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The Global Positioning System (GPS)

 

Selective Availability (SA)

The Global Positioning System provides a way for people and equipment to determine a location anywhere on Earth but at the controlled accuracy of the United States government.

Selective Availability (SA) is the factor that greatly influences the GPS receiver's ability to determine it's position. The United States government intentionally degrades the GPS satellite's signal for civilian GPS receivers. The government introduces small errors into the signals that makes the GPS receiver less accurate. These errors are referred to as " selective availability", or SA.

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This information can change without further notice and availability. Contact the U.S . government for up-to-date details on GPS availability.

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GPS NEWS

Santa Clara, Calif. -- May 2, 2000

SA Turned Off - Increasing GPS Accuracy

President Clinton announced the U.S. government’s removal of Selective Availability (SA), which degrades GPS signals. As President Clinton noted in his announcement, the result of removing SA will be about ten times greater accuracy for public users of GPS.

With millions of hand-held GPS products in the hands of consumers, the impact of ending Selective Availability of GPS signals is significant.

Our product offerings have become more valuable and useful overnight. The same GPS receiver that provided accuracy within 100 meters of a user’s location yesterday, is providing position fixes with as good as 10-meter accuracy today. This change immediately makes GPS more accurate and reliable, and thus more valuable to our customers.

The significant increase in accuracy is very good for everyone involved in GPS. Precision-minded DGPS users who rely on transmissions of correction data, such as those broadcasted by the U.S. Coast Guard’s reference stations, would normally need correction signals every three to five seconds to obtain a high level of accuracy. Now, the same users will need significantly fewer transfers of data to maintain the same level of accuracy.