|Global Positioning System |
A system of satellites combined with receivers on the Earth that determines the latitude and longitude of any particular receiver through triangulation. The distance of the receiver to three of the satellites is ascertained by measuring the time-delay of a predetermined radio signal (called a pseudo-random code). Errors in timing can be corrected by checking the signals against the signal from a fourth satellite. Current systems can pinpoint the location of the receiver with an accuracy of around 5 m (16 ft). The system is used for navigation, surveying, and many other applications. Compare loran.
A U.S. military satellite system now available for public use that allows those with a GPS receiver to locate their position on the surface of the Earth to within a few feet. A constellation of twenty-four satellites orbits the Earth, each of which transmits a radio signal giving both location of the satellite and the time of the transmission. Triangulation of three separate signals is then used by the receiver to determine its position on the Earth's surface.