The Dark Side of GPS Page 2

Electronics - April 2002 - GPS Part 2
Electronics — By Ben Ellison — April 2002

The Dark Side of GPS
Part 2: The Larger Truth

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• Part 1: GPS
• Part 2: GPS
• Currents

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The larger truth, the one we missed, was how deeply dependent our whole infrastructure was becoming on a GPS technology that was inherently vulnerable to what are known as "unintentional" and "intentional" problems. It’s all spelled out in this year’s Volpe Report, but had we been listening back in 1999, we might have heard a well-informed skeptic like Bond say, "If we rely on GPS alone, there is the risk, indeed the likelihood, of multiple aviation and marine catastrophes."

The problem is the extraordinary weakness of the GPS signal. It’s a marvel that our little handhelds work as well as they do with data coming in at one ten-quadrillionth of a watt, equivalent to light from a 20-watt bulb 11,000 miles away. Interference from unexpected natural and man-made sources is easy. There is already regular "ionosopheric interference" near the poles; an extended period of solar flares could cause GPS malfunction in well-traveled areas. Satellite navigation is said to be difficult in Italy because certain TV channels are leaking spurious emissions. Recently, automated wireless toll-taking devices installed on bridges have been discovered knocking out local GPS reception.

These sorts of problems will probably be solved with the next generation of GPS, which will add new frequencies and possibly more power to the present signal. However, the issue of "intentional" interference looks much harder, if not impossible, to solve. Bond says, "Anyone with $50 and a soldering iron can make a jammer able to destroy the GPS signal for a hundred miles." The Volpe researchers, who clearly had access to at least some portion of our military’s "dark" GPS technology, detail what a more sophisticated enemy could accomplish. This includes not just widespread and prolonged jamming, but also "spoofing" in which GPS misinformation blankets the real signals.

You can easily imagine the terrible consequences of fake navigation data in foggy harbors and airports. In the aviation world it’s acronymed HMI for "hazardously misleading information" and understood to be much more dangerous than no information at all. But did you realize that many of our telecommunications and power-grid systems are also dependent on GPS for atomic-clock timing capabilities?

The whole scary story is laid out in the Volpe report (available at and was apparently taken quite seriously by our secretary of transportation Norman Minetta. He released it to the public last September 10, and of course the horrid events of the following day could not have done more to emphasize the presence of malevolent and clever forces in our world. The notion of "sole source" electronic navigation has been officially retired for at least the near future. The military, which knows more about GPS vulnerability than anyone, already equips all its GPS-guided vehicles and weapons with alternate electronic backup; the civilian sector, led by Minetta’s DOT, will soon follow.

Much to my surprise, Loran appears to be a prime backup candidate. I remember the complexity of compensating for "Additional Secondary Factors" in coastal waters and switching "chains" on long voyages, and then having the darn signals fade away just short of Bermuda. No wonder the only currently manufactured marine Loran I could find is Furuno’s solid but pricey LC-90 (and the salesman assured me that I really didn’t need it because GPS "never goes out").

Well, it turns out that Loran has been quietly improving. When the DOT decided in the late ‘90s that shutting down the transmitters was perhaps imprudent, it also began to slowly replace old vacuum-tube units with more capable Megapulse solid-state devices complete with cesium clocks. In October 2001 Megapulse received a $40-million contract to complete this process ASAP. Meanwhile, small industrial manufacturers have developed "all in view" Loran receivers that can work with multiple signal chains. Pretty soon we should see more accurate and easier to use Loran sets that will work very well, at least around North America and Europe.

In our age, the ultimate beauty of Loran is how different it is from GPS. With its high power, low frequency, and land-based signals, Loran is much harder to jam or spoof. Thus Bond and his ilk predict the proliferation of integrated GPS/Loran units that can feed our digital charts, radar overlays, etc. with a new level of electronic integrity. I look forward to this development, but I have to admit that my research tends to support the gizmo-leery, belt-and-suspenders approach to navigation that Richard Thiel advocated in his column. In short, the boss was right.

Ben Ellison has been a delivery captain and navigation instructor for nearly 30 years and was recently the editor of Reed’s Nautical Almanacs.

Next page > Currents > Page 1, 2, 3

This article originally appeared in the January 2003 issue of Power & Motoryacht magazine.

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