INTRODUCTION:
I. What is GPS:
The Global Positioning System (GPS) is a satellite-based radio navigation system initially developed and operated by the U.S. Department of Defense. In 1996, a law, transferred ownership of GPS from DOD to an Interagency GPS Executive Board to assure that GPS meets civil and military user requirements.
It is a form of satellite communication that allows users to determine their three dimensional position, velocity, and time anywhere on or above the Earth to within about 300 feet, 24 hours a day, in all weather, anywhere in the world with a precision and accuracy far better than other radio navigation systems available today or in the foreseeable future.
Users determine their position by measuring their distance from the group of satellites in space. The satellites act as precise reference points. Even greater accuracy, usually within less than three feet, can be obtained with corrections calculated by a GPS receiver at a known fixed location.
II Components of GPS:
Global Positioning
System consists of three segments:
1) The Space Segment - satellites orbiting the earth
2) The User Segment - the GPS signal receivers owned by individuals.
3) The Control Segment - the control and monitoring stations
Space Segment: The Space Segment consists of 24 operational satellites in six 12-hour orbits 20,200 km (10,900 ml) above the earth at an inclination angle of 55 degrees. The satellites are spaced in such an orbit so that at any time a minimum of 4 satellites will be in view to users anywhere in the world.
The satellites continuously broadcast a low power, one way position and time signal to users throughout the world. There are currently 29 satellites in orbit, called a constellation, with five spares, which assures the availability of 24 operational satellites.
GPS Satellite Network An individual GPS Satellite
User Segment: The user end of the system is basically GPS receivers that convert satellite signals into position, velocity, and time estimates. The concept is based on satellites acting as reference points and users determining their position on the earth by measuring their distance from a group of satellites. The receivers measure the time delay for the signal to reach the receiver, which gives the distance from the satellite. This information is processed to solve for ground position, velocity, and time. The receivers are compact devices that can be held in hand. A standard GPS receiver will not only place US on a map at any particular location, but will also trace our path across a map as we move. If we leave our receiver on, it can stay in constant communication with GPS satellites to see how our location is changing. With this information and its built-in clock, the receiver can give us several pieces of valuable information:
· How far we have traveled (odometer)
· How long we have been traveling
· Our current speed (speedometer)
· Our average speed
· A trail showing us exactly where we have traveled on the map
· The estimated time of arrival at our destination if we maintain our current speed