|
GPS was developed by the United States Department of Defense.
The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites GPS was originally intended for military applications, but in the 1980s, the government made the system available for civilian use.
GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.
In addition to person-to-person communication however, satellite technology and the Internet are also allowing us to quite literally keep our eyes on the farthest reaches of the globe, 24 hours a day.
How GPS works
Global Positioning System satellites transmit signals to equipment on the ground. GPS receivers passively receive satellite signals; they do not transmit.
GPS receivers require an unobstructed view of the sky, so they are used only outdoors and they often do not perform well within forested areas or near tall buildings.
GPS operations depend on a very accurate time reference, which is provided by atomic clocks at the U.S. Naval Observatory. Each GPS satellite has atomic clocks on board.
Each GPS satellite transmits data that indicates its location and the current time.
All GPS satellites synchronize operations so that these repeating signals are transmitted at the same instant.
The signals, moving at the speed of light, arrive at a GPS receiver at slightly different times because some satellites are farther away than others.
The distance to the GPS satellites can be determined by estimating the amount of time it takes for their signals to reach the receiver. When the receiver estimates the distance to at least four GPS satellites, it can calculate its position in three dimensions.
Differential GPS
Differential Global Positioning System (DGPS) is an enhancement to Global Positioning System that uses a network of fixed, ground-based reference stations to broadcast the difference between the positions indicated by the satellite systems and the known fixed positions.
|