Russia’s April 1 GLONASS blackout occurred, ironically, only hours after the U.S. House of Representatives passed legislation to preserve infrastructure that could support a back-up system for GPS that could be used for critical infrastructure and applications in the event of a similar disaster occurring in the United States.
The 2014 Coast Guard Authorization Act requires the Department of Homeland Security (DHS) to halt dismantling and disposal of infrastructure that could be used for a terrestrial system during times and in places where GPS is not available.
DHS had announced in 2008 that it would build such a back-up system, but it never did so, and actually began dismantling, destroying, and divesting itself of Loran equipment and properties. The equipment, facilities, and sites could be used to implement a new-generation eLoran system for GPS back-up, among other applications. Despite strong recommendations to the contrary by its own panel of experts, the Obama administration, DHS, and the Coast Guard moved in 2009 to kill the Loran program.
Ever watchful, Congress has lately become more visibly concerned about the vulnerability of the nation’s space systems. The 2014 National Defense Authorization Act tasked the administration with reporting on how it was going to provide necessary national security capabilities when space systems were disrupted. More recently, Congressmen Duncan Hunter (Republican, California), chair of the House Coast Guard and Marine Transportation Subcommittee, held a hearing at which he expressed his concern that the nation has no back-up for GPS. He also expressed his frustration with the Department of Homeland Security, reporting that “They said they need to do a study about their study.”
Congressman John Garamendi (Democrat, California), commented “GPS will go down one day. The question is, is there a backup?”
The legislation passed by the House authorizes DHS to partner with public or private entities to build a system that would not only backup GPS, but also work indoors, underground and underwater — all characteristics of long-wave Loran technology.
Dana Goward, president of the Resilient Navigation and Timing Foundation, said such a project would be relatively inexpensive. “If the existing equipment and infrastructure are preserved and reused, the system could be restored and put into operation for less than half the cost to dispose of it.”
“It isn’t an issue of money,” Goward continued. “It is a question of the government taking this problem seriously and acting on it.”
The foundation has as offered to partner with the government to build the system.
“Our government has known about this issue for a long time,” Goward said. “At least since 2001. And there has been a standing presidential direction to obtain back-up capability since 2004. But for some reason, it hasn’t yet happened.”
The U.S. government’s official information website about GPS has recently updated its page on eLoran and Loran-C with a tracking log for Coast Guard and Maritime Transportation Act of 2014, which now goes to the Senate.
In the wake of last month’s Expert Advice column on eLoran — “The Low Cost of Protecting America” by Dana Goward of the Resilient Navigation and Timing Foundation — come several positive comments and encouraging developments. Rather than rehearse all the arguments why we should care about this, I’ll repeat the one word that I heard most often in GNSS circles in 2013: jamming. Followed closely by: spoofing.
“I have been advocating strongly for reconsideration of the government’s domestic Loran decision for the last year or so,” writes one reader positioned on Washington’s Beltway, “and specifically working within the Department of Defense (DoD) to ensure it is aware of international developments for eLoran in the UK and South Korea, and the possibilities inherent in other former Loran chains.
“The DoD is beginning to recognize the value of eLoran as a complement to GPS, not only for international missions, but in cooperation with the departments of Transportation and Homeland Security for domestic critical infrastructure.”
Last fall, Don Jewell’s Defense PNT newsletter on the same subject drew this reply from another well-known expert:
“One of the key short-term actions is to prevent the decommissioned [Loran] sites from being sold off for subdivisions. These sites are a national treasure with unique properties: soil conductivity, water content, metal content, and more that are hugely important in siting low-frequency positioning systems. Those long-gone engineers of the 1940s and ’50s knew this and chose accordingly.”
Before last month’s issue appeared but after it had gone to press, President Obama signed the National Defense Authorization Act (NDAA) for 2014. It contained several favorable New Year’s auguries for positioners, navigators, and timers.The act evinced an acute awareness of the vulnerability of space systems to disruption. The act is also a law governing the land. Through it Congress requires the administration to, among other things, explain biennially in its “Space Protection Strategy” report exactly how, in the event space systems are disrupted, DOD and the intelligence community “plan to provide necessary national security capabilities through alternative space, airborne, or ground systems.”
Since said administration acted early in its first term to decommission Loran-C, the congressional directive is pointed.
The next big thing coming up on the GNSS international horizon takes place in Rotterdam, the Netherlands, April 15–17: the European Navigation Conference, ENC-GNSS 2014. It includes a track session on “eLoran and other Low-Frequency Systems,” and I’ll be there with pencil sharpened.
Brad Parkinson will give the ENC keynote, and he is on record as one of an august group of Institute for Defense Analyses experts who unanimously recommended that the existing Loran-C be greatly updated and modernized to eLoran. We should hear more from him on this subject amid the wharves, waterways, and docks of Europe’s largest port (world’s third busiest).
There’s barely room left to report the successful tests of Enhanced Differential Loran (eDLoran) by Dutch specialists Reelektronika: absolute accuracy of 5 meters in the North Sea and in the Rotterdam Europort harbor area.
Highly precise and free for use by anyone with an inexpensive receiver, GPS and other GNSS are great. Their navigation and timing signals have been incorporated into nearly every aspect of modern life, from synchronizing power grids to financial systems, the Internet, telecommunications, and transportation. The U.S. Department of Homeland Security estimates that these signals are used by all 16 of U.S. critical national infrastructure sectors, and are essential to the functioning of 11.
Jamming Threat Growing. When these faint signals can’t be received, people start to feel the impact immediately. Usually outages have minimal impact because they are localized and short-lived. Often they occur because the user is temporarily in an area without a good view of the sky. More and more often, though, they are due to the presence of one of a growing number of people with jamming devices (many of which also block cell phone frequencies).
Inexpensive, easy to obtain, and illegal, jammers are spreading as people become more concerned about privacy and being tracked by their employer, spouse, the National Security Agency, and others. Although the government tries to collect information on jamming incidents, no widespread detection system has been established, and few verbal reports are received. For the calls that do come in, it is often impossible to determine which are because of user error and which are purposeful interference.
For those cases where jamming is discovered, locating and identifying the perpetrator is difficult and often impossible. As one example, in spite of near-daily disruption of GPS that caused the shutdown of a new landing system at Newark International Airport, it took the Federal Aviation Administration and the Federal Communications Commission more than two years of concerted effort to identify the single perpetrator.
If a navigation satellite outage became widespread and lasted more than a few hours because of a major solar flare, software problem, hacker or cyber-attack, most authorities agree that the impacts would be catastrophic. While much of the information is classified, we do know that transportation would immediately become much less efficient and more dangerous; even many traffic lights are coordinated using satellite timing. Telecommunications, financial, energy and other systems would soon begin to fail as their back-up timing systems lost synchronization with each other. Power grids would lose synchronizations and outages may occur as transmission points became overloaded.
More than speculation, these problems have been documented in academic papers, proven in government tests in the United States and the United Kingdom, and the early stages of such impacts have been observed in localized and short-term outages in the United States. Most dramatically, they have been demonstrated by North Korea’s intentional jamming of South Korea.
Spoofing. Of equal concern is the problem of spoofing. The world’s preeminent ethical spoofer of satellite navigation receivers, Todd Humphreys of the University of Texas, Austin, has demonstrated how easy it is to take control of unmanned aircraft and ships on autopilot by sending a slightly stronger navigation signal, making the receiver think it is somewhere other than where it is. Iran claims to have done something similar, capturing a U.S. military drone in 2010. Humphreys has also shown (on paper) how time-stamps on automated financial transactions could be altered through spoofing. This could do things like reverse the buy-sell equation at a stock exchange, allowing someone to sell at a higher price before buying at a lower one.
The Government Solution
What is to be done? The challenges have been extensively documented and discussed since at least the 1990s. In 2004, President Bush issued the National Space Policy (NSPD-39) that addressed the problem. Although portions of it are still classified, contained within the publically releasable section was direction for the U.S. Department of Transportation (DOT) to, in coordination with the Department Homeland Security (DHS): “develop, acquire, operate, and maintain backup position, navigation, and timing capabilities that can support critical transportation, homeland security, and other critical civil and commercial infrastructure applications within the United States, in the event of a disruption of … space-based positioning, navigation, and timing services.”
eLoran Recommended. In response, the two departments consulted numerous experts and commissioned a study by the Institute for Defense Analysis (IDA) to determine what system or systems should be procured. The IDA study team, which included Brad Parkinson, widely recognized as the father of GPS, unanimously recommended that an existing and outdated nation-wide navigation system called Loran-C be greatly updated and modernized to eLoran. Such a system would provide a navigation and timing signal comparable with and complementary to GPS. They concluded that:
“eLoran is the only cost-effective backup for national needs; it is completely interoperable with and independent of GPS, with different propagation and failure mechanisms, plus significantly superior robustness to radio frequency interference and jamming. It is a seamless backup, and its use will deter threats to US national and economic security by disrupting (jamming) GPS reception.”
What the IDA did not find, but that has since become evident, is that establishing an eLoran system could be an important part of a network to identify and locate jamming attempts. Since all eLoran transmitters would be synchronized with GPS, and many navigation receivers would have both GPS and eLoran sensors, differences between the two systems could be immediately detected and reported.
The body in charge of coordinating navigation and timing issues for the federal government is the National Space-Based Position Navigation and Timing Executive Committee (NPEC). It is chaired by the Deputy Secretaries of Transportation and Defense. Responding to early briefings on the IDA report (which was not formally published until 2009), the Departments of Transportation and Homeland Security in 2007 told the NPEC that they had decided eLoran was the right answer. After further federal deliberations over how to create an eLoran system, 2008 saw:
A press release by DHS saying that the department would implement eLoran, using the old Loran-C infrastructure (February 7, 2008)
The DHS 2009 Budget in Brief (February 2008) propose transferring legacy Loran-C systems and $34.5 million/year from Coast Guard to the National Protection & Programs Directorate (NPPD) within DHS, stating:
“The FY 2009 budget transfers the budget authority for the LORAN C system from the United Sates Coast Guard to the NPPD. The Department, acting as Executive Agent, will begin development of enhanced eLORAN as a backup for GPS in the homeland.”
The National PNT Executive Committee endorse the above decisions (March 2008).
Failure to Launch
Unfortunately, DHS funding for 2009 came as part of a continuing resolution, and the Congress did not see fit to approve the transfer of funds from Coast Guard to NPPD.
This was because influential members of Congress wanted the nation to have eLoran, but were concerned about the lack of a plan for transition of this important capability from one agency to another. The administration was asked to develop and submit a plan with with the next budget cycle. A year later, though, no plan had been presented, and the President’s request (and enacted legislation) for 2010 contained no request to move and upgrade the system. In fact, it contained provisions for shutting down and defunding the old Loran-C system without providing funds for NPPD or any other agency to establish the new eLoran capability.
No Solution at All. What happened between one budget year and the next to take the nation from “solution-in-hand” to “no solution at all” is not a matter of public record. Internal administration budget deliberations are not generally released to the public. It does appear, though, that a new administration putting together its first real budget quite rightly wanted to shut down an antiquated system, but did not understand the importance of a new one. This, and many other factors, unquestionably played a role.
Movement Backward
Without any funding, DHS has since conducted several studies and experiments, but has done very little of substance to address this critical infrastructure issue. While Department of Defense (DOD) officials talk about the need for resilience, experts throughout government and industry decry the lack of action, and the Department of Transportation still has acquiring “backup position, navigation, and timing capabilities” on its to-do list, none have seen fit to move forward on their own.
Felling Towers. Worse, DHS is actually reducing the nation’s ability to create eLoran and a wide-area interference detection and mitigation system. An ongoing effort to fell towers and dispose of equipment from the legacy Loran-C system will significantly increase the cost and time-to-operation of the new system the nation needs.
The Way Forward
Fortunately, awareness and understanding of the problem within government, and the general public has continued to grow.
The U.S. National Space-Based Positioning, Navigation, and Timing (PNT) Advisory Board published a seminal white paper in 2010 on the topic, strongly recommending the establishment of an eLoran system. Todd Humphreys, the UK navigation authority, and others have provided numerous graphic demonstrations of the folly of relying upon just one electronic navigation system, and how things can go horribly wrong. Some of these have been well publicized. Other incidents are known only to a few.
There are also signs that the U.S. intelligence, cyber, and defense communities are becoming more and more concerned. North Korea’s repeated jamming of satellite navigation and timing signals has delivered a particularly powerful lesson. South Korea has reacted by committing to establishment of a robust eLoran system. The UK has established an eLoran system and is expanding it. Russia and China have retained their versions of Loran-C and are using it to augment satellite services. Russia has announced it will upgrade its system to eLoran in cooperation with the UK, and China may not be far behind. Saudi Arabia is upgrading its system to eLoran, and India has plans for an eLoran network in the near future. In December, Iran announced it has established a land-based system with “powerful transmitters” that is “completely different with GPS.”
Allies, adversaries, and economic competitors are augmenting satellite services with strong terrestrial ones. The United States will soon be one of only a small number of major economies that does not have a strong, difficult-to-disrupt terrestrial system protecting its critical infrastructure and providing value-added utilities. DOD’s chief information officer expressed interest in eLoran as part of DOD’s pivot to the Pacific. But providing a system at home is not in Defense’s job description, nor should it be.
