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Intoduction

Selective Availability (SA) was the intentional degradation of the Global Positioning System (GPS) satellite signals by the United States. When SA was turned off during early May of 2000, position accuracy for civilian GPS receivers used without correction increased from +/- 100 meters to less than +/- 10 meters (figure 1). Civilian users of GPS are now able to pinpoint locations up to 10 times more accurately than in the past.


The decision to discontinue SA is the latest measure in an ongoing effort to make GPS more useful for civilian and commercial users worldwide. In addition, two new civilian signals will be added to enhance the civilian and commercial service. The Missoula Technology and Development Center tested commercially available GPS receivers and compared them to the military receivers now widely used by the Forest Service. This report describes the initial results of those tests conducted during the summer of 2000.
Graph that showed the change in position error when selective availability was turned off.
Figure 1-The change in position error when selective availability was turned off.

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USDA Forest Service - Missoula Technology & Development
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