GIS6

Global Positioning System GPS
• GPS is a constellation of ~30 satellites in a Medium Earth Orbit at 20,200 km height. Satellites are arranged in six different planes.
• Coverage is available worldwide, Each satellite has a speed of 3.9 km/s and a circulation time around Earth of ~12 h.
• GPS was created by US Department of Defense from 1978 to 1993 (complete).
– Actual name is NAVSTAR (Navigation System for Timing and Ranging).
• Initially, high accuracy only for US military applications, Currently, there is dual military and civilian use.
GPS consists of three basic components:
1- Control segment: Related to system operation by the US military Supported by   monitoring stations.
2-  Space segment:  Consists of the orbiting satellites with precise atomic clocks.
3-  User segment: Consists of receivers used for positioning on Earth surface.
How does GPS actually work?
• Each satellite sends signals with orbital position and accurate time, GPS receivers computes time difference to each satellite. Compares time when signal was sent with the time the signal was received.
• Position on Earth can be estimated with at least three satellites.