Civilians get better GPS

For users of the Global Positioning System (GPS), getting lost just became harder. On Monday, President Clinton directed the Defense Department to stop degrading signals from 24 Air Force GPS satellites. The move improves the navigational precision available to civilian GPS users by about 10-fold, putting it on a par with that of the military. Civilians already use 4 million GPS receivers, which may be handheld or installed in cars, boats, or planes.

With GPS signals available Monday, civilians could identify this Colorado site only to a spot with a 60.7-yard radius (above). By Tuesday, the same GPS device could pinpoint it to within a 7.9-yard radius (below). NGS/NOAA

NGS/NOAA

Children calculate lightning’s distance by counting the seconds from a flash to the rumble of thunder. A GPS device works similarly, notes Dennis G. Milbert of the National Geodetic Survey in Silver Spring, Md. It triangulates its position, he explains, by comparing its internal clock with time and position signals from at least 4 of the 24 atomic clocks on GPS satellites.

Janet Raloff

Janet Raloff is the editor of Science News for Students, a daily online magazine for middle school students. She started at Science News in 1977 as the environment and policy writer.

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