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What Is Gps?
By Mark Hamilton
GPS stands for Global Positioning System. It is a satellite radio navigation system built by the United States Department of Defense. Research on the system began in the 60’s and the first satellite was launched in 1978. It took a while for the entire system to come online but finally on April 27, 1995 it became fully operational. At first, the network was only for military use but in the 80's the United States government authorized the general public to make use of it too.
The network is composed of:
Satellites
Earth Monitoring Stations
GPS receivers
What is a Satellite?
There are currently 24 satellites orbiting the earth is 6 distinct trajectories. Each satellite completes two orbits around the earth each day, traveling at a speed of about 7,000 MPH. At the highest point in their orbit they are over 12,000 miles above the earth. From this height, the satellite signals can be received over a large percentage of the surface of the earth. A unit works by receiving multiple satellite signals and calculating the receiver's position based on triangulation of the different signals. Accuracy is increased with each additional satellite signal that is received so the orbits of the satellites are set so that at most points on the earth there are at least 4 signals that can be received. Of course, this is in theory only since the landscape around you can block some or all of the signals.
What is a Earth Monitoring Station?
There are four unmanned monitoring stations in the US and one manned master station which is located in Colorado Springs, Colorado. The four unmanned stations relay position data from the satellites to the master station. The master station uses the relayed information to correct the position of the sat tiles and sends the corrected information back to the satellites. This synchronizes the data that each satellite transmits to your receiver and ensures that your receiver is always working with accurate information.
What is a Receiver?
GPS satellites transmit low power radio signals
that can only be picked up if your unit has a direct "line of sight" to the satellite. The signals can penetrate things like glass, plastic and clouds but not solid structures like buildings or rocks. A unit works by triangulating your location based on the position of at least three satellites in the system. It compares the time it takes to receive a signal from each of the satellites in range and calculates your location based on the data.
If you are only able to pick up three satellite signals, your unit can report your location in latitude and longitude. However, when the unit picks up signals from at least four satellites it also calculates your altitude. Now it can report your trip distance, distance to a destination, travel speed and even your altitude if your receiver features an altimeter.
How accurