Where do you want to GPS today?

Dan Tebbutt

In the latest James Bond saga, a stooge of villainous media mogul Elliot Carver hacks into Global Positioning System (GPS) navigation satellites in order to send a British warship off course and provoke conflict with China. 007 eventually saves the day through clever keyboard karate and his usual Q-tech gadgets, but the essential question remains: just how secure is the GPS network?

The issue is becoming more pointed as GPS finds wider acceptance for everyday consumer and commercial purposes. Last October, for example, BMW launched a GPS-powered navigation system to help drivers find their way around Melbourne. An on-board computer correlates GPS tracking data with street directory information and physical landmarks to guide luxury car owners through city streets with voice prompts and a high-resolution display. Service coverage extended along the Hume Highway to Canberra and Sydney last month, and the Gold Coast-Brisbane-Sunshine Coast corridor is scheduled to come online mid-year. Lexus and Toyota are promising satellite navigation for their prestige cars, and Holden is currently assessing GPS products such as OnStar (www.onstar.com) for potential deployment in more affordable vehicles.

Handheld computers can access the GPS system for purposes as diverse as finding a restaurant, finding a bushwalking trail or finding minerals. TeleType GPS (www.teletype.com/gps/) accessories work with Apple's Newton, Windows CE palmtops and Windows 95 laptops. GPS interfaces are also available for 3Com's Palm Pilot (www.llamas.org/gps/).

Commercial GPS users include taxis, railways, fishing boats, security firms, crop-treatment aircraft -- almost any business where fleet management matters. GPS can calculate location to within 100 metres anywhere in the world using a constellation of 24 satellites circling 20,000km overhead. For users that require greater accuracy, a supplementary system called Differential GPS (DGPS) can narrow down position to less than five metres. DGPS works through an overlay network that augments GPS data by measuring position relative to fixed ground stations whose exact location is known. Off-shore and outback propecting relies heavily on DGPS services from companies such as Racal and Dutch engineering conglomerate Fugro. Privatised former government agency Ausnav is forging an even broader DGPS customer base by transmitting its positioning signals alongside the Triple J radio broadcast throughout Australia.

Aviation is another obvious industry with enormous use for fine-grained GPS data. Australia recognised GPS as the primary en route navigation mechanism in December 1995, and even the smallest planes now carry GPS navigation utilities. During landing GPS is officially only a supplementary aid, but most airports have GPS installed and a number of smaller airports such as Wollongong and Goulburn have improved landing procedures through GPS guidance systems.

Air Services Australia's navigation expert Keith McPherson said Australia is at the forefront of research into DGPS-driven landing systems. Melbourne airport recently tested DGPS successfully, and Canberra will soon experiment with a competitive product to ensure choice. McPherson is leading a local research endeavour to develop a wide-area DGPS grid for aviation and other industries, and he's upbeat about the potential for exportable products down the track. "We've proven the concept, now we want to join forces with industry and sell it," McPherson said.

If GPS is to help land passenger planes and pilot oil tankers into port, security is a paramount concern. Since the network is operated by the US military, a reasonable level of protection is expected. But what about less controllable threats like weather conditions, atmospheric interference, radio-wave obstruction or equipment failure? And what happens to civilian GPS users when a military crisis interrupts the positioning service?

Dr Elizabeth Essex, a physicist at LaTrobe University, believes GPS could be susceptible to interference from tumult in the Earth's atmosphere. She fears magnetic disturbances in the ionosphere and upper layers could delay or, in extreme cases, dangerously distort GPS tracking signals. What's more, the situation is going to become worse over the next five years, according to Essex, because we're heading into a cyclical upturn in sunspot activity that could send ionisation levels sky-high. "This could lead to a complete loss of signal," Essex told LaTrobe's research journal.

McPherson says the extent of the sunspot problem is unclear, but DGPS ground-stations should be able to correct anomalies by comparing measured GPS positions against known DGPS status. However, Richard Harris from the Australian Maritime Safety Authority (AMSA) claims the GPS L-band frequency (1.2GHz and 1.6GHz) is not overly affected by atmospheric moisture, so GPS is relatively impervious to storms and rain. He said extreme ambient noise like lightning can drown out the low-frequency broadcast for marine DGPS.

Atmospheric threats could hamper consumer users, but Associate Professor Chris Rizos from the University of NSW's School of Geomatic Engineering maintains only the most exacting specialist users will notice the loss of accuracy. "Still the biggest error is the man-made Selective Availability limitation," Rizos said, referring to the US defence policy that artificially limits GPS to 100m granularity. GPS readings could go as far as 15-30 metres without this Selective Availability constraint. However, the US has promised to reconsider this policy after 2000 and Rizos is confident it may be "eliminated" within three years.

Greater accuracy is sometimes available now, according to John Manning, a GPS expert with the Australian Surveying and Land Information Group (AUSLIG). But noone should depend on GPS alone for minute positioning because the service's precision could be deliberately reduced during a military crisis. "Under its service terms, the US can degrade to 100m readings during a hostile situation so the enemy cannot use GPS against them," explained Manning. "Enemies could only get 100m accuracy, and the same for consumer users."

Manning says accurate GPS readings can be obtained everywhere from the Antarctic to the blazing central deserts, helping Australian pioneers overcome "the tyranny of position".

"From the time of Burke and Wills to current soil, vegetation and mineral exploration, Australian explorers spent most of their time trying to figure out where they were," said Manning. "Now they can press a button for an instant position on their computer."

AUSLIG is using GPS to recalculate with new exactness the position of all trig stations used by surveyors to map land. Most old coordinates require a correction of 190-205 metres. State and Territory Governments will gradually enter refreshed data into land management systems like ecology and land titles records -- although Manning emphasises that physical positions will not change. Trig stations will stay put and property boundaries will be unaffected.

So how realistic is the Tomorrow Never Dies scenario about hackers compromising GPS readings? Rizos says the notion is "far-fetched" because six satellites should be visible at any one time and rogue signals would be picked up. Still, aviators who depend on accurate positioning as a matter of life or death want DGPS signals to include warnings about when satellite data is not reliable, be it from atmospheric or human interference.

Confirmed reports in the US about Inmarsat voice calls obstructing GPS signals leave experts worried that the GPS radio band is not sufficiently buffered. A proposal at last year's World Radio Conference to allocate adjacent bandwidth to other satellites was put on hold for two years. However, McPherson anticipates continued protection for the GPS band.

Jamming GPS signals from close range is relatively easy, Rizos claims, but the more likely scenario is inadvertent interference from radio hobbyists. McPherson says jamming is occasionally reported to Air Services, although it's "insufficient to cause any alarm to date". The organisation recently tested the vulnerability of commercial GPS receivers at Woomera range. Results are not yet processed, but McPherson attributes most problems to poor aerial installation. AMSA's Harris believes the next generation of GPS will address the jamming threat, although risks are presently low. "The danger is the same as the chances of any intentional harm," he said.

GLONASS: The other GPS

GPS is a big money spinner for the US economy, even though there are no access fees to receive the signal. The satellites were originally launched for defence during the Star Wars era. Later the US Government decided, in an act of international philanthropy, that civilians would have free access to GPS. This largesse was predicated on the belief that US manufacturers would dominate the market for professional GPS equipment.

To date that faith has been repaid. That's left many Europeans uneasy about the US monopoly on both infrastructure and industry. A number of German and British companies are lobbying the European Union to finance the Russian GPS program in order to foster European technology industries. However, Russia has rejected offers where assistance was conditional on surrendering control of the program.

The biggest problem confronting GLONASS (Global Navigation Satellite System), the Russian positioning system, is its dubious reliability. GLONASS birds keep falling out of the sky and Russia's impoverished defence department does not have enough money to launch new ones. Briefly in 1996 a complete 24 satellite constellation was in place, but the count is now down to 14, according to the GLONASS monitoring program at Massachusetts Institute of Technology (vega.atc.ll.mit.edu). Launches scheduled for earlier this year were delayed.

Problems with GLONASS are lamentable, John Manning says, because many users would value a second network. In fact, despite question marks over its technology, GLONASS can provide greater accuracy (down to 30m) because Russia does not impose artificial Selective Availability limitations. Aviators would like access to both systems as a backup, while Manning says mapping and mineral surveys can combine GPS and GLONASS for superior accuracy. Using both systems brings up to 15 satellites into view -- and gaps in GLONASS coverage are less of a problem for surveyors whose top priority is precision.

-- Dan Tebbutt

NOTE: This version is as submitted and differs slightly from the published text. The edited version as it appeared in The Australian is not online.

This article was published in The Australian, 12 May 1998, page N.
Full text © copyright Dan Tebbutt.
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