Respected leaders at the Departments of Transportation and Homeland Security still see this as an important issue that needs to be addressed. The question for them now is not one of technology. The technology decision made in 2008 has since been revalidated by a plethora of academic papers, risk estimates, and white papers. eLoran still appears to be the most effective and least expensive solution available. DOT and DHS must resolve questions of governance and how to fund the system in one of the most difficult federal budgetary climates in decades.
How? The answer could lie in a public-private partnership (P3). In such an arrangement, the government would bring its interests and the infrastructure it owns to the table. An entity in the non-profit sector or industry would provide investment to refurbish the infrastructure, stand up, and operate the system. Such a P3 enterprise could not only pay for itself, but be an on-going source of revenue for both the government and the private entity.
The Business Model: Demand
A well-configured eLoran system can provide navigation accuracy to within 8 to 10 meters and timing accuracy to within 30 nanoseconds. This meets the needs of an estimated 95 percent of users in the United States. While eLoran does not offer the sub-meter precision of a high end, augmented GPS/GNSS system, it has its own advantages. In addition to being very difficult to disrupt, its high-power (typically 400 kW transmitters), low-frequency (100 kHz) signal easily penetrates and is usable underground, inside buildings, and underwater — where satellite and cell phone signals on much higher frequencies cannot reach.
The UK experience with eLoran and private surveys in the United States have shown high commercial demand for a ubiquitous, wireless, precise, and resilient time and navigation service. Power companies want to synchronize grids with a signal that can’t be disrupted by a delivery driver trying to avoid being tracked by his boss. Cell phone companies would be happy to have alternative timing capability in their networks, provided through inexpensive eLoran receivers. Operators of autonomous vehicles want a robust navigation signal and guaranteed communications. And it would be welcomed by the many users who, research shows, rely upon GPS/GNSS time for mission-critical applications, and who have no secondary source on which to fall back in the event of a disruption.
Since eLoran easily penetrates inside buildings, underground, and underwater, it can be used for timing and navigation in many places where no other navigation and timing sources are available. For example, it has been used for underground and underwater navigation. When paired with an accurate satellite signal before going underground or submerging, eLoran could enable a navigation receiver to maintain a comparable level of precision for several hours. Even after that, it would provide the navigator an accurate underground/underwater compass, and a good position.
The eLoran navigation and timing system now in operation in the United Kingdom also generates revenue by transmitting data. While the full potential of this third-party data-channel capability is still being explored, the ability to assure data delivery to, and communicate with such areas is appealing to many commercial and government organizations. Potential first-responders and commercial benefits appear almost limitless.
The Business Model: Costs
The cost for the P3 to standup and operate an eLoran system in the United States would be exceptionally low. Most of the needed infrastructure is already owned by the federal government in the form of the sites for the shuttered Loran-C system. Many of these still have transmission towers and other equipment that could be repurposed. Re-using this infrastructure and equipment would greatly reduce both the time and expense needed, compared to standing up the new system from scratch.
Operating and maintenance costs would also be low. Solid-state equipment, remote monitoring, and other advances in technology make the process of re-establishing a transmission site fairly inexpensive. Today’s eLoran transmitting site consists of a tower, an equipment enclosure for the transmitter, a fence, and a backup generator. With only a modest investment to refurbish existing infrastructure, regular outlays to service capital debt would be minimal, at best.
Some estimates predict that a terrestrial precise navigation and timing system, such as the one established in the United Kingdom and the one up for contract by South Korea, could be established in the continental United States within three years and for approximately $40 million, if the existing infrastructure were repurposed. Operating costs are estimated at approximately $16 million per year.
Business Model: Revenues
Significant national and homeland security concerns, high demand, and low cost (especially compared to any government space program) — clearly, but for a series of unfortunate bureaucratic reasons, eLoran would have been established in the United States, probably as a government-owned and operated system, long ago.
But high demand and low cost are also excellent ingredients for a business enterprise, provided there are sources of revenue. An eLoran P3 could have multiple sources of revenue. Depending upon the type of partnership and business model(s) the government selected, surplus revenue could also be generated to help fund other programs or offset the deficit. Some of the possibilities include:
◾ Guaranteed Delivery Data Transmission. As mentioned earlier, eLoran’s high power and low frequency mean that the signal penetrates where few others will. In addition to navigation and timing information, which are inherent in the basic signal, low-rate data can also be included between the primary pulses. The highest demonstrated data transfer rate to date has been 1300 bps, which is fine for texting and issuing commands. Many believe that, with a modicum of research, that rate can be much higher. As the owner of the high-power transmitter network, the P3 would generate revenue the same as any telecommunications provider: by charging per message or for time on the network.
Applications could include:
• Assured wireless control of remote equipment and vehicles, including indoors, underground and underwater;
• Information delivery to first responders and other crews regardless of location — especially good for pre-programmed emergency and operational commands to evacuate, use another procedure, and so on.
• Immediate device updates and reprogramming. The ability to reach all of the enabled devices on a given network at the speed of light and virtually simultaneously has unlimited potential.
◾ PNT Interference Detection and Monitoring. One of the biggest challenges to countering jamming satellite navigation and timing signals is the lack of a detection network. The eLoran transmitter and receiver network will continuously synchronize with GPS/GNSS signals and instantly detect when differences between the two dissimilar systems occur. Instant reports could be generated to inform federal, state, and local authorities of the anomalies and their locations. Mobile disruptors could even be tracked as they drove down the highway, sailed through the port, or flew across the sky. The P3 could generate revenue by contracting to provide such information to private parties and government agencies concerned about interference incidents.
◾ Licensing Receivers. One of the simplest ways to generate revenue and endow the P3 would be for the government to assess a small fee on every eLoran and satellite navigation receiver sold in the United States. A one dollar fee per unit could generate more than $20 million per year and fund operation of the entire system. Such a fee could be discontinued as other sources of revenue from the system made it unnecessary.
◾ Broad-based User Fees. Since navigation and timing signals are essential to so much U.S. critical infrastructure, a case could be made that the cost to endow the P3 should be spread as broadly as possible across the technologies it supports. For example, a temporary 8-cent fee on every monthly U.S. cell phone and electric bill for just one year could provide enough funding to endow the P3 in perpetuity.
◾ Value-Added Services For High-End Users. More than 90 percent of the users of precise time in the United States require it at the microsecond (1,000 nanoseconds) level of accuracy. eLoran can provide a signal accurate to 30 nanoseconds. To achieve that level of precision, the eLoran network transmits data that compensates for low-frequency signal propagation over non-homogenous terrain. This correction data could be encrypted. Most users would access the signal at the microsecond level of accuracy for free. Revenue could be generated by charging those who desire the higher level of precision a fee for the encrypted portion of the signal.
eLoran is an essential national and homeland security capability. The above list of potential revenue sources is just a sampling of the many ways a P3 could be funded. The point is that financing the enterprise need not come from tax dollars, and should not be an obstacle to its creation.
The Public-Private-Partnership
The U.S. government has had some great successes solving previously intractable problems through public-private-partnerships. Probably the best known of these are the P3s formed for housing on military bases. Establishing a business model that has private partners constructing and managing on-base housing produced more and higher quality housing for our troops.
Such arragnements must be carefully managed, however. Both the Congressional Budge Office and the Office of Management and Budget are understandably concerned that P3s may get a project going, but soon the costs may fall entirely on the government.
Success in any endeavor often depends upon its execution. The type of partnership the government selects and creates will be key. While, at its heart, a P3 is just a contract, the nature and provisions of government contracts are endlessly varied. Issues to address will include how the infrastructure is provided, if it is to be retained in perpetuity by the government or will be conveyed to the private party, what length of contract will allow the private partner to recoup its initial investment, and the business model(s) to be pursued.
The type of governance will also be important. Models vary from establishment of a self-funded government corporation to oversee daily operations, to an agency-supervised, performance-based contract that only requires regular reports on system availability and performance.
Of course, the concerns of CBO and OMB must be met. Fortunately, the federal government is not without experience with P3s. Also, there are many supporting resources available, such as the National Council for Public Private Partnerships.
We Have to Do It
Establishing a public-private partnership will bring together the best of both the government and the private sector. For its part, the government will bring the legacy infrastructure and its interest in safeguarding the public good to the table. The private sector will bring financing, technical know-how and innovation. A better system for America will result than would have been possible if either were to act alone.
It is unquestionably in our urgent national interest to address the problem now, before jamming becomes more widespread, or we have a larger, more damaging event. The need is clear. The technology exists and works great. All that remains is for dedicated leaders within government and the private sector to work together and implement the solution.
Dana A. Goward is the president and executive Director of the Resilient Navigation and Timing Foundation, a non-profit organization devoted to educating people about the need for and encouraging resilient navigation and timing ecosystems with services that complement each other and have different failure modes. See www.RNTFnd.org.
UrsaNav’s President, Charles Schue, shown accepting the transmitter from Nautel’s President, Peter Conlon.
After extensive Final Acceptance Testing at Nautel’s Hackett’s Cove, NS facility, UrsaNav has accepted delivery of the first production NL40 Loran-C and Enhanced Loran (eLoran) transmitter. This seventh-generation Loran transmitter technology is the culmination of more than six years of collaborative development between the two companies.
The transmitter successfully met or exceeded all of the requirements of the U.S. Coast Guard “Specification of the Transmitted Loran-C Signal.” Testing was conducted into a simulated antenna matching the characteristics of a U.S. Coast Guard “standard” 625-foot top-loaded monopole. The NL-Series transmitters are capable of transmitting Loran-C, eLoran, Chayka, and eChayka in any combination at power levels exceeding one megawatt. They are qualified for today, and prepared for tomorrow, UrsaNav said.
“Resilient PNT begins with complementary technologies, layered one upon the other in such a way that the user is ensured improved continuity of operations over a sole-source solution,” said UrsaNav President Charles Schue. “eLoran is the terrestrial co-primary complement to GNSS, and our technology makes eLoran the most economical, efficient, and wide-area alternative when GNSS is not available.”
A couple of years ago, wearing a different hat, I found myself on a guided tour of a key military C2 (Command and Control center) that was about as big as a football field and was to be deployed somewhere in Southwest Asia. My colleagues and I, who are all GPS SMEs (Global Positioning System Subject Matter Experts), asked the same question of almost everyone we saw that day. Near the end of the day and the tour, we had yet to receive an adequate answer. The typical response was, “Please save that question for our senior communications officer.”
Finally, at the end of the tour and demonstration, we met the communications chief, and we once again asked our persistent and, for some of us paramount, question: “What would happen if we walked into this facility in the middle of a major military operation and activated a Coke-can-size GPS jammer that we were surreptitiously carrying in a backpack? In other words, what would happen if we disrupted your GPS signal reception?”
The communications expert thought awhile and then answered. Unfortunately, the answer was a bit perplexing and yet all too common, inside the military and out. The communications officer hesitantly replied, “Well, this is a C2 center, and we are all about computers, networks and communications, and although I have to admit I don’t know much about GPS, other than we use it to navigate our military and civilian vehicles, I guess I would have to say it would not make any difference. In fact I am not even sure we would notice.”
Quick as lightning, before I even had a chance to challenge the response or thought process, a grizzled old E9, who proved his operational savvy that day, interjected, “Beg your pardon, but all of our radios, computers, networks and communications gear are referenced and synchronized to GPS time. A GPS jammer would take us out of business until we brought up our backup atomic reference system. So, initially a Coke-can jammer activated in our facility would be catastrophic, but we would soon be back in business because we have backup atomic reference systems.”
Fast-forward, and today that transition between GPS and atomic reference system is seamless. There is no down time, and yet the systems still run on GPS time. But during that initial visit, I could tell by the looks on the junior communications officers faces that surrounded us that, while they appreciated the save by the old chief, they were also still wondering, just how pervasive is the actual impact of GPS time for computers, networks and communications?
The answer is simple. The world as we know it today runs on GPS time.
GPS — Time and Frequency
This is unfortunately a scenario my colleagues and I encounter all too often. While it is not my intention to launch into GPS 101, it bears repeating that of the approximately 3.5-billion-plus users of GPS and PNT (Position, Navigation and Timing) systems in the world today, 90% use the signals for incredibly accurate time-keeping and frequency stability, not just for positioning and navigation.
Indeed, GPS SVs (space or satellite vehicles) today typically contain either three or four atomic reference systems (atomic clocks), primarily long-term, stable Rubidium systems with shorter term stable Cesium clocks as a Primary Reference Source, that continually broadcast Stratum-1 timing signals with stability on the order of 1×10-E13 or a pico second (a trillionth of a second) or greater.
For the mathematically challenged, that means the stability of the atomic clocks are such that if the GPS atomic reference system could be maintained in a perfect environment for the lifetime of the clock, nominally 20-30 years for Rubidium systems, it would never lose a second of time. To put this number in perspective, consider that the navigation revolution (easily the biggest change in navigation since the sextant was invented) brought about by Harrison’s chronometer, perfected in 1759, allowed accurate navigation by Longitude and Latitude, by keeping and transferring time aboard ships with accuracies in the 10-second range over periods of weeks. And even though at the time it was hailed as a chronometer, its lack of accuracy is such that most navigators today could not tolerate the inaccurate time or lack of stability, not when they can measure time to the trillionth of a second or better simply by receiving a free GPS timing and frequency signal available globally.
Interestingly, the clocks on the Boeing IIF GPS satellites (currently four SVs on orbit), which certainly have other issues, are proving to be the most stable Rubidium atomic reference systems ever flown in space to date, as they are currently displaying an unexpectedly high degree of frequency stability. Hopes are that future spaceborne atomic reference systems (such as in the GPS III LMCO SVs) may achieve two orders of magnitude greater stability at 1×10-E15. Compared to Harrison’s chronometer, that is an improvement on the order of 17 orders of magnitude!
Now, if you are still wondering what all this clock stability means to you, consider that one nanosecond, or merely one billionth of a second, equates to a foot of positioning accuracy on the Earth, but even more importantly, for 90% of GPS users globally, time and frequency stability equates to an incredible, dependable, stable, ubiquitous timing source for the initiation and synchronization of networks and communications systems worldwide.
When you consider that almost everything we do today involves timing, networks, computers and communications in some form, it also means that when we consider our (United States) Critical National Infrastructure (there are 16 critical infrastructure sectors defined today), all 16 depend in some form or function on GPS time and frequency stability. That is a sobering thought, and is exactly why we often use the words “ubiquitous” and “utility” when referring to the Global Positioning System. Make no mistake about it: almost every major country you can name today has the same dependency on time and frequency stability for their Critical National Infrastructures, and the majority use GPS as their primary timing, frequency and/or reference source.
Dependence
Some of you — and you don’t necessarily have to be a conspiracy theorist to think this way — will immediately see this dependence on one space constellation or system as a vulnerability. You would be correct, if there were no backup systems, augmentations or alternatives. Fortunately, just like the military C2 center, the majority of our Critical National Infrastructure sectors today have interim or temporary backups. While you should view that as a fortunate circumstance, it is also the limiting factor, or LIMFAC, in our infrastructure; the majority of the backups are terrestrial, oftentimes temporary in nature, and they rarely have the same degree of coverage, reliability or stability of GPS.
Many of you may still be saying to yourself, so what? Here’s the so what: without GPS timing and frequency stability, we as a nation may be able to generate electricity, but we would not be able to distribute it. We may be able to drill for oil and produce products such as gasoline and diesel, but we could not distribute them, and you would not be able to dispense or purchase them at the pump. You could earn money, but you would not be able to access your bank account or bank records online or at an ATM. All of these systems depend on computers, networks and communications, and they all depend on GPS time and frequency for synchronization. Get the point!?
Knee-Jerk Reactions
Unfortunately, this realization has led many of our senior leaders in the services and the federal government, who should know better, to make broad and blanket knee-jerk statements concerning the need to replace GPS that are entirely unwarranted. As I said earlier, if you think of GPS as a global utility, that is exactly what it is. Then you must treat it just like you would electricity, for example. Certainly much of the world runs on electricity, and as you have seen, much of the world also runs on or certainly depends on GPS timing and frequency signals.
However, as much as we depend on electricity, we don’t scream “find another energy source” every time the lights go out due to a storm, or power cables are cut by an accident or a farmer’s plow. Instead, prudence dictates that we plan for these occurrences, and we utilize other temporary or alternative methods of generating electricity such as backup generators. Indeed, we routinely use solar power, wind power, and batteries to hold us over until the main power is restored.
We should think of GPS in the same way. When the GPS signal is interrupted, we should not immediately call it unreliable. Rather, we should use atomic clocks, inertial systems, and other PNT systems until the gold standard GPS signals are once again available. The solution is all in how you parse the problem.
eLORAN
If there were only a persistent, wide-area, wireless solution to our problem. Fortunately, there is, and as a nation we are well acquainted with one answer and one solution, which in my opinion is the answer and a time-proven solution. For more than 70 years, since before WWII until 2010, we as a nation had the answer. The near-perfect backup and/or augmentation system for GPS was already in place; it was a coterminous system originally designated LORAN-A (long range navigation). The legacy system (LORAN-C) was in the process (90% complete) of being updated to eLORAN, a modern digital system, when inexplicably the current administration decided the entire project was a waste of money; it’s a well known government condition or disease better known as myopia or shortsightedness. Now that same administration is spending more money every year ($50M) to tear down the LORAN-C and existing e-LORAN infrastructure and remediating land at the 28 transmission sites. The annual cost of operating the e-LORAN system for one year ($16M) means these same funds could operate the eLORAN system for more than three years.
The sad part is that while our government is wasting taxpayer dollars in a severely constrained, sequestered budget environment, destroying badly needed LORAN-C and eLoran infrastructure, the rest of the world is busy building modern eLORAN systems (there are currently ~75 LORAN towers in the world today) as a backup and augmentation to GPS — countries such as Great Britain, Japan, South Korea, and Russia with their CHAYKA system, just to name a few.
A recent RNTF (Resilient Navigation and Timing Foundation) white paper (more on this new organization later) on GPS and LORAN points out that an independent think tank known as IDA (the Institute for Defense Analyses), an organization of which I am proud to be a member and which includes Dr. Bradford Parkinson, who many call the father of GPS, recently conducted a study on GPS and LORAN and recommended that, “an existing and outdated nationwide navigation system called ‘Loran-C’ be greatly updated and modernized to ‘eLoran’.’’ Such a system would provide a navigation and timing signal comparable with and complementary to GPS. The IDA study concluded that: “eLoran is the only cost-effective backup for national needs; it is completely interoperable with and independent of GPS, with different propagation and failure mechanisms, plus significantly superior robustness to radio frequency interference and jamming. It is a seamless backup, and its use will deter threats to U.S. national and economic security by disrupting (jamming) of GPS reception.”
The story of how the United States, which pioneered LORAN, wound up without an eLORAN system today, would be comical if it were not so sad. It is a long and sometimes incredulous tale, as Shakespeare once said, “full of sound and fury,” that I will not take the time to relate; however, I will say that it is not too late. Indeed, if we were to merely admit our mistakes and take the money budgeted for one year of LORAN-C and eLORAN destruction, we could not only build an entirely modern eLORAN system (for ~$40M) but we could operate it for the better part of a year while we figured out ways to make it pay for itself, and believe me when I say there are numerous viable courses of action that make this a real possibility. Then we, as a nation, would not only have a 4,000 KW terrestrial backup and augmentation to GPS, but we would have a backup and augmentation for timing and frequency stability for all of our Critical National Infrastructure sectors that would be nearly impossible to jam or spoof. Consequently, if you can’t jam or spoof the backup, then why bother trying to jam or spoof the primary system, GPS? In this instance, a modern e-LORAN system becomes a security blanket for GPS as well. It is indeed a win/win proposition.
NSPD-39 and RNTF
Lest you think I am a lone voice crying in the wilderness, in 2004 President Bush issued a National Space Policy (NSPD-39) that addressed the problem of GPS dependence. The space policy directed DOT and DHS (Departments of Transportation and Homeland Security) to find a suitable backup and augmentation for GPS. Six years later, a new administration unabashedly began destroying the only viable system that currently meets the parameters spelled out in NSPD-39. Fortunately, there are many today in and out of government that think as I do, and fortuitously they are doing something about it.
Several months ago, I wrote about Charles (Chuck) Schue and his new digital e-LORAN system at UrsaNav being tested and supported by a CRADA or Cooperative Research and Development Agreement with the U.S. Government, and I promise you an update on that endeavor soon.
Now there is an independent non-governmental foundation, the Resilient Navigation and Timing Foundation (RNTF), that supports a P3, or Private-Public-Partnership, to help develop and fund eLORAN as a private/public leased service to the government, and any other interested parties for that matter. In other words, the foundation proposes, among other ideas, to build and operate a modern digital eLORAN system for the United States, for all the reasons mentioned earlier, and lease that service to the U.S. government among others. Using P3 means that in this sequestered budget environment there are no upfront development or deployment costs to the government, and yet the system that augments and backs up GPS and critical timing for our Critical National Infrastructure is in place and operating as a private entity, employing people, paying taxes and providing a critical service. As I said, a winning proposition for all concerned.
If that were not enough, just this week the GAO came out with a report entitled GPS Disruptions: Efforts to Assess Risks to Critical Infrastructure and Coordinate Agency Actions Should Be Enhanced. You can find the highlights for the report at the following link: http://www.gao.gov/products/GAO-14-15. Once there, you can click on the PDF link for the report, which is about 58 pages. So, it is a hot topic, and one that can be easily solved once common sense again reigns in our government.
What Is Don Reading?
This month, I am going to recommend two edited books that are worlds apart in concept but are both highly related to the use of GPS, one theoretically and the other physically and fundamentally.
The Global Positioning System: Theory and Applications, by Parkinson and Spilker.
The Global Positioning System: Theory and Applications,
by Dr. Bradford Parkinson and Dr. James Spilker
1996, American Institute of Aeronautics and Astronautics
ISBN 978-1-56347-106-3
This exhaustive two-volume compendium of GPS knowledge is my daily bible for almost any GPS technical query you can muster. The two volumes total 781 pages and, truth be told, they are certainly doorstops, and while they are essential to your encyclopedic knowledge of GPS, they are certainly not to be carried around as textbooks. They are reference books, and the kind that should remain in your library at home. I treat my copies very gingerly, since they are about to fall apart from constant use. Plus, both volumes are signed by both editors, since they are both close friends and colleagues — but that is not why I recommend them. If Dr. Bradford Parkinson is the father of GPS, then Dr. James Spilker is the father of the GPS frequency and signal structure. Both Brad and Jim are currently Professors Emeritus at Stanford University and we visit on a regular basis, but again, friendship does not enter into my recommending these volumes.
I recommend them because they are simply the best compiled and edited volumes on GPS that exist today. They are authoritative and technical to a fault. As I said before, the word exhaustive comes to mind, and frankly, I don’t know how any GPS aficionado or SME could make it through the day without these incredible reference tools. I know from first-hand knowledge that both Brad and Jim have been approached about an updated edition, but I don’t know how they would find the time. They are both in great demand and are constantly writing and speaking about GPS in venues around the globe. But it would be wonderful if they could fit it in. Now a digital, searchable version — that would be something.
Guide to Super Snipers, Soldier of Fortune Magazine, edited by Brown and Spencer.
Guide to Super Snipers, Soldier of Fortune Magazine,
edited by Lt. Col. Robert K. Brown and Vann Spencer
2013, Skyhorse Publishing
ISBN 978-1-62636-067-9
This book is an edited history of snipers and their equipment that in the last 15 years has included GPS and other PNT systems on a consistent basis. Soldier of Fortune magazine and the editors interviewed literally hundreds of snipers around the world, and this is their story. Some of the snipers made headlines, like Audi Murphy, and were popular American heroes. Others you will have never heard of, but that does not make them any less meaningful or important in the roles they have played keeping their country safe.
This book includes great details about legacy and current sniper rifles and the expert marksmen behind the scopes and sights. It may be more than you ever wanted to know about the art and science of snipers, but it is an inspiring and patriotic book that many will thoroughly enjoy. Be aware there are numerous typographical and grammatical errors — try not to let that impair your enjoyment of this one-of-a-kind book.
Until next time, visit the RNTF site, support eLORAN, read a good book, and I wish you happy navigating.
eLORAN Initial Operational Capability at the Port of Dover
An overview of the work of the General Lighthouse Authorities of the United Kingdom and Ireland on the implementation of Enhanced Loran Initial Operational Capability (IOC) in the waters around Great Britain. eLoran is the latest in the longstanding and proven series of low-frequency, LOng-RAnge Navigation systems. It evolved from Loran-C in response to the 2001 Volpe Report on GPS vulnerability. It vastly improves upon previous Loran systems with updated equipment, signals, and operating procedures.
By Paul Williams and Chris Hargreaves
GPS/GNSS is everywhere! It is used in many ship’s systems (Figure 1), but it is vulnerable to interference both intentional and unintentional.
Its output is displayed on the electronic chart display and information system; is transmitted to other vessels using the Automatic Identification System (AIS); is used to calibrate the gyro compass; is used in the radar; is connected to the digital selective calling, its reported position transmitted at the push of the emergency button for search-and-rescue; is in the vessel data recorder, the dynamic positioning system, surveying equipment, the ship’s entertainment system for aiming the satellite dish; and it even synchronizes the ship’s clocks!
28 days worth of ship-traffic data for the Strait of Dover.
GNSS is also used in marine Aids-to-Navigation (AtoN) provision, for deploying buoys and lights, AIS transponders, and AtoN position monitoring, and its precise timing capabilities are used to synchronise the lights along an approach channel to improve conspicuity.
GNSS (effectively GPS) has become the primary Aid-to-Navigation (AtoN) used by all professional and most other mariners. The vulnerability of GNSS to space weather and interference (unintentional and criminal jamming) means that a backup system is needed to achieve resilient Position, Navigation, and Timing (PNT) for e-Navigation. Though the probability of losing GNSS may be low, the consequential impact could be very high, and maintaining an appropriate balance of physical and radionavigation AtoNs is vital for e-Navigation.
Figure 1. GPS is used in many ship’s systems.
The International Maritime Organisation seeks to develop a strategic vision for e-Navigation, integrating existing and new navigational tools in an all-embracing system, contributing to enhanced navigational safety and environmental protection, while reducing the burden on the navigator. One of IMO’s requirements for e-Navigation is that it should be resilient — robust, reliable and dependable.
The General Lighthouse Authorities of the United Kingdom and Ireland (GLAs) have the statutory responsibility to provide marine AtoNs around the coast of England, Wales, Ireland, and Scotland. It has become clear over recent years that if the GLA chose to implement eLoran, it could rationalize its physical AtoN infrastructure, removing some lights and other physical aids, and on balance actually reduce costs by implementing eLoran. Indeed, compared to other possible resilient PNT options such as GNSS hardening, radar absolute positioning, increasing physical AtoN provision, eLoran would save the GLAs £25.6M over a nominal system lifespan of 10 years from the introduction of e-Navigation services in 2018 to 2028.
Not So Old-Fashioned. How does the new eLoran differ from the old, outdated, Loran-C system? The core signal of eLoran is pretty much the same as Loran-C, but tolerances have been tightened up. Things like carrier zero crossing points, half-cycle peaks, ECDs, transmission timing, signal power, signal availability, power supply resilience have all been upgraded, taking advantage of improvements in technology allowing us to better appease the so-called four horsemen of navigation: accuracy, availability, continuity, and integrity.
SAM control is a thing of the past, and eLoran transmitters are synchronised directly to UTC. This means that their times of transmission can be predicted. Having stations independently synchronised to UTC means that the mariner no longer has to rely on old-fashioned hyperbolic navigation. Charts with hyperbolic lines of position on them are also a thing of the past. A modern eLoran receiver works just like a GPS receiver, employing signals from all available transmitters in its position solution. With GPS those transmitters are moving in space; in eLoran the transmitters are fixed onto the surface of the Earth.
Reelektronika LORADD receiver, only 3 centimeters tall.
Modern receivers are small (photo). They use off-the-shelf, high-performance processors, and the receiver is written in software, allowing a lot of flexibility.
Three transmitters are sufficient to give you position; four or preferably five signals are better for integrity. But for timing and frequency applications you only need one transmitter. The Anthorn station in the UK can cover the entire UK and Ireland with a radio signal that has stability enough to satisfy the Stratum 1 frequency source requirement for steering the clocks of telecom networks, and Anthorn has not even been upgraded to full eLoran standard yet!
One of the big differences between Loran-C and eLoran is that eLoran now has a data channel. Some of the Loran pulses of each pulse group are modulated so that data can be sent over the 100kHz signal. This allows service providers to send integrity alerts, and application-specific data, like UTC time, and differential-Loran (DLoran) and DGPS corrections. In Europe this is implemented by the already internationally standardised Eurofix system.
A parallel can be drawn with GPS signals, which contain a navigation component (pseudorandom noise code and/or carrier phase) and modulated data. Some options for data channel technology are still evolving with 1500 bits per second demonstrated, and 3000 bps possible. That may not sound very much to salt-of-the-earth communications engineers, but for Loran it’s pretty impressive, especially when you consider prototype attempts at Loran data communications in the past have been limited to 30 to 250 bps.
Maritime Applications Services
How do we apply eLoran to something like the maritime application of port approach? It is important to remember that the receiver operates by measuring how long it takes a groundwave radio signal to travel over the surface of the earth. An eLoran receiver assumes that the world is made entirely of seawater, for which it has a very accurate propagation model built in. The receiver does not, and indeed cannot, know about any land along the propagation path; and land slows the signal down, perhaps by as much as a few microseconds, over typical propagation distances.
So the service provider must survey the effects of the land masses in the area of coverage. The Additional Secondary Factors (ASFs) of all the stations across the proposed service area are therefore mapped. The ASF survey is a once-and-for-all task, but it needs to be done and the ASFs published. In the old days, hyperbolic lines would be “grid warped,” or tables would be published on paper for the navigator to enter values manually. But with modern eLoran receivers containing large amounts of memory, quite detailed ASF maps can be stored in the mariner’s receiver.
ASFs depend on the electrical conductivity of the surface over which the eLoran signal travels. The conductivity changes with the constitution and moisture content of the earth. This means that the ASF along a path varies over a period of time —perhaps by as much as a few hundred nanoseconds over a year. Because the ASFs in a receiver are fixed, a method is needed to correct for this temporal ASF variation. In order to monitor this variation, a reference station is installed close to the harbor or point of use of the eLoran service. This DLoran reference station measures the temporal changes in the signals’ arrival times due to changing ASFs, transmitter variations, and weather effects.
The phrase “reference station” conjures up images of expensive buildings, amenities, and hordes of personnel and associated support services. However, a DLoran reference station is a small box sitting in the corner of a room connected to a small eLoran receive antenna on the roof, and to the Internet. It sends differential corrections over the Internet to an eLoran transmitter, which then broadcasts them to the mariner’s receiver over the Loran Data Channel, for example Eurofix.
Note that a DLoran reference station does not transmit a radio signal. It does not need a transmitter itself; it uses the Internet and the eLoran signal to disseminate its real time data. The mariner uses the same eLoran receiver to receive both the navigation signal AND the differential corrections.
So the process is: map ASFs once; run a reference station; and broadcast corrections. That’s it! With good signal-to-noise ratio and transmitter geometry, 10-meter or better accuracy can be obtained.
Measuring ASFs
The GLA have had the ability to measure ASFs for several years, using a combination of commercial hardware and proprietary software (Figure 2).
Figure 2. GLA-produced software for ASF survey, processing, and validation.
The software, written in Matlab, shows a real-time plot of the survey as it progresses. The ASF values are color-coded according to magnitude. The software can also process the ASF data once it has been measured, to get the best performance out of it. The real-time capabilities of the software allow the determination of the quality of the data while aboard the ship, rather than having to wait until back in the laboratory. Statistical analysis of the data can also show where the ship should go to gather more data in a particular area.
Once the survey is complete, the software can be used to generate interpolated grids of ASF data — the most convenient and accurate form of ASF data storage.
It is important with any scientific or engineering measurement to establish the error on that measurement. The same can be said of ASFs, and so the software can calculate the error bounds on ASF measurements. This “ASF error” data can again be published in grid form alongside the ASF database. This allows it to be used as one component of an Integrity Equation, implemented within the mariner’s receiver, to calculate Horizontal Protection Level (HPL).
After processing, the ASF data should be validated by performing a harbor approach or other maneuver that requires a particular positioning accuracy. For this, the software can be switched to “Validation” mode. Once the validation is successful, the data can be output in a publication format (RTCM SC-127 format for example).
The plot in Figure 2 shows part of an ASF database for Harwich and Felixstowe, major ports on the east coast of the UK. Using this data and DLoran in the Harwich and Felixstowe approach provides 10-meter (95 percent) positioning accuracy.
UK eLoran Prototype
This prototype eLoran system works alongside GPS. It has been in operation 24 hours a day since May 2010. It is “prototype” because it demonstrates the concept of eLoran using signals from existing Loran-C stations in Norway, the Faroe Islands, Germany, and France plus the UK’s station at Anthorn; see Figure 3.
Figure 3. Relevant European Loran-C stations for prototype eLoran.
These stations, together with ASF measurements and DLoran, can deliver a high-precision eLoran service in ports where 10-20 meter accuracy is needed, across the area enclosed by the green contour in Figure 4.
Figure 4. Coverage of prototype eLoran over the UK and Ireland.
It is very impressive, yet the full availability and accuracy benefits of eLoran are still to come as these stations are eventually upgraded to full eLoran capability. And for the last year or so, the GLA have begun to move beyond the confines of the Harwich and Felixstowe approaches and implement initial eLoran services in other regions around the GLA service area.
The GLA aim to do this in two stages. In the first stage Initial Operational Capability (IOC) service will be installed by mid-2014, with the second stage Full Operational Capability (FOC) service covering all major ports in the UK and Ireland, plus Traffic Separation Schemes, installed by 2019 or so in time for e-Navigation.
Initial Operational Capability
IOC involves upgrading the installation at Harwich and Felixstowe and new installations in the approaches to another six of the busiest ports in the UK: Aberdeen, Grangemouth, Middlesbrough, Immingham, Tilbury, and Dover. For each of these areas an ASF survey and a DLoran reference station will be required.
The corrections for these reference stations will be broadcast using the Anthorn Loran Data Channel. There is also the need for a Monitoring and Control System for the network of DLoran Reference Stations, and it is envisaged that this will be based in Harwich. Figure 5 illustrates the architecture of the Initial Operational Capability system. The diagram shows the major components: eLoran transmitter, DLoran reference station network, monitor, and control system. Also shown are the interfaces between the components, which provide not only operational data but also include the ability to monitor the integrity of the system. Also note that the Loran Data Channel is capable of supporting third-party messaging applications using a client “logon” facility. This is already being done at Anthorn.
Figure 5. The architecture of the UK GLA’s eLoran Initial Operational Capability.
The European tender process for seven operational reference stations and the control system is almost complete.
The aim of IOC is to provide areas for demonstrations and trials, so that the mariner can gain experience of the system and its capabilities and provide feedback to the GLA on its performance.
eLoran at the Port of Dover
In the absence of the final operational reference stations, the GLA decided to perform an early implementation using prototype equipment that was already available at the GLA. The choice for this implementation was obvious: the iconic Port of Dover, a major port on the southeast coast of the UK and the Dover Strait, one of the busiest seaways in the world. Some 500-plus vessels travel through the Strait each day on their way to or from the North Sea region; see Opening Figure.
The GLA have, with the agreement of Port of Dover Operations, installed a prototype DLoran Reference Station within the port’s Terminal Control building. The roof of the building is an ideal location for the reference station receiver antenna as the location demonstrates low noise in the eLoran band and has easy access to mains power, cable runs, antenna mounts, and Internet access.
The ASF survey took place in March 2012, and covers the area outlined by the yellow polygon in Figure 6.
Figure 6. Area of March 2012 ASF survey.
Accuracy Performance Validation
Once the ASFs had been measured and the prototype reference station installed, the performance needed to be tested. This was accomplished through a validation run of the vessel through the area.
Figure 7 shows a screenshot of the GLA ASF measurement software running in validation mode. The colored track shows the path of the vessel, with the color indicating the positioning error compared to differential GPS. The vessel travels through an area of extrapolated and interpolated ASF data, so the positioning error at the northern end of the track is higher than the lower end of the track.
Figure 7. Screenshot of GLA ASF measurement software running in validation mode.
Figure 8 shows a comparison of eLoran positioning against DGPS positioning along the route as a scatter plot. The associated Cumulative Distribution Function (CDF) is shown on the right of the diagram. From this it can be seen that the positioning accuracy obtained along this particular route was 12.5 meters (95 percent).
Figure 8. eLoran positioning accuracy scatter plot and cumulative distribution function of positioning error. Accuracy: 12.5 m (95%)
Dover to Calais Ferry Installation. Further validation and demonstrations will take place aboard a cross-Channel ferry. P&O Ferries in the UK has installed a receiver aboard their vessel, The Spirit of Britain. This relatively new vessel is one of the largest passenger ships to operate along the iconic Dover to Calais route. Data will be collected and feedback obtained on the eLoran service’s performance over the coming months.
Other Areas
The GLA continue their work towards IOC-level eLoran. Dover was the first port of call for the GLA eLoran Initial Operational Capability — the ASFs have been mapped and a prototype DLoran reference station has been installed. The final operational DLoran reference stations should be available this time next year.
The next area the GLA have concentrated upon is the Thames Estuary up to Tilbury. Although the GLA have not yet installed a permanent DLoran reference station, the ASF survey was performed in November 2012 using a temporary reference station installed at Medway. Along the route shown in Figure 9, a validation trial demonstrated 8.3 meters (95 percent) accuracy (Figure 10). The GLA have also recently surveyed the River Humber, including its approaches, up to the port of Hull. The data is currently in the process of being validated.
Figure 9. ASF map validation route from the port of Medway heading out of the River Thames estuary.Figure 10. eLoran positioning accuracy scatter plot and cumulative distribution function of positioning error. Accuracy: 8.3 m (95%).
Status and Next Steps
The next steps are to continue the implementation of IOC eLoran at the remaining port approaches for this phase. It is the aim that all ASF surveys will have been performed by the middle of 2014 in readiness for the installation of the operational DLoran reference stations at each candidate port. Licence agreements are being established with the various port authorities involved in order to allow this.
All ports that have been approached are positive and are keen to assist in the GLA eLoran implementations. eLoran noise surveys have been performed at all ports and locations for all DLoran reference stations have been found.
The Port of Dover has prototype eLoran up and running and has demonstrated 12.5-meter (95 percent) accuracy during the limited validation performed so far; however, further validation continues aboard the Spirit of Britain ferry.
The Thames Estuary ASF Survey has been performed, and 8-meter (95 percent) accuracy has been demonstrated in the area. The River Humber and its approaches have also been surveyed with validation in progress.
IOC-level DLoran reference stations should be available mid-2014, ready for installation.
The methods and processes employed during this work will be proposed for inclusion within the next version of the eLoran receiver Minimum Performance Specification as determined by Radio Technical Commission for Maritime Services (RTCM) Special Committee 27. These include techniques and algorithms used for ASF measurement processing, the preferred ASF file format, guidelines on the usage of ASF data, and integrity computation.
Acknowledgments
The GLA acknowledge the assistance of the crew of THV Alert, the Dover Harbour Board, Peel Ports (Medway), Associated British Ports (Humber), Aberdeen Harbour Authority, Forth Ports, PD Ports (Middlesbrough).
This article is based on a presentation made at the Institute of Navigation International Technical Meeting, January 2013, in San Diego, California.
Paul Williams is a principal development engineer with the Research and Radionavigation Directorate of the GLA, and technical lead of the GLA’s eLoran Work Programme, responsible for the ongoing roll-out of the GLA’s eLoran Initial Operational Capability (IOC). He holds a Ph.D. in electronic engineering from the University of Wales.
