| GPS is the abbreviation for the Global Positioning | | | | responsible for relaying position data from the |
| System which is a satellite navigation system | | | | satellites to the master station. The master |
| designed and built by the United States | | | | station uses this data to correct the position of |
| Department of Defense. It was first conceived in | | | | the sat tiles which is then transmitted back to the |
| the 1960's and the first GPS satellite was launched | | | | satellites. This keeps the data that the satellites |
| in 1978. This navigation system became fully | | | | transmit synchronized to provide accurate |
| operational in 1995 and was used exclusively by | | | | coordinate information |
| the U.S. Military until the U.S. government | | | | The GPS receiver is the device that we are all |
| authorized its use by the general public. | | | | familiar with. In the car, hand-held units, data |
| The GPS network is really just composed of | | | | collectors, and GPS surveyor equipment all make |
| three things: | | | | use of the Global Positioning System. They |
| 24 Satellites | | | | receive a low power radio signal from the |
| Earth Monitoring Stations | | | | satellites overhead if they are in line-of-sight. |
| GPS Receivers | | | | A GPS receiver triangulates its position based on |
| The 24 satellites orbit the earth in 6 distinct | | | | the position of at least three satellites. It calculates |
| trajectories. They orbit the earth twice a day at | | | | your position by comparing the time it takes your |
| around 7,000 miles per hour at a distance of | | | | receiver to receive the signal from each satellite. |
| 12,000 miles. This allows their signals to be | | | | 3 satellites will allow your GPS unit to calculate |
| received over a large percentage of the earth's | | | | your coordinates in latitude/longitude while four or |
| surface. The more satellite signals a GPS unit | | | | more satellites will also allow it to calculate altitude. |
| receives the more accurately it can calculate its | | | | With this information the current generation of |
| position by triangulating the signals. The satellites | | | | GPS devices can calculate your trip distance, |
| orbits are placed so that nearly every part of the | | | | distance to your destination, how fast you are |
| earth is receiving 4 signals at all times. Of course | | | | going, and your altitude. |
| landscape and groundcover can affect this. | | | | As you can see the GPS systems in place today |
| The GPS earth monitoring stations, of which there | | | | provide a very useful tool to anyone who wishes |
| are 4 unmanned and 1 master stations, are | | | | to tap into its network. |