GPS

GPS stands for Global Positioning System. Users of a global positioning system can calculate their location anywhere on the earth. There are currently two "public" GPS systems. The NAVSTAR system which is owned by the United States and is managed by the Department of Defense and the GLONASS system which is owned by the Russian Federation. Global Positioning Systems are space-based radio positioning systems that provide 24 hour three-dimensional position, velocity and time information to suitably equipped users anywhere on the surface of the Earth. The GPS signals do not penetrate through water so subsea vehicles must surface to get a GPS fix. The system works by a constellation of satellites that transmit timing information, satellite location information and satellite health information. The user requires a special radio receiver - a GPS receiver - to receive the transmissions from the satellites. The GPS receiver contains a specialized computer that makes calculations based on the satellite signals. The user gets 24 hour, three-dimensional position, velocity and time information and does not have to transmit anything to the satellite

Standard GPS has accuracy on the order of 10 meters. Differential GPS uses a correction signal from a regional source and has typical accuracies of 2-3 meters. Real-Time Kinematic (RTK) GPS is a technique that uses a local base station that is surveyed in and which transmits a local correction signal to a roving receiver. RTK can yield positional accuracies of up to 10 centimeters.

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