Chris Hargreaves is is a research and development engineer with the Research and Radionavigation Directorate Directorate of the GLA. His work focuses on eLoran in measurement trials, software development, and data analysis. He holds a masters’ degrees in mathematics and physics from the University of Durham and in navigation technology from the University of Nottingham.
The General Lighthouse Authorities of the UK and Ireland (GLA) have announced that ships in the Port of Dover, its approaches and part of the Dover Strait can now use eLoran radio navigation technology as a backup to satnav systems like GPS and Galileo. What is considered the world’s busiest shipping route is the first to deploy eLoran to counter jammers and space weather, the GLA said in a statement.
The ground-based eLoran system provides alternative position and timing signals for improved navigational safety. The Dover area, the world’s busiest shipping lane, is the first in the world to achieve this initial operational capability (IOC) for shipping companies operating both passenger and cargo services.
Today’s announcement represents the first of up to seven eLoran installations to be implemented along the East Coast of the United Kingdom. The Thames Estuary and approaches up to Tilbury, the Humber Estuary and approaches, and the ports of Middlesbrough, Grangemouth and Aberdeen will all benefit from new installations, and the prototype service at Harwich and Felixstowe will be upgraded, the GLA said.
Although primarily intended as a maritime aid to navigation, eLoran could become a cost-effective backup for a wide range of applications that are becoming increasingly reliant on the position and timing information provided by satellite systems.
“Our primary concern at the GLA is for the safety of mariners,” said Captain Ian McNaught, Chief Executive of Trinity House. “But signals from eLoran transmitters could also provide essential backup to telecommunications, smart grid and high frequency trading systems vulnerable to jamming by natural or deliberate means. We encourage ship owners and mariners to assess eLoran in this region and provide feedback to the GLA on its performance.”
P&O Ferries has installed an eLoran receiver on its new vessel Spirit of Britain. She will be based at Dover and is one of the largest passenger ships the busy Dover/Calais route has ever seen.
“Accurate real-time positional information is essential for the safe navigation of ships with modern electronic charts,” Captain Simon Richardson, head of Safety Management at P&O Ferries, said. “Satellite navigation systems are vulnerable to degradation of signal strength and our ships have also experienced occasional loss of signal. We welcome the development of a robust alternative to provide redundancy in real-time positional information and we see eLoran as the most effective solution to countering the problem.”
Commenting on the announcement Stephen Hammond, Minister for Shipping, said, “I congratulate the General Lighthouse Authorities on this initiative that seeks to improve navigational safety in what is the busiest shipping channel in the world, through the development and deployment of technology. I look forward to receiving reports of its effectiveness.”
As result of a Cooperative Research and Development Agreement (CRADA) between the U.S. Coast Guard and UrsaNav, Inc., on-air tests are being conducted from the former Loran Support Unit site in New Jersey.
One of the CRADA’s goals is to research, evaluate, and document a wireless technical approach as an alternative to GPS for providing precise time. The ability to obtain precise time to at least one microsecond is necessary for the proper operation and functioning of many critical industries and systems. Examples include telecommunications networks, banking and finance, energy and power delivery, emergency services, transportation systems, and military and homeland security systems.
Additional on-air tests are planned at various sites throughout the United States. Broadcasts will test several different frequencies, waveforms, and modulation techniques using evolutionary, state-of-the-art technology. Reception of these broadcasts are planned at both on-shore and off-shore locations, and will include advanced LF data delivery techniques. The results of these trials will be presented at national and international conferences. Parties interested in any part of the trial, or interested in doing their own measurements, are invited to contact UrsaNav.
The company has partnered with precise-time synchronization company Symmetricom and Nautel, supplier of high-power RF transmitters. According to UrsaNav, this “alliance of expertise” provides the foundation technology for a wide-area, terrestrial-based alternative to satellite systems such as GPS, GLONASS, and Galileo.
“Global government, industry, and academic experts recognize that advanced LF signals, of which eLoran is just one example, can provide alternative timing — either as a stand-alone service, or as a component of an existing positioning, navigation, and timing (PNT) service. The high-power, virtually jam-proof and spoof-proof LF signals operate independently of GPS and GNSS, and provide a Universal Coordinated Time (UTC) time reference in the order of tens of nanoseconds. The recognition of the criticality of time to many aspects of our national critical infrastructure has led to establishment of the CRADA to evaluate the benefits of an LF wide-area timing system.”
The LF signals can also be used as pseudoranges mixed in with GPS, or if enough transmitters are available, as a fully independent PNT network. In other words, a true backup PNT capability for safety-of-life navigation, for dispatching first responders, and for supporting critical national infrastructures.
First Galileo PRS Signal Received
Septentrio and QinetiQ, in close partnership with the European Space Agency (ESA) and their industrial partners, achieved the first successful reception of the encrypted Galileo Public Regulated Service (PRS) signal from the first Galileo satellites, launched in November 2011.
The signal was received on the Galileo PRS Test User Receiver (PRS-TUR) jointly developed by Septentrio (Leuven, Belgium) and QinetiQ (Malvern, United Kingdom) under an ESA contract. For the reception test, the receiver was installed in the Galileo Control Centre in Fucino, Italy, and operated by technical experts from ESA.
Septentrio and QinetiQ are long-term contributors to the Galileo Programme, working closely with ESA, the European GNSS Agency (GSA), and European industrial partners since 2003.
Count Five Compass IGSOs
The BeiDou-2/Compass G5 satellite launched on February 24 has achieved an initial approximately geostationary orbit.
The current sub-satellite east longitude is 57.23 degrees. The intended final orbital slot may be 58.75 degrees, one of the previously announced orbital locations and one used by the BeiDou-1 demonstration system.
The 2012 NextGen Plan specifically mentions GPS/GNSS as follows:
Performance Based Navigation (PBN). The current aircraft fleet is well equipped with PBN capability. In the air carrier community, the heart of the PBN capability is the Flight Management System, which uses input from multiple distance measuring equipment (DME), or from the GNSS using a GPS sensor or a GPS with Wide Area Augmentation System (WAAS) sensor.
Ground Based Augmentation System Landing System (GLS) Enabler. This program researches use of differential GPS corrections to support Category III (Cat III) approaches. This capability will be the same as Cat III instrument landing system (ILS), without the need to restrict taxiing aircraft near antennas and at reduced cost to the FAA.
Automatic Dependent Surveillance–Broadcast (ADS-B). Aircraft position (long-lat, altitude, and time) is determined using GPS, an internal inertial navigational reference system or other navigation aids. ADS-B Out involves transmission of a GPS position (or of comparably performing navigation equipment meeting integrity and accuracy requirements) from an aircraft to display its location to controllers on the ground or to pilots in other aircraft equipped with ADS-B In.
Low-Visibility/Ceiling Approach.Localizer Performance (LP) with Vertical Guidance (LPV) Approaches. These are more cost-effective to implement compared to additional ground-based navigation aids (NAVAIDs) and their approach procedures. Increasing the number of LPV/LP approaches will provide further incentives for users to equip with GPS/WAAS. This will provide increased utility to the more than 40,000 general aviation aircraft that are already WAAS-capable. The FAA will also deliver LP approaches to runways that do not qualify for LPVs due to obstacles.
Ground Based Augmentation System (GBAS) Precision Approaches. GPS/GBAS support precision approaches to Cat I and eventually Cat II/III minima for properly equipped runways and aircraft. GBAS can support approach minima at airports with fewer restrictions to surface movement and offers potential for curved precision approaches. GBAS may also support high-integrity surface movement requirements.
— Bill Thompson, GPS World aviation editor
LightSquared-Sprint Contract Terminated
Business Case for GPS Threat Gone Away
The principal business prop under the LightSquared plan for ancillary terrestrial component (ATC) broadcast of a powerful signal that would have disrupted GPS operations dropped out from under the company on March 16, as wireless carrier Sprint terminated its $9 billion agreement with LightSquared. LightSquared had several such partnership agreements, but the Sprint deal was the largest, and in many eyes the driver of the aggressive plan. With it gone, LightSquared’s other deals will likely dissipate — and the current threat, at least, to GPS industry and users should effectively go away.
Sprint has apparently concluded that LightSquared has no prospect of reversing the revocation of its conditional waiver last month by the Federal Communications Commission, as a result of extensive testing conducted by the company, various government agencies, and the GPS industry. Earlier, Sprint had twice extended its tentative agreement with LightSquared as the tests took place over the last year, but reached the end of its road March 16 — which is also the last day the FCC is accepting public comments on its decision to revoke the waiver.
An official LightSquared statement said termination of the Sprint agreement was “in the best business interests of both companies, and was not unexpected given the regulatory delays.” Sprint will return $65 million in prepayments that LightSquared made to Sprint.
Some analysts have predicted that LightSquared may be forced to sell off its assets by the end of the year. Among these assets are the spectrum licenses for the lower LightSquared band (1526–1536 MHz), the so-called Low 10, and the higher band (1545-1555 MHz), known as the Upper 10, adjacent to GPS L1. These bands have a history of trading hands as their owners go into bankruptcy or otherwise out of business.
The next touchpoint of concern for the GPS community is the outcome or perhaps various outcomes of the FCC workshop on spectrum efficiency and receivers that took place March 12–13. The workshop was convened to discuss the characteristics of receivers and how their performance can affect the efficient use of spectrum and opportunities for the creation of new services, according to the FCC.
The first part of the recent UrsaNav press release says it best:
This week for the first time since August 2010 advanced low frequency (LF) signals, including a new eLORAN, are on the air in North America! As a result of a Cooperative Research and Development Agreement (CRADA) between the United States Coast Guard (USCG) and UrsaNav, Inc. live testing of a wide-area precise timing solution has begun. These initial tests include a comprehensive pallet of signals, including eLoran, that are being evaluated for their ability to provide a robust, wide-area, wireless precise timing alternative that can operate cooperatively with GPS, or during periods of GPS unavailability.
Why eLORAN
Global government, industry, and academic experts recognize that advanced LF signals, of which eLORAN is just one example, can provide alternative timing — either as a stand-a-lone service, or as a component of an existing PNT service. The high power, virtually jam proof and spoof proof LF signals operate independently of GPS and GNSS, and provide a Universal Coordinated Time (UTC) time reference in the order of tens of nanoseconds. The recognition of the criticality of time to many aspects of our national critical infrastructure has led to establishment of the CRADA to evaluate the benefits of an LF wide-area timing system.
UrsaNav on-air eLORAN tests continue at various sites throughout the United States (CONUS and Alaska). Broadcast demonstrations will test several different frequencies, waveforms, and modulation techniques using evolutionary state-of-the-art technology.
Reception demonstrations of the eLORAN broadcasts are planned at both on- and offshore locations, and will include advanced LF data delivery techniques. Trial results will be presented at national and international conferences. Anyone interested in any part of the testing or interested in making their own measurements are invited to contact UrsaNav.
UrsaNav eLORAN system. Arthur Helwig (UrsaNav) and
Aaron Grant (Nautel) prepare the LF transmitter for the next
set of on-air tests.
Partnered with Symmetricom and Nautel, UrsaNav says it has the world’s most advanced LF alternate PNT and data solutions to include the world’s best high-performance eLORAN timing receivers. UrsaNav has partnered with two of the best in the business for timing and transmitters, and this alliance of expertise provides the foundation technology for the best wide-area terrestrial-based alternative to GNSS such as GPS, GLONASS, and Galileo.
That being said, I would add that you should not only consider the UrsaNav LF system as an alternative, but during normal GPS operations as a complimentary and/or augmentation to GPS, and then as a back-up and integrity system when the situation warrants.
As one of my professional colleagues, who is a retired USCG officer and once ran the USCG Navigation Center, stated, “This is a big deal! It is in fact the first and biggest piece of good news about a true PNT (position, navigation, and timing) backup for GPS since Loran-C was killed in the FY2010 budget.
“Not only is this an independent timing backup, but the LF signals can also be used as pseudoranges mixed in with GPS, or if enough transmitters are available, as a fully independent PNT network. In other words, a true backup PNT capability for safety-of-life navigation, for dispatching first responders, and for supporting critical national infrastructures.”
This is a pretty enthusiastic response, even from a LORAN aficionado, and it is indicative of the responses I received whenever I reached out for comments from knowledgeable PNT SMEs (subject matter experts) around the globe.
The response nationally and internationally has been extremely positive as well — especially in light of the recent LightSquared debacle and the now better-understood vulnerabilities of the very low-power GPS signals.
I hoped I would never have to type or have you read that word again, as a noun or a verb, but the whole LightSquared scenario did serve to point out a dire need and shortcoming in the U.S. PNT infrastructure. Fortunately, the proposed UrsaNav eLORAN system appears to be on track to fill that need perfectly.
For the first 32 years that GPS signals were broadcast, LORAN-C served as a critical backup for timing and a less accurate but viable alternative for navigation. In fact, Loran-C, along with GPS and cesium clocks synchronized to UTC, were the only accepted Stratum 1 frequency sources at the time (Stratum 1 frequency sources provide a minimum frequency stability of 1 x 10-11 per day.). Then in 2010 the current U.S. administration was looking for government programs to cut and for some unknown reason they latched onto LORAN-C, which was in a critical state of transition at the time.
