Trinity House RFP Would Modify Loran Stations to Backup GPS

Trinity House issued a RFP (request for proposals) in December for an enhanced loran (long range navigation) system, dubbed eLoran, which would serve as a backup to GPS.  Some believe this action could increase pressure on the FAA to do the same.

ELoran enhances loran's accuracy through the use of differential correction systems that are well-established in GPS, along with the ability of receivers to tap into signals from multiple stations.  Loran, itself, provides location information from two low-frequency transmitters, each of which send signals with slightly different times.  Receivers determine their location based on the time difference of the signals received from the two transmitters.

The U.K. has one loran station, and there are seven others in Europe.  The U.S. Loran system covers all coastal waters in the lower 48 states and parts of Alaska.

In a recent white paper prepared by Aviation Management Associates (AMA) for the FAA, the authors, Dr. Robert Lilley, Gary Church and Mike Harrison, advocate the use of eLoran to backup GPS, arguing that in spite of improvements, GPS signals remain vulnerable to both intentional and unintentional disruption.

The AMA paper maintains that both GPS and its complimentary WAAS (wide area augmentation system) have become national and international assets that provide services well beyond aviation and marine harbor entry to include increasingly ubiquitous efficiencies for other essential industries such as surface transportation, telecommunications, and information services, not to mention the multifaceted ways they provide everyday conveniences for millions of people.

If a widespread GPS disruption should occur, the authors believe that even though in-flight aircraft can be recovered, and others can be prevented from flying, without a GPS backup; and while ships can wait off shore; and while the loss of public conveniences and services - including those now attributed to saving lives in emergency situations - might be tolerated for a short period, the overall social and economic damage to a nation, such as the U.S., would quickly become very serious.

For aviation, the debate about a GPS backup is no longer only about just navigation, the paper asserts.  The FAA has made it known that ADS-B (automatic dependent surveillance-broadcast) will become America's primary means of surveillance - and ADS-B relies on satellite navigation to provide an aircraft's precise position report.  Furthermore the U.S. Joint Planning and Development Office (JPDO) has also identified precision performance and four-dimensional (which includes time), trajectory-based separation as the way aircraft will be managed in the Next Generation Air Transportation System (NGATS), which will be highly dependent on GPS for its PNT.

The Case for eLoran

Since 2002 there has been a technical and infrastructure upgrade of loran C's capabilities, transforming it into what is now called eLoran.  Besides improving the performance of loran C, eLoran has a new design called "all-in-view" that treats every loran station transmitter as if it were a GPS satellite "bolted to the ground."  This attribute is an important reason why eLoran has become a viable backup to GPS.

The AMT paper contends that eLoran has changed the technology from a "might do" GPS backup in 2002 to a "can do" backup in 2006, and is the lowest cost technology that provides full PNT backup for GPS, and ultimately Galileo as well.

The General Lighthouse Authorities (GLA) of the U.K. and Ireland, which along with Trinity House manage aides to navigation in the U.K., including loran and DGPS systems, said in its own report on eLoran released May 2006 that they also believe the threat to the Global Navigation Satellite System (GNSS) from terrorism or criminal jamming is "credible, real and likely to have significant economic and financial costs."

According to the GLA report, eLoran can provide an excellent back up to GNSS because it transmits high power signals less susceptible to jamming than GPS or Galileo signals.  (Galileo is an alternative civilian satellite navigation system that is supported by the European Union and several other countries around the world.)

ELoran provides the ideal second input to any e-navigation system by removing vulnerabilities to jamming attack or unintentional interference associated with satellite navigation systems. "In fact, there is no realistic alternative to eLoran in doing this," the GLA report concluded.  01-12-2007.

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