Pentagon Denies GPS to Taliban.


Mar 11, 2001
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Pentagon Denies GPS to Taliban.

By Declan McCullagh, Wired News

2:00 a.m. Oct. 20, 2001 PDT  
WASHINGTON -- The Pentagon said on Friday that it won't limit the accuracy of positioning information that's beamed to civilian global positioning system (GPS) receivers.

In fact, the military says in its new standard that it's boosting civilian GPS quality. The government claims it "now provides civil users a horizontal positioning accuracy of 36 meters, compared to 100-meter accuracy" in the 1995 standard.

But as the military campaign against Afghanistan enters its third week, the Defense Department could take steps to limit the usefulness of GPS receivers in the hands of Taliban forces. GPS units receive signals from orbiting satellites and compute their location and what time it is.

"We have demonstrated the ability to selectively deny GPS signals on a regional basis, particularly ... when our national security is threatened," said Lt. Jeremy Eggers, a spokesman at Schriever Air Force Base in Colorado. That's home to the 50th Space Wing, which oversees GPS.

That would mean only military GPS receivers -- in planes, ships and in the hands of U.S. special forces -- would work within the targeted area.

Eggers wouldn't say if a selective denial would be precise enough to hit just Afghanistan, or if neighboring nations like Pakistan and Uzbekistan would be affected too. He'd only say that the "region can be very well defined."

Selective availability (SA), which globally degraded the quality of GPS available to civilians, has been turned off since a May 2000 executive order signed by President Clinton. It's been replaced by selective deniability, which allows the military to geographically pinpoint areas should it choose to degrade GPS quality.

Pete Brumbaugh, a spokesman for Garmin, a leading manufacturer of civilian GPS devices, said he believed the signal in Afghanistan has already been degraded.

"There is probably a significant dithering of the signal over Afghanistan and other areas where there are military operations," Brumbaugh said. But he's found no effects in North America: "We have been monitoring the situation closely to see if there's any fluctuation in the signal and we haven't found any. It shouldn't have any repercussions on areas that aren't affected by the military operations around the world."

Even if the United States would change its mind and globally limit the quality of GPS signals, GPS experts say it would have little effect on commercial airliners that use the technology in their navigation systems.

Nancy Glass, a spokeswoman for Rockwell Collins, which sells commercial air navigation systems, said: "There would be no consequence if SA was turned on. The separations that are required between aircraft are higher than the difference between SA on and SA off. SA is only 100 meters. The required separation between aircraft is much higher than that -- it's miles."

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