Global Positioning Systems work by having a hand held reciever which reicieves signals from the 24 satellites put up by the USAF (United States Air Force). The hand held reciever is not capable of transmitting signals.
Usually, GPS does not work well in forests or in the city as trees and buildings, respectively, obstruct the reception of signals. The signal travels at the speed of light, being 3 x 10^8 m/s. Due to that remarkable speed, GPS is usually accurate enough to the meter. That in itself is a remarkable achievement for mankind. With that speed comes teh important need of accuracy from time, and each GPS satellite has an atomic clock on board. This time reference is provided by atomic clocks at the U.S. Naval Observatory.
All GPS Satellites must have a synchronized time, so their repeating signals are transmitted at the same instance. When four or more of these signals are recived by a reciever, it is able to deduce a position in three dimensions. As some satellites are farther from a cingular point, their signals would take a longer time to converge upon that point. Therefore the estimation of time is also used to deduce one's position. From the satellite transmissions a GPS reciever automatically knows the location of the aforementioned satellite. By estimating the distance, the reciever is able to create imaginary spheres, and when four of these intersect, it knows the position. |
