASF has been carried out for several major ports and the required levels of performance demonstrated.
    4. DLoran reference stations to correct for short-term, temporal variations have been installed and commissioned.
    5. Good levels of performance have also been demonstrated for coastal voyage phase away from the ASF surveyed areas.

    eDLoran in Rotterdam. The July 2014 issue of GPS World presented a cover story showing results of a newer version, enhanced differential Loran (eDLoran), yielding position accuracies of approximately 5 meters.

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    eDLoran: The Next-Gen Loran

    Potential GNSS Back-up Improves to GPS-Level Accuracy

    A new enhanced differential Loran system demonstrates 5-meter accuracy not achievable by the current DLoran system, and requires less expensive reference stations. A prototype tested in Rotterdam’s Europort area uses standard mobile telecom networks and the Internet to reduce correction data latency — a key source of error — by one to two orders of magnitude.

    By Durk van Willigen, René Kellenbach, Cees Dekker, and Wim van Buuren

    Figure 12. The large ship symbol (grey) is derived from the GPS-RTK receiver of the Rotterdam pilots. The width of the ship symbol is 10 meters and the speed-over-ground was 11 kts. The red triangle is generated by the eDLoran receiver and remains between the required ± 5 meter limits for eDLoran.
    Figure 12. The large ship symbol (grey) is derived from the GPS-RTK receiver of the Rotterdam pilots. The width of the ship symbol is 10 meters and the speed-over-ground was 11 kts. The red triangle is generated by the eDLoran receiver and remains between the required ± 5 meter limits for eDLoran.
    Figure 13. The red track is based on raw eLoran data without any corrections. The transparent blue line is made by GPS-RTK and is widened to 10 meters giving the required ± 5 meter limits of eDLoran. The white line is output from the eDLoran receiver which stays within the borders of the 10 meter wide transparent blue line.
    Figure 13. The red track is based on raw eLoran data without any corrections. The transparent blue line is made by GPS-RTK and is widened to 10 meters giving the required ± 5 meter limits of eDLoran. The white line is output from the eDLoran receiver which stays within the borders of the 10 meter wide transparent blue line.

    The GLA authors from the UK give a perspective on the Rotterdam project, as follows:

    “A compatible system (eDLoran) has been developed for operation by ships’ pilots on the Europort approach to the Port of Rotterdam.

    “However, Loran is a regional system dependent on international collaboration. The 9 transmitters in northern Europe are operated by Denmark, France, Germany, Norway and the UK.

    “Both Norway and France have declared an intention to cease Loran transmissions at the end of 2015. Moreover, France intends to dismantle its Loran infrastructure in 2016. Arrangements for the commercial operation of the infrastructure are being investigated, but this depends on some form of regional agreement. The European Union appears to have no policy for resilient PNT, the European Radio Navigation Plan having twice been drafted but never published. The view seems to bee that the introduction of Galileo will achieve resilient PNT, which it will not.”

    And Elsewhere

    South Korea is implementing a national eLoran service, and it is understood that similar plans are being considered in Russia and China.

    Meanwhile, the U.S. Army is interested in eLoran PNT for the warfighter.

  • Bill Supports eLoran as GPS Backup

    A bi-partisan group of legislators led by Congressman John Garamendi (D-Calif.) has introduced a bill that would require the U.S. Secretary of Defense to establish a backup for GPS within three years using eLoran.

    The National Positioning, Navigation, and Timing Resilience and Security Act of 2015, H.R. 1678, was co-sponsored by Congressmen Duncan Hunter (R-Calif.), Peter DeFazio (D-Ore.), and Frank LoBiondo (R-N.J). Garamendi is the ranking member of the House Transportation and uInfrastructure Subcommittee on the Coast Guard and Maritime Transportation.

    H.R. 1678 would require the secretary of defense, in coordination with the commandant of the Coast Guard and the secretary of transportation, to establish and sustain a reliable, land-based positioning and navigation system that will complement and backup America’s GPS for military and civilian uses by using eLoran.

    eLoran is the government’s existing and underused long-range navigation system infrastructure. The backup system would step in when GPS signals are corrupted, degraded, unreliable, or otherwise unavailable. A terrestrial-based system, eLoran wouldn’t be affected by atmospheric interruptions such as solar storms, or jamming or spoofing aimed at GPS.

    The bill directs the secretary of defense to incorporate the expertise and contributions of the private sector to quickly establish  system architecture, as well as build and operate the system.

    “GPS is much more than a LCD screen on your dashboard. It’s a technology used for much of our nation’s critical infrastructure and by almost every major industry in America, as well as the military, law enforcement, and first responders,” Garamendi said in a press release. “We are increasingly reliant on the precision, navigation, and timing services that GPS provides. From land navigation on cell phones to a timing source for our national infrastructure, we need a reliable backup system to GPS.”

    Garamendi said the bill would make the nation’s geopositioning infrastructure more resilient to “threats both natural and nefarious.” “A backup system could also reach places that GPS currently cannot, such as inside many buildings. This would help first responders and law enforcement more effectively protect the public,” he added.

    Other members of Congress are expected to sign on as co-sponsors after Congress returns from its spring recess, according to Dana A. Goward, president and executive director, Resilient Navigation and Timing Foundation.

    The eLoran PNT system would use enhanced long-range signals (eLoran) from 19 towers around the country, each with approximately a 1,000-mile range providing overlapping fields from which a device can derive its location. The back-up system would use the remaining Loran infrastructure and provide a secure and reliable cybersecurity insurance policy, said the press release.

    The U.S. atomic clock, accurate to one second in 300 million years, also serves as the base timing source for this backup GPS capability. This exceeds the timing needs of modern cell phones, creating an infrastructure backbone that is prepared to handle the evolution of consumer and industry electronic communications in the years ahead, the press release said.

    The bill sets out numerous requirements for the system, saying that it shall:

    • Be wireless, terrestrial, and wide area
    • Provide a precise, high-power 100 kilohertz signal
    • Be resilient and extremely difficult to disrupt or degrade
    • Be able to penetrate underground and inside buildings
    • Take full advantage of existing, unused Loran infrastructure
    • Work in concert with and complement any other similar positioning, navigation and timing systems, including eLoran.

    Since 2004, the federal government has recognized that the absence of a reliable backup system for GPS is a glaring economic and security threat to the United States, and has reaffirmed its interest in developing an eLoran as a reliable, land-based backup for GPS signals, the press release said.

    In January, the United States Army began soliciting information for eLoran receivers for the warfighter, either stand-alone or integrated with GPS, for use in Army and other Department of Defense maritime, aviation, or vehicular platforms, and for position and timing.

    The United Kingdom began using eLoran in October 2014 to protect its shipping lanes, which carry 95 percent of UK trade, in case of GPS signal loss.