The U.S. Global Positioning System (GPS) satellites provide data that are used in a broad spectrum of Earth science disciplines, including geodesy and geodynamics. Currently, there are 24 satellites, each travelling in a 12-hour, circular orbit 20,200 kilometers above Earth. The satellites are positioned so that at least six are nearly always observable from any point on Earth. The GPS satellites transmit ranging codes on two-radio frequency carriers at L-band frequencies, which can be detected by ground-based GPS receivers. Special ground-based stations perform satellite monitoring that permits the locations of GPS receivers to be determined with a high degree of accuracy. UTIG has several projects which use GPS technology.

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