LORAN-C has been around since World War II. I among many other aviators used it extensively in Vietnam, and frankly for many countries and users today it is still a totally adequate service. With USCG expertise and support for 52 years, LORAN-C provided unparalleled timing and navigation services around the United States and Canada until the pretender known as GPS came along and dethroned the aging monarch.
Now, that may sound like a natural sequence of events, except that LORAN-C was in metamorphosis, 80% of the way through the process actually, of morphing into a new digital (1990s era technology) LORAN know as eLORAN or enhanced LORAN with better, more reliable transmitters, smaller receivers, and a virtually jam-proof signal structure. Many likened the legacy eLORAN to a strong ground-based GPS with coded signals for security. All that was in place and 80% complete when the whole process was killed by an administration with a strong Luddite orientation and subsequently the bean counters pulled the plug in 2010, despite recommendations to complete eLoran from both the Department of Transportation’s Positioning and Navigation (PosNav) Committee and the Department of Homeland Security Geospatial Committee and the strong personal support of the DOT Undersecretary for Policy and the DHS Deputy Undersecretary for Preparedness and National Protection and Programs. My sources tell me the Office of Management and Budget (OMB) was determined to do away with Loran-C and facilitated its ultimate demise. An unfortunate theme we have seen played out much too often: Non-technical people forcing ill-advised technical decisions. In a country whose greatness has always been its technical acumen, willingness to take risks, and self-assurance, OMB stands as a chilling element of focus today…but, that’s a subject for a future article.
Since that time the U.S. Coast Guard spent more money dismantling the legacy LORAN-C infrastructure and antennas than it would have taken to complete the 20% upgrade for a full transition to eLORAN. Taking down the Port Clarence, Alaska, tower, the video of which was a YouTube favorite for many weeks, cost an estimated $8 million. The destruction of the towers in Attu (right), Shoal Cove and St. Paul were probably on average $5 million each. With the tower removal in Baudette, Minnesota, the cost of removing Loran towers to date cost close to $25 million. One could argue that the administration created some jobs in these “shovel-ready” tower tear downs, but I have no doubt that a better use of the funding would have been to deliver a robust positioning, navigation, and timing backup for the nation. But alas that is ancient history in the technology world, a whole 18 months to be exact.
Then along comes the Lone Rang… I mean Chuck Schue, the CEO and president of UrsaNav, which is a small company originally founded by Charles “Chuck” Schue, because frankly he has always been interested in navigation. Chuck is a former ION (Institute of Navigation) Washington, D.C., Section Chair and is a current member of the ION Council. Chuck is also a retired USCG officer and his last job in the USCG was as Commanding Officer of the Loran Support Unit, providing direct support to a large portion of the functions supported by the USCG Navigation Center (NAVCEN). So it is no accident that Chuck and UrsaNav saw the gaping hole for GPS support that was created when LORAN-C and the legacy eLORAN programs were unceremoniously put on the chopping block. Now UrsaNav with their new 2012 version of eLORAN and the help of the USCG, through a CRADA, have stepped in to fill a very real need.
In my opinion (pun intended) their timing could not have been better. LightSquared is hopefully behind us along with the threat of losing GPS capabilities and all GPS P&T (positioning and timing) enables without a viable backup. This is definitely not a scenario any sane person wants to see happen again and fortunately UrsaNav LF timing and eLORAN can provide a critical back-up, augmentation and integrity check while simultaneously providing the USG with a security blanket, as Linus would say.
The USCG-UrsaNav CRADA
Before considering reactions from other USG agencies and then international reactions to the UrsaNav program, maybe it would be best, in case any of you are wondering, to describe the function of the subject CRADA since it has been mentioned several times.
In February 2012 the U.S. Coast Guard Research & Development Center (R&DCEN) announced it had entered into a Cooperative Research and Development Agreement (CRADA) with UrsaNav to research, evaluate, and document at least one alternative to the Global Positioning System (GPS) as a means of providing precise time. The alternative under consideration is a wireless technical approach for providing precise time using U.S. government facilities and frequency authorizations.
While this is a very general statement and does not give much away, it is meant to be that way since it is, after all, an R&D effort and general statements give you the most leeway when considering options and trade space.
CRADAs are authorized by the Federal Technology Transfer Act to promote the transfer of technology to the private sector for commercial use as well as specified research and/or development efforts that are consistent with the mission of the federal parties to the CRADA. The federal party or parties (USCG) agree with one or more non-federal parties (UrsaNav) to share research resources, but the federal party does not contribute funding.
This means that the USCG and UrsaNav are sharing R&D efforts, data, and even non-monetary resources, but the USG is not providing any funding to UrsaNav for the project. So UrsaNav is footing the bill; at the same time, it has access to USG data and resources, to include buildings and transmitting towers, for example, and UrsaNav knows it has at least generated interest among government and commercial users for LF timing signals.
DOT/FAA Reactions
When I first saw the UrsaNav announcement, I immediately thought of the DOT and FAA, since they have been trying to think of ways to provide a common, non-GNSS, distributed timing backup for all their facilities and customers as part of their efforts to develop an alternate PNT (APNT) capability. One of the APNT alternatives is considering distributing time to air traffic control facilities and aircraft through their ground-based DME (distance measuring equipment) facilities. For the non-aviators among you, DME signals allow aircraft to determine their distance from a DME location. Properly equipped aircraft (primarily commercial and high-end general aviation) can use ranging from multiple DMEs to actually determine their position and follow area navigation (RNAV) procedures for more effective routing and flexibility. In order to utilize the DMEs as a ground-based, high-power (1000 W) equivalent of a satellite constellation will require each DME facility to be synchronized in time to around 30 nanoseconds or better. Now, with the possibility of an eLORAN time standard with a huge booming, virtually jam-proof and spoof-proof signal, across the CONUS and Alaska, this FAA alternative solution could be greatly facilitated. While the FAA also has the option to use GPS time, or time from its own WAAS ground-based clock ensemble, or WAAS retransmitted time combined with GPS time for remote locations and to back it all up and provide an integrity check, the availability of an eLoran alternative is certainly worthy of FAA APNT consideration. The FAA’s distribution problems would be solved, and since both GPS and eLORAN have the capability for encoded signals, the integrity (information assurance) and security problems are solved as well. Comparison of the vulnerable GNSS signal with the robust eLoran timing signal could alert an operator to possible spoofing or even a less sinister loss of integrity event. So this is a win/win for the FAA and several other critical national agencies and infrastructures that must remain nameless for security purposes.
International Partners
What makes the UrsaNav solution so promising and frankly exciting is that they are not conducting these experiments and demonstrations in isolation. For the past few months UrsaNav has been working with the Lighthouse Authorities of the United Kingdom and Northern Ireland as well as Chronos Technology, a world leader in GNSS jamming and interference detection, in Great Britain. To determine how the UrsaNav eLORAN program is progressing internationally, who are you going to call? Personally, if it concerns GPS, time, and the UK, there are two people who immediately come to mind: Dr. David Last and Martin Bransby.
Professor David Last is a consultant engineer and internationally renowned expert witness specializing in radio navigation and communications systems. David is a Professor Emeritus (that means he is at least as old as I am) at the University of Bangor, Wales, and Past-President of the Royal Institute of Navigation (RIN), the equivalent of the U.S. ION, but RIN has only been around since 1947. David acts as a consultant on radionavigation and communications to companies and to governmental and international organizations worldwide and is active as an expert witness, especially in forensic matters concerning GPS.
Both David and Martin are highly qualified SMEs and BLUF, or bottom line up front; their praise for the UrsaNav initiative could not be higher.
According to Professor Last, “…a ‘sky-free’ timing service like the one UrsaNav will hopefully soon be radiating in the United States is already available across the British Isles and adjacent parts of Europe. The eLORAN system uses the GLAs’ prototype eLoran system plus GPS/eLoran timing receivers from UrsaNav and Chronos Technology.
“The prototype eLoran service has been running 24/7 since January 2008, serving the eastern half of Britain and the North Sea. It now delivers 10-meter (~30 feet) navigation accuracy in the approaches to Harwich and Felixstowe, the UK’s major container ports, where a prototype full differential service has been in place since mid-2010.
“In addition, the UK transmissions support a prototype robust, nationwide data channel that will benefit in future from the techniques currently being developed by UrsaNav to expand the data capacity of eLoran-compatible LF transmissions.
“This is all part of the resurgence of terrestrial LF services in response to the vulnerability of GPS and all other GNSS (read LightSquared). The GLAs are leading this movement to adopt eLoran as the terrestrial complement at sea and supporting the use of the new eLoran transmissions for sky-free complementary navigation, timing, data, and tracking of land vehicles. And the neat thing about LF timing and data is that a single station serves a large area. So the UK station delivers data across the UK and timing even more widely. This appeals to all sorts of folks who aren’t interested in navigation. But once enough timing and data stations are on the air, you get back navigation!”
Now, Martin Bransby is the R&RNAV (Research and Radionavigation) manager for the General Lighthouse Authorities (GLAs) of the UK & Ireland. Which simply means he is a senior engineering manager and program manager with extensive experience in R&D of highly technical assets, such as maritime aids to navigation, radar, C4ISTAR, and tactical data links, and he is the official GLA POC working the eLORAN program in the UK and Ireland, which he indicates is progressing extremely well. So well, in fact, the GLAs awarded a 15-year contract to provide a state-of-the-art eLORAN service to improve the safety of mariners in the UK and Western Europe. The service contract includes R&D work and the operation of an eLORAN service through 2022.
Support: The Good News
Back on this side of the pond, my sources at the USNO (U.S. Naval Observatory) our resource for Coordinated Universal Time or UTC are supportive of the UrsaNav eLORAN effort. A senior source, who prefers to remain anonymous, stated that the USNO will support any USG terrestrial time distribution system that may emerge from the UrsaNav eLORAN effort by providing the underlying timing reference “UTC (USNO).” However, to achieve true GPS independence, my source would like to see either fiber-optic or two-way satellite time transfer (TWSTT) utilized to sync the eLORAN ground transmitters. And in the end higher power, GPS independence, and good indoor reception are probably the greatest advantages. My source is looking forward to the results of this initial demonstration by UrsaNav and the USCG.
According to Chuck Schue, UrsaNav, anticipated this USNO preference and is working with Symmetricom on a TWSTT while also developing a TWLFTT, or two-way low-frequency time transfer capability, which allows for time transfer from a UTC source such as USNO or NIST that is completely sky-free.
The Bad News
We’ve all heard the Biblical phrase that originated in Matthew concerning “the right hand not knowing what the left hand is doing.” In this instance, where eLORAN is concerned, the USCG may have adopted that as a program motto.
Note: The real motto of course is Semper Paratus, and the brave men and women of the USCG live up to it everyday.
Originally in the Unites States, CONUS, and Alaska, there were 24 LORAN-C transmitters with towers between 600 and 1350 feet tall; add the towers supporting the Joint U.S.-Canadian LORAN-C system plus the LORAN-C Support Unit tower, and there were a total of 30 huge LORAN-C towers with all the accompanying support structures for the transmitters, support crews, etc. Today, there are only 25 towers remaining — as the USCG engineers are in the process of dismantling the LORAN-C infrastructure — five towers in the last 18 months.
As often happens in a large distributed organization, though Headquarters (CG-5) supports the eLORAN CRADA with UrsaNav and fully realizes that future eLORAN deployment depends on reuse of existing infrastructure, the civil engineering support organization gets its money and develops its project lists separately. Consequently the antenna towers at Attu (located at the end of the Aleutian chain) and Port Clarence (situated well north of Nome) have come down, as have the towers in St. Paul (in the Pribilof Islands, northern Bering Sea) and Shoal Cove (located in SE Alaska, near Ketchikan). Only two towers remain in Alaska; one in Kodiak (adjacent to the USAF-Alaska launch facility) and one at Tok Junction (on the ALCAN Highway, southeast of Fairbanks). Within CONUS, the USCG engineers are in the process of dismantling the facilities in Baudette — which is just about as isolated as some of the sites in Alaska.
Operational Issues
The operational problem is that while the much more powerful and economical energy-scavenging transmitters from UrsaNav’s partner Nautel, and new wave forms being produced by UrsaNav, probably only need to utilize 8-10 towers — the system is that much better and more powerful — no one knows where they need to be located until more tests are conducted. So how do the USCG engineers know which ones to dismantle? Obviously they don’t and there’s the rub, plus if the system is really successful and the data portion is a success, there could be a need for even more towers. Solution — the R&D guys (RH) need to coordinate with the engineering crews (LH) and put a hiatus on dismantling LORAN-C towers and the associated infrastructure, unless they pose a safety hazard, until the outcome of the CRADA and subsequent acquisition decisions have been made.
Seriously, the USCG and UrsaNav are heroes for initiating the CRADA, and my hat is off to them for realizing the critical need for eLORAN, but seriously, somebody pick up a phone and call the engineers, call the Commandant, call somebody that can put the tower demolitions on hold.
The bottom line is UrsaNav and the USCG are to be congratulated for their foresight and planning. Let’s hope the eLORAN demonstrations continue to be successful and that a contract is forthcoming quickly before we, and the powers that be, forget the LightSquared lessons learned…like we would ever let that happen.
All in all, this is a win/win proposition for the USCG, the USG, and for GPS users everywhere. Stay tuned for more on this topic.
While you are reading this I will be attending the Munich Satellite Summit in Germany, so guess what my topic will be next month?
Many maritime users today believe that GPS will always be available. This is simply not the case.
By Alan Grant, Paul Williams, George Shaw, Michelle De Voy, and Nick Ward, The General Lighthouse Authorities of the United Kingdom and Ireland
GNSS availability can be affected in many ways, through events or conditions that affect constellation health, the signal-in-space, or the reception of that signal. The primary means of positioning, navigation, and timing (PNT) employed in maritime applications, whether stand-alone or augmented, has well known vulnerabilities.
This article considers three specific threats and reports on how they may affect maritime safety: GNSS interference and jamming; constellation availability; and space weather events.
Interference and Jamming
There has been a marked increase in both the use and the availability of GPS jamming equipment in recent years. The implications are that jamming units may find their way onto ferries and around ports or harbors where they will interfere with the many systems utilizing GPS, thus affecting maritime safety.
GPS jamming units are widely available on the Internet, with current models already capable of jamming L1, L2, and L5 signals. While we report here on the jamming of GPS, all GNSS constellations would be affected in a similar manner.
To understand the effects of jamming and GPS service denial on maritime safety, the General Lighthouse Authorities of the United Kingdom and Ireland (GLAs) conducted two jamming trials, in collaboration with the UK Government’s Ministry of Defence (MOD), who provided and operated the GPS jamming units. For the safety of all GPS users, and in line with MOD regulations for the peacetime use of GPS jamming units, notice was given to all national bodies. In addition, the GLAs issued notices to mariners explaining that aids to navigation (AtoNs) using GPS in the vicinity of the trials location would be unreliable during the jamming periods.
Flamborough Head. The first jamming trial was conducted off the East coast of the United Kingdom near Flamborough Head. The aim of this trial was to understand the effect GPS jamming may have on ship-borne and shore-based equipment, GLA AtoNs, and also on the crew.
The Northern Lighthouse Board vessel Pole Star steamed between two known waypoints, through an area affected by the jamming signal. Data was recorded from two typical marine-grade GPS receivers installed on the vessel, along with an eLoran receiver that provided the true position throughout the trial.
The results identified three distinct states (Table 1) corresponding to the manner in which GPS-fed equipment responded to jamming conditions. When the jamming signal was sufficiently strong to prevent reception of GPS signals, a large number of alarms sounded on the bridge almost simultaneously, providing a potentially disconcerting and confusing environment for the mariner. However, the effect that represented the highest risk was the provision of erroneous data from some GPS receivers.
Table 1. Effects observed for the three states identified from Flamborough Head trials.
Figure 1 compares an erroneous position reported by a typical marine-grade GPS receiver with the vessel’s true location. In this figure, the light blue line shows the path taken between the two waypoints.
The colors of the plotted position points indicate vessel speed. The three states described in Table 1 can be seen.
State 1 is observed at either end of the passage where the solid blue line occurs; this is where the jamming signal strength is much lower than the GPS signal strength, and the GPS-fed systems are operating normally.
As the vessel approached the main lobe of the jamming signal, indicated by the red lines, it reached an area where the jamming signal was comparable with the received GPS signals, leading to State 2. During this state, erroneous data can be observed with the receiver reporting the vessel on land traveling at high speed.
As the vessel entered the main lobe of the jamming signal, State 3 was observed: the GPS signals were swamped by the jamming signal, and the receivers failed to provide an output. Then, as the vessel continued the passage out of the jamming area, one can observe the change in states as the ratios of jamming to GPS satellite signals decrease, and GPS is reacquired.
In the worst case, the GPS receiver reported a position some 22 kilometers away from the true location. The GPS receiver nevertheless declared the position valid. This position was made worse by the fact it was reported inland at a speed of more than 100 knots, while the trial vessel steamed steadily at 10 knots. Depending on how the resulting GPS positioning data is used, it could feasibly result in vessels changing course, through the use of an autopilot, and it could also affect the vessel’s reported position to the outside world. This would then not only affect the vessel’s situational awareness but also the situational awareness of vessels in the vicinity.
The errors observed in Figure 1 were also seen on the vessel equipment fed by the onboard GPS receivers. Erroneous positions were observed on the vessel’s electronic chart display and information system (ECDIS), on the automatic identification system (AIS) positions (where loss of position prevents the unit from calculating a range or bearing to nearby vessels, greatly affecting the crew’s situational awareness), and on the vessel’s radar (Figure 2).
The results observed during these trials gave an important example of what can happen to onboard equipment as well as the impact it can have on the mariner during periods of GPS jamming and service denial. It is clear that GPS denial caused by jamming can not only prevent PNT information from being calculated, it can also result in erroneous data being presented to the mariner.
Newcastle. A second series of demonstrations was conducted off Newcastle-upon-Tyne, on the North East coast of England, to communicate the importance of resilient PNT to a selected audience. The audience included a number of key decision-makers from European and UK governments, maritime industry, mariners, and other aids-to-navigation service providers. The demonstrations took place onboard the Trinity House vessel Galatea.
For this trial, the GPS jamming unit was installed onboard the Galatea and configured to jam GPS within a small
area around the vessel. As before, two typical marine-grade GPS receivers were installed along with an eLoran receiver; for this trial, a modified electronic chart display was also installed and altered to enable two position inputs to be displayed at the same time, to compare the reported GPS and eLoran positions in real-time.
Throughout the demonstrations differential Loran (dLoran) corrections were provided using a transportable reference station installed on the shore at South Shields, to mitigate the impact of temporal variations on the eLoran position. Differential-Loran corrections were generated by the reference station and sent to the GLAs’ eLoran transmitter in Cumbria for inclusion in the eLoran Loran Data Channel (LDC) broadcast. The eLoran receiver on the vessel received the broadcast and was able to extract and apply the corrections in order to obtain an eLoran position within 9 meters (95 percent).
One demonstration scenario showed the sudden effect of a strong jamming signal, designed to simulate a jamming unit being brought onto a ferry or other vessel. This took the vessel’s equipment directly to State 3: complete loss of GPS information with a large number of alarms sounding on the bridge. The loss of GPS data prevented the Galatea’s AIS and VHF units, among other systems, from operating correctly.
Before the second scenario was conducted, the jamming unit was stopped, and all of the GPS receivers integrated into the bridge equipment were allowed to reacquire satellites and fully recover. The second scenario was designed to reflect a vessel steaming towards a jamming source. The field strength of the jamming signal was slowly increased until State 2 was observed, with erroneous and often hazardously misleading information reported.
As with the Flamborough trials, erroneous GPS positions reporting unfeasibly high speeds were observed as shown in the OPENING Figure. However, significantly more subtle errors were seen: errors where the vessel’s reported position differed only very slightly from the true location and wandered around slowly. These subtle changes produce believable positions but hazardously misleading information (HMI). While the overall result of GPS jamming on Galatea was consistent with that observed on Pole Star, there were a few marked exceptions.
The effect of GPS jamming can be seen (Figure 3) on the erroneous positions reported by the trial vessel NLB Pole Star (center right) and also on the vessel DutchProgress (top left).
The ECDIS onboard the Pole Star reported erroneous positions and ultimately failed with the complete denial of GPS. However the ECDIS on the Galatea continued to track the vessel’s position due to an additional position feed from the vessel’s gyro, making it more resilient to jamming, but only in the short term until the gyro requires re-calibration. This is carried out with its built-in GPS receiver! In addition, the AIS transceiver on the Pole Star reported the vessel’s position erroneously due to jamming, and this was observed at shore-based traffic monitoring stations.
During the demonstrations on the Galatea, the AIS transceiver did not provide any erroneous position information, as can be seen in Figure 4. These differences show that the impact of GPS jamming will be different for each vessel and depends on the model, installation, and configuration of the onboard systems.
Effect of Jamming on Safe Navigation
To navigate safely, the mariner needs reliable, clear and trusted information about where the ship is and what is going on around it, so that any threat can be located and identified. While consideration is often given to threats such as areas of shallow water, obstacles, or other vessels; consideration is not generally given to the loss of positional information, timing, or situational awareness.
Loss of GPS-derived PNT information at sea results in the loss of the vessel’s ECDIS, AIS, GPS, and DGPS receivers, preventing the mariner from being able to position the ship and others around it through what are nowadays regarded as the normal means. In addition, the systems one would normally expect to be independent from GPS, and as such available for use in GPS-denied conditions, are also affected; namely the vessel’s radar and gyro-compass.
The radar takes a GPS input to provide a “North-up” setting and the gyro-compass uses GPS to stabilize drift error. Under GPS-denial conditions these units also enter an alarm state and should not therefore be used in that condition.
Clearly GPS jamming can significantly affect the safety of mariners. From these trials it can be seen that the extent of the impact varies from vessel to vessel depending on the equipment installed and the configuration selected.
Satellite Constellation. From the users’ perspective, GNSS availability is the percentage of time they can receive usable data from sufficient satellites in order to calculate their position. The reduction in the number of available satellites in the constellation will have a direct impact on the system’s availability.
A report from the U.S. Government Accountability Office (GAO) in 2009 predicted “significant challenges in sustaining and upgrading widely used [GPS] capabilities” due to delays in launching modernized GPS satellites. The GAO reported the probability of maintaining a constellation of at least 24 usable GPS satellites could reduce to 80 percent or less by 2011, and not return to 95 percent probability consistently until 2015. This could lead to reduced satellite numbers causing coverage “windows” where less than four satellites could be observed and as such reduced GPS availability.
A later report by the GAO indicates that the probability of maintaining a constellation of at least 24 operational GPS satellites is now expected to be 95 percent for the foreseeable future. This figure is based on the current launch schedule, and although the U.S. Air Force Space Command (AFSPC) has provided reassurances, the satellite launch program has in recent years experienced delays, and therefore the risk of reduced satellite availability still remains.
Following the 2009 report, the GLAs commissioned a study to investigate the impact a reduced GPS constellation would have on users in their waters. This study was conducted by the GNSS Research and Applications Centre of Excellence (GRACE) and was split into two parts. The first part was to analyze the impact theoretically and found that with a 21-satellite constellation, GPS coverage “windows” (for example, fewer than four satellites) could last for several minutes and cover a large proportion of the UK and Ireland (Figure 5). This can cause reduced GPS availability and therefore increased likelihood of position errors affecting maritime safety.
The second part of the study investigated the effects further through a dynamic simulation, investigating the effects should a vessel be position
ed off the coast of Belfast during one of the coverage windows. For this a marine-grade GPS receiver and a simulator were used to observe the effects. The study found that the number of available satellites fell below four for several minutes and the reported position data from the receiver appeared to freeze for up to 10 minutes.
If a mariner was traveling at a speed of 35 knots when the position input froze, his reported position would be in error by 10 kilometers from an outage lasting 10 minutes. These outages are significant, and mariners need to be informed of such risks to GPS (and GNSS in the future) before they occur, so they are prepared for any disruptions.
Space Weather. Space-weather events are a particular concern to GNSS availability due to their random nature. It is known that GNSS signals are delayed proportionally to the number of free ions as they propagate through the Earth’s atmosphere enroute to the receiver. The amount of ions in the ionosphere, the total electron count (TEC), is dependant on time of day, latitude, and solar activity, among other factors. During high solar activity, the number of ions in the atmosphere is much higher than at any other time. The greater the signal delay, the larger the errors are in the satellite’s pseudo range and hence the position error can be significant.
Variation in electron density along the GNSS signal path causes signal refraction that produces phase scintillation, introducing group delay that may cause large errors in the pseudorange measurement. Diffraction of the signal wave front induces amplitude scintillation — variations in signal amplitude — with strong fades possible, leading to a GNSS receiver losing signal tracking, and at worst the GNSS navigation solution may be lost.
Solar activity is cyclical, peaking at a maximum approximately every 11 years, during which periods GNSS performance can be severely degraded, especially at equatorial, auroral and polar latitudes. The next solar maximum is predicted to occur during 2013.
During quiescent periods of solar activity, ionospheric effects on GNSS can be managed such that the residual errors caused by the ionosphere do not generally pose a problem to maritime navigation performance.
The GLAs’ DGPS corrections significantly reduce common mode errors, including the effects of the ionosphere. However, at the peak of the solar cycle with high levels of sunspot activity, solar storms and flares, the application of ionospheric models and differential corrections may be less effective, and this could increase position errors and introduce an integrity risk to maritime navigation.
Maritime navigation systems and services that rely on GNSS are at greatest risk of disruption from the ionosphere during the period from 2011 to 2015. Even during a quiet solar maximum, the occurrence of individual sun spots could produce significant effects for discrete events. The effects vary with latitude, season, and time of day (the hours soon after sunset being most affected).
Space weather events have the potential to affect GNSS availability, either by affecting the performance of the satellites themselves or by preventing signal reception.
Mitigation. In general, a number of steps can be taken to help reduce the impact of these threats:
Increase awareness of GNSS vulnerabilities.
Detect incidents and warn the mariner when they occur.
Prevent incidents from occurring, where possible, through legislation and enforcement.
Reduce as much as possible the effects of incidents when they occur, through the hardening of GNSS technology.
Have alternative means of PNT, independent of GNSS.
Understanding that these threats exist and knowing what disruption they may cause is the first step to mitigating their effects, but this does not stop them happening. Being able to identify that an event is occurring and that the data being received from the receiver may not be true is an important part of mitigating the effects.
For jamming issues specifically, the use of GPS jamming units is illegal in the UK and Ireland; however, preventing them from being used is very difficult to achieve. Jamming units are small and easily hidden; however, port-side security and vessel security procedures should prevent jamming units from being used in these locations.
It is a different case, however, to prevent a jamming unit from being used at a coastal location or headland due to the remote nature of these areas.
Mitigating the effect of jamming can be achieved in a number of ways: by limiting the effect within the receiver by using anti-jamming techniques, or by hardening GNSS receivers. Ultimately the best mitigating activity is to not rely on GNSS PNT once the integrity of the data has been compromised.
For space weather events or cases of reduced satellite numbers, there is very little action the mariner can take to remedy the problem or stop it happening. The mitigating action here is one of awareness — information forewarning the mariner that such a condition is imminent, for example.
Monitoring and detection networks can assist in providing such notifications and real-time information on GNSS problems. The need for such a network across the UK and Ireland is the subject of a different GLA publication, but the GLAs support the discussion on a body to monitor GNSS performance and to take the lead in the dissemination of key information.
For periods where GNSS availability has been affected by mutual interference, jamming, space weather events or constellation issues, the best mitigating action is to use PNT information from a second source, one with dissimilar failure modes.
Mariners need to be prepared for GNSS failures and have access to PNT information through dissimilar systems. In addition, procedures covering what to do in the case of GNSS unavailability should also be provided and rehearsed. It is with this view that the GLAs firmly promote the use of all available means of navigation.
Conclusions
All three threats to GNSS availability reviewed here could affect maritime safety. The two trials observed presentation to the mariner of erroneous data, some of which could be considered hazardously misleading, along with the degradation of crews’ situational awareness. The main effects observed were:
The presentation of random errors leading to hazardously misleading information that could, depending on installation, cause a vessel to move off course.
The presentation of erroneous and potentially misleading data to other vessels and shore-based infrastructure.
The sheer number of alarms on the bridge of the vessel could be disconcerting and distracting for the mariner.
The loss of GPS-fed systems, which can create an unfamiliar bridge situation and remove safety-critical systems from operation.
A large number of bridge systems are integrated with GPS and enter an alarm state during periods of GPS outage.
The loss of GPS or a lack of integrity in the reported information leads to an unfamiliar situation on the bridge.
The crews of the Pole Star and the Galatea were expecting to lose GPS, were well-trained, and had primed other systems so they could navigate safely. In real life, there would be no advance notice, and the impact on the crew would be more severe.
The impact of low satellite numbers, as predicted in the 2008 GAO report, could produce poor constellation availability and a loss of PNT information for a considerable period of time. This could result in the same outcome as observed in the GPS jamming trials when entering State 3, where many systems on the bridge failed and entered an alarm condition.
Space weather events are difficult to predict both in terms of when they may occur and their severity. Events could affe
ct satellite positions, their operation, and the reception of their signals by the user, and are clearly a threat.
The GLAs strongly support the need for a resilient PNT solution, one that could continue to provide reliable information during such threats for the safety and benefit of all mariners.
Acknowledgment
This article is based on a paper given at the Institute of Navigation’s 2011 International Technical Meeting.
Alan Grant is a principal engineer for the Research and Radionavigation Directorate of the GLAs of the UK and Ireland, technical lead and project manager for all GNSS projects there. He has a Ph.D. from the University of Wales.
Paul Williams is a principal development engineer with the Directorate and currently technical lead of the GLAs’ eLoran Work Programme. He has a Ph.D. in electronic engineering from the University of Wales.
George Shaw is an engineer at the Directorate and holds a master’s degree in mathematics from the University of Cambridge.
Michelle De Voy is a development engineer for the Directorate, with an MSc in oceanography from the University of Southampton and an MSc in satellite positioning from the University of Nottingham.
Nick Ward is research director of the General Lighthouse Authorities of the UK and Ireland, with responsibility for strategy and planning of research and development.
In a few weeks, we will again observe the tragic anniversary of the 9/11 attacks on the United States. This will mark nearly a full decade since that terrible day that changed the lives of people around the world, forever. Many will remember. Many will mourn. Many will work to ensure that such an event never again threatens any nation. That is a good thing.
Few outside the position, navigation, and timing (PNT) community will also recall that the day before the 9/11 attacks, the U.S. government released a landmark document that described the vulnerabilities of services provided by GPS to disruption, whether by attack or inadvertent interference. The Department of Transportation Volpe Center’s GPS vulnerability assessment recommended that services utilizing GPS-provided PNT seek alternative sources of these services. What decisions and actions have the findings and recommendations of this report promoted? The answer is most disturbing.
The U.S. government has sealed the fate of Loran-C and kept the decision on an enhanced Loran system (eLoran) in limbo for more than 10 years. The government has spent hundreds of thousands (if not millions) of dollars studying the problem over and over again and either ignoring or classifying the results. The Department of Homeland Security (DHS), a direct outcome of the 9/11 attacks, has done nothing to address the need for a national backup other than study and re-study the problem and disregard the findings and warnings of world-class PNT experts.
On the positive side, a recent paper from the Federal Aviation Administration (FAA) attempts to address the problem by proposing to investigate alternative PNT (APNT). While the FAA does this under its Title 49 responsibility and authority to ensure the safety, security, and efficiency of our National Airspace System (NAS), and the alternatives it is looking at are certainly aviation-centric, it is admirable that somewhere in this government someone is finally moving forward to define and implement a real, operational PNT alternative to GNSS and its augmentations. [An abridgement of the FAA paper appeared in the July GPS World; the full paper is available here.]
I applaud the FAA’s actions and only hope that bureaucrats and bureaucratic processes don’t penalize it for its efforts.
But the question remains: When will a decision on the U.S. national PNT backup be made? The urgency of this issue can be highlighted by posing some simple questions about another current threat to the U.S. infrastructure and economy.
To what extent are GNSS-provided PNT services being used to identify the amount and movement of the oil in the Gulf of Mexico? What level of information exactness/integrity would be lost if GNSS-provided PNT services were not available?
To what extent are GNSS-provided PNT services being utilized by cleanup crews and other impact-mitigation services? How would the efficiency of the cleanup/mitigation activities be impeded if GNSS-provided services were not available?
Finally, what is the opportunity cost of not having a national PNT backup? Why has this decision been so hard to make? One would intuit that it has encountered political obstacles, not scientific ones. What are they, exactly?
While the FAA is doing what it must to ensure a safe, secure, and efficient national airspace, what about the rest of us? The boaters, the truckers, the farmers, the power transmission people, the telecom providers, the cell-phone users? The list goes on and on.
It has been nine years. Why is this so hard?
As we take time on September 11 to remember where we were when we heard the news, to mourn those lost, and to do, each in our our way, something to ensure that such a thing never happens again, we should also take time on September 10 to thank the folks at the Volpe Center for their important efforts. And we should try, each in our own way, to do something to ensure that the effects of a loss of GNSS-provided services will be once and for all properly mitigated.
The masked engineer harbors strong convictions, matched by a desire to hold onto a day job.
A packed audience attended the National Physical Laboratory in the United Kingdom for a February 23 meeting titled, “GPS Jamming and Interference: A Clear and Present Danger,” organized by the Digital Systems Knowledge Transfer Network.
In his keynote address, David Last described a dark, silent and dangerous world without GPS. He regaled attendees with tales from his experience as a GPS forensic expert, assisting the police who beat a path to his door bearing interesting boxes that turned out to be all sorts of jammers: of GNSS, of mobile phones, and of other radio systems. Last pointed to the near future when he believes that spoofers will undoubtedly make an appearance. The defences are limited: detection, prosecution, and the use of alternative sources of positioning, navigation, and timing information, perhaps eLoran.
His final insight was this: “Navigation is no longer about how to measure where you are accurately. That’s easy. Now it’s how to do so reliably, safely, robustly.”
Jim Doherty, from the U.S. Institute of Defense Analyses, discussed the use of existing resources for time and frequency backup. Drawing on his experience, Doherty delivered three overarching thoughts:
use all available means;
re-use existing systems where possible; and
produce integrated time and navigation.
He advised the audience to be conservative with their designs and not to go too close to the boundary conditions. He also noted that there is an important trade-off between independence and cost when considering complementary systems. Finally, he identified a potential need for eLoran to support synchronisation in aviation’s multi-lateration systems.
Moving on, Alan Grant of the UK General Lighthouse Authorities (GLA) described recent GPS jamming trials. He demonstrated that GPS jamming has wildly different effects, ranging from total denial to hazardously misleading information (HMI). HMI was particularly problematic: it caused the ship’s GPS receivers to report a realistic course and speed well away from the truth that was provided by the GLA’s eLoran system. He noted that the impact depends on the ship’s bridge design.
Professor and consultant Martyn Thomas spoke on an ongoing Royal Academy of Engineering study on GPS vulnerability, which brings together experts from across the UK and will report in early June.
This was followed by three presentations on coverage prediction by Robert Watson of Bath University, on interference detection using the U.S. National Geospatial Intelligence Agency’s GPS Jammer Location (JLOC) system by Alison Brown of NavSys Corporation, and on the GNSS Availability, Accuracy, Reliability anD Integrity Assessment for Timing and Navigation (GAARDIAN) interference detection system by Charles Curry of Chronos Technology.
The conference audience learned that any system can be jammed, that JLOC detects thousands of jammers on a daily basis — nearly all of them unintentional — and that the GAARDIAN system has integrated GPS, eLoran, and clocks for interference detection and mitigation.
Tom Willems from Septentrio and Peter McIlroy from Raytheon gave a good overview of what can be done with receivers and antennas. Willems focused on pulse blanking and adaptive notch filtering. He saw a clear trend towards hybridization, and confirmed that manufacturers recognise that GNSS is not a golden bullet — they can mitigate some interference but not all.
Peter McIlroy told listeners to “defeat interference and jamming before you detect it.” This included hybridization with inertial systems, putting some form of barrier between the antenna and the jammer, and the use of controlled pattern-reception antennas. He suggested that controlled pattern-reception antennas might become available for civil use.
Finally, Paul Groves from the University College London gave a very useful overview on positioning without GNSS. He addressed radio and non-radio systems and presented a fascinating chart that related the various radio systems in terms of range and lifecycle (Figure 1). The message was very timely given the need for complementary systems expressed by all speakers.
FIGURE 1. Range and lifecycles of current radio systems (courtesy Paul Groves).
I then chaired a lively panel discussion with David Last, Martyn Thomas, Charles Curry, Jim Doherty, and Tom Willems. I led off by focusing the discussion on resilient PNT, referring to the UK Center for the Protection of National Infrastructure’s definition for resilience: the equipment and architecture used are inherently reliable, secured against obvious external threats, and capable of withstanding some degree of damage.
The panel agreed on the need for hybrid solutions with multiple technologies. It expressed concerns that cheap GPS receivers are components in many systems, and it is too easy to overlook them. Martyn Thomas brought insight from the computing world and noted that we need to avoid single points of failure and to demonstrate independence.
Do our governments understand and should they do more? The panel thought that different governments are at different points on a journey, and that very few policymakers understand how a loss of GPS impacts critical national infrastructure. It was suggested that the European Union lags behind, due to the focus on Galileo.
This led to an interesting discussion about economics and funding. Martyn Thomas said that GPS vulnerabilities have grown, and that GPS competitors have disappeared for economic reasons, leaving us dependent on GPS. He pointed out that there are limited mechanisms for sharing funding and questioned whether there are many (any) organisations that are prepared to take the risk.
If you have limited funding, should it be used for detection or mitigation? The panel agreed that both were needed, but the prevailing view was that mitigation is more important, and that this needs to be supported by human factors activity.
In Summary. GNSS interference is a real and present danger. It is probably more widespread than generally assumed, and it is here to stay. We can harden our GNSS systems with improved receiver and antenna design, but this will mitigate only some interference, not all. The problem is cost. Cheap — and vulnerable — GNSS receivers will inevitably find their way, unseen, to the heart of our critical infrastructure. We need resilient positioning, navigation, and timing based on independent and complementary systems and sensors. Demonstrating independence is vital but not necessarily straightforward, and true independence costs money. The greatest challenge is helping policymakers understand the risks of relying on vulnerable systems and the need for resilience.
Finally, I return to Jim Doherty’s overarching thoughts: use all available means; re-use existing systems where possible; and produce integrated time and navigation.
eLoran, anyone?
SALLY BASKER is director of research and radionavigation for the General Lighthouse Authorities of the United Kingdom and Ireland.
Since that time the U.S. Coast Guard spent more money dismantling the legacy LORAN-C infrastructure and antennas than it would have taken to complete the 20% upgrade for a full transition to eLORAN. Taking down the Port Clarence, Alaska, tower, the video of which was a YouTube favorite for many weeks, cost an estimated $8 million. The destruction of the towers in Attu (right), Shoal Cove and St. Paul were probably on average $5 million each. With the tower removal in Baudette, Minnesota, the cost of removing Loran towers to date cost close to $25 million. One could argue that the administration created some jobs in these “shovel-ready” tower tear downs, but I have no doubt that a better use of the funding would have been to deliver a robust positioning, navigation, and timing backup for the nation. But alas that is ancient history in the technology world, a whole 18 months to be exact.
In February 2012 the U.S. Coast Guard Research & Development Center (R&DCEN) announced it had entered into a Cooperative Research and Development Agreement (CRADA) with UrsaNav to research, evaluate, and document at least one alternative to the Global Positioning System (GPS) as a means of providing precise time. The alternative under consideration is a wireless technical approach for providing precise time using U.S. government facilities and frequency authorizations.
