Pentagon is probably jamming
GPS in Afghanistan, experts say
BY BOB BREWIN, COMPUTERWORLD
October 26, 2001
The U.S. Defense Department
has probably been selectively jamming signals from the Globe Positioning
System (GPS) in Afghanistan since the start of the air campaign earlier
this month, according to non military GPS experts.
The experts emphasized that
the jamming in Afghanistan will have no effect on civilian users, including
airlines, which increasingly rely on GPS for transoceanic navigation.
Signals from the GPS satellite system available to civilian users provide
an accuracy of 36 meters or better, while separate, encrypted military
signals used to guide so called smart bombs in Afghanistan provide accuracy
within 6 meters, according to Richard Langley, a professor of geodesy
and precision navigation at the University of New Brunswick.
Langley said the Pentagon has
developed the capability to jam civilian GPS signals with a specific targeted
area and could easily deny the 36-meter-accuracy civilian signal to the
Taliban forces without interfering with users in other areas of the world.
Depending on whether the pentagon, which developed the operates the 28-satellite
GPS constellation, uses airborne or ground jammers, this could deny the
signal to the Taliban over a wide area, with some of the jamming potentially
spilling over into Pakistan.
GPS receivers, which sell for
as little as $100 for a simple version used by hikers, plot position through
sophisticated triangulation operations which with at least three GPS satellites.
Area jamming would prevent GPS receivers used by the Taliban from locking
on to the satellites and deriving a highly accurate location. The Pentagon
has developed this jamming capability to ensure that enemies dont use
the GPS signal to guide their own smart missiles or bombs in an attack
on U.S. Forces.
Sam Wormley, a researcher at
Iowa State University in Ames and manager of an authoritative GPS resources
and accuracy web site, said that the Pentagon definitely has the capability
to jam civilian GPS signals in a given area without interfering with more
precise military signals. Wormley said thats because the military signals
occupy a different and smaller slice of the GPS frequency band that used
by the civilian signals.
The Pentagon doesnt discuss
its GPS jamming capabilities, especially in time of war, but information
readily available on the Web provides an inside into the power of the
GPS jammers in its inventory.
массажный салон . курсы английского языка . ip телефония The Naval Air Warfare Center
Weapons Division in China Lake, Calif., operates electronic test ranges
that have GPS jammers capable of 500 watts of output, according to a Notice
to Airmen (NOTAM) published by the Coast Guard Navigation Center in Alexandria,
VA. The notice warned of unreliable GPS signals within 300 nautical
miles of the test range from Oct. 22 through Nov. The U.S. Department
of Transportation, which includes the U.S. Coast Guard, jointly manages
civilian GPS signals with the Defense Department. Langley said that such
a NOTAM indicates that China Lake is conducting jamming tests and shows
that the U.S. military possesses the capability to jam GPS signals anywhere
it wants.
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