GPS Use Expanding

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It all started in 1973, when a small group of military officers and civilians met in the Pentagon and created a plan for a new navigation system that would use radio-ranging measurements from a constellation of satellites. “It” was the beginning of the NAVSTAR Global Positioning System, a program that has revolutionized the way the U.S. military operates.

More than the military have benefited from the $19 billion system the Air Force has invested in. Civilian use of GPS is increasing, according to Space and Missile Systems Center officials here. Case in point: the Federal Aviation Administration’s proposed Wide Area Augmentation System.

Currently, GPS satellites send out signals with small errors intentionally put in. Commercial receivers, using this corrupted signal, have an accuracy of about 100 meters. Military users can decrypt these signals to increase accuracy to about 16 meters. However, the FAA has plans to make the GPS signal more accurate than even the military’s, and to make it available nationwide through WAAS.

The FAA’s WAAS is based on the concept known as differential GPS. The idea is that if you plant a GPS receiver in a highly surveyed spot, you can compare the known spot with the signal received, and thus figure out the errors. You then transmit the corrections by radio to the receivers out in the field, and you’ve got a “perfect” signal.

Results of a differential GPS system are currently being tested by the FAA at an airport in Atlantic City, N.J. If the FAA likes the results, it plans on broadcasting the corrections nationwide through a network of stations all over the United States.

Col. Mike Wiedemer, director of the NAVSTAR GPS Joint Program Office at the center, said that one of the biggest upcoming challenges concerning GPS is creating a dual-use strategy that allows rapid growth of GPS technology in the civilian sector while securing the military advantages of the GPS system.

“We know that the FAA WAAS system could provide tremendous accuracy improvements on a worldwide basis, down to submeter accuracy perhaps,” Wiedemer said. “However, that accuracy could be offensively or defensively exploited by military adversaries. The question is, how do you balance these two differing uses of the GPS system?”

There needs to be some way of selectively preventing unauthorized, unintended use of high-accuracy navigation signals, Wiedemer said. According to the colonel, there are about 80 potential military applications of the GPS system, very few of which are available to adversaries because of the selective degradation of the civilian signal.

“There are proponents of not allowing the FAA WAAS system to be developed and implemented. There are proponents of letting a completely unconstrained development of the WAAS system proceed,” Wiedemer said. “I believe the answer has to lie somewhere in between.”

A report released May 31 by a panel assembled by the National Academy of Public Administration and the National Academy of Sciences recommended that the military stop putting the errors in the signals since more and more ways of correcting the errors are emerging.

Currently, the Coast Guard uses a differential GPS system to broadcast corrections to help boaters during bad weather, and in some cities GPS corrections are broadcast from local FM stations for a fee.

Paul Kaminski, undersecretary of defense for acquisition and technology, said that the president can declare a national emergency and either greatly increase the error in the signal or turn the signal completely off.

Wiedemer said that this worries many civilian users, who fear shutting off the signal has the possibility for disaster if groups such as the commercial airline industry become too reliant on GPS.

“There’s an enormous battle between supporters of both sides of this issue,” Wiedemer said. “There is no clear cut and easy answer. Both DOD and DOT (Department of Transportation) will need to further study this issue and try to find a solution that works for everyone.” (Highley is assigned to Space and Missile Systems Center public affairs).

Dateline: June 28, 1995
by 2nd Lt. Sam Highley
Air Force News


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