What is the global positioning system and how does global positioning system allow scientists to measure the rate of motion of tectonic plates?

Answer 1

The global positioning system is a navigational aid maintained by the US Air Force. It is composed of three segments: ground control stations, 24 active satellites with 6 idle spare satellites, and receivers. Each satellite contains an atomic clock and transmits time signals and coded identification and status. The ground control stations monitor the satellite status and transmit corrections as well as controlling which of the 30 satellites in orbit are active and which are spare. Receivers pick up the signals from the satellites, use the time signals to calculate distances to each satellite they detect and using a method of triangulation compute position and velocity of the receiver. Most receivers also contain a navigational map database that they use to display something useful to a human operator to help him know where he is.

However to measure the rate of motion of tectonic plates the navigational database is not needed. Instead receivers mounted at known locations on the plate contain nonvolatile data storage in which they record the position and velocity that they computed from the satellite signals. This data can later be read out and used to prepare maps showing the movements.