The average GPS user didn’t always have 15-meter accuracy. In the 1970s, studies showed that the less-accurate C/A-code for nonmilitary use, was more accurate than the U.S. government intended. Originally thought to provide accuracy within 100 meters, experiments showed that C/A accuracy was in the range of 20–30 meters. To reduce the accuracy of C/A-code, the U.S. government developed Selective Availability (SA). SA adds errors to NAVSTAR satellite data and prevents consumer GPS receivers from providing an extremely precise location fix.
Selective Availability was temporarily turned off in 1990 during the Persian Gulf War. There weren’t enough U.S. and allies military P-code GPS receivers, so the Coalition troops used civilian GPS receivers. The Gulf War was the first use of GPS in large-scale combat operations. On May 2, 2000, SA was turned off permanently. Overnight, the accuracy of civilian GPS users went from 100 meters to 15 meters. Turning off SA on a global scale was directly related to the U.S. military’s ability to degrade the C/A-code on a regional basis. For example, during the invasion of Afghanistan, the American military jammed GPS signals in Afghanistan to prevent the Taliban from using consumer receivers in operations against American forces.
Selective Availability was temporarily turned off in 1990 during the Persian Gulf War. There weren’t enough U.S. and allies military P-code GPS receivers, so the Coalition troops used civilian GPS receivers. The Gulf War was the first use of GPS in large-scale combat operations. On May 2, 2000, SA was turned off permanently. Overnight, the accuracy of civilian GPS users went from 100 meters to 15 meters. Turning off SA on a global scale was directly related to the U.S. military’s ability to degrade the C/A-code on a regional basis. For example, during the invasion of Afghanistan, the American military jammed GPS signals in Afghanistan to prevent the Taliban from using consumer receivers in operations against American forces.
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