GPS: Global Positioning System. The Geographer’s best friend! You can say with confidence… “I’m not lost!, I’m never lost!”*. *Of course, where everybody else is or how to find your destination…. That’s a different question!.
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*Of course, where everybody else is or how to find your destination…. That’s a different question!
Each Satellite constantly broadcasts the time and every 30 min or so it also broadcasts an ephemeris which is the projected location of all satellites in the constellation.
The satellite broadcasts the time, the receiver compares the time from the satellite to its internal clock… even at the speed of EMR propagation there is a slight delay… this delay provides a distance to each satellite.
Information in these notes is taken from:
GPS Receiver Accuracy by C.J. Hoare,
GlobeStar Positioning Services Inc.
FAA performance test of the GPS and Glonass (Russian) systems:
Individual receivers vary in the amount of ‘noise’ they produce … noise produces error in the internal clock.Again… a nanosecond (A nanosecond (ns or nsec) is one billionth (10-9) of a second ) = .3 meters of error
The configuration of the satellite constellation can result in either a strong or a weak position solution. This is called DOP, Dilution of Precision