Global Positioning System

Applications

The primary military purpose is to allow improved command and control of forces through an enhanced ability to accurately specify target locations for cruise missiles or troops. The satellites also carry nuclear detonation detectors, which form a major portion of the United States Nuclear Detonation Detection System.

The system is used by countless civilians as well, who can use the GPS's Standard Positioning Service worldwide free of charge. Low cost GPS receivers (price $100 to $200) are widely available. The system is used as a navigation aid in aeroplanes, ships and cars. The system can be used by computer controlled harvesters, mine trucks and other vehicles. Hand held devices are used by mountain climbers and hikers. Glider pilots use the logged signal to verify their arrival at turnpoints in competitions.

On May 1, 2000, US President Bill Clinton announced that this "Selective Availability" would be turned off. However, for military purposes, "Selective Deniability" may still be used to, in effect, jam civilian GPS units in a war zone or global alert while still allowing military units to have full functionality. European concern about this and commercial issues has resulted in the planned GALILEO positioning system. Russia already operates an independent system called GLONASS (global navigation system), although with only 12 active satellites as of 2004 the system is of limited usefulness.

Military (and selected civilian) users still enjoy some technical advantages which can give quicker satellite lock and increased accuracy. The increased accuracy comes mostly from being able to use both the L1 and L2 frequencies and thus better compensate for the varying signal delay in the ionosphere (see above). Commercial GPS receivers are also required to have limits on the velocities and altitudes at which they will report fix coordinates; this is to prevent them from being used to create improvised cruise or ballistic missiles.

Many synchronization systems use GPS as a source of accurate time, hence one of the commonest applications of this use is that of GPS as a reference clock for time code generators or Network Time Protocol (NTP) clocks. For instance, when deploying sensors (for seismology or other monitoring application), GPS may be used to provide each recording apparatus with some precise time source, so that the time of events may be recorded accurately.

Back to GPS overview.

From Wikipedia, the free encyclopedia.