GPS Geodesy

Overview of Global Satellite Positioning (GPS)

Global Positioning System (GPS) is a space-based technique for studying geodesy. GPS has been
the most useful for assessing crustal movements of the Earth. By taking precise, repeated
measurements, geologists can assess active movement along faults or between plates.

Currently, 24 satellites are in orbit 20,000 km above the Earth as part of the NavStar system of the U.S. Department of Defense. These satellites continuously transmit radio signals back to Earth which are interpreted by ground receivers. GPS ground receivers are located at carefully chosen points on the Earth's surface and separated by hundreds to thousands of kilometers. These receivers can determine their precise position on Earth including longitude, latitude, and elevation. To record position, the receiver must simultaneously receive signals from at least four satellites. Changes in position record tectonic motions of the plates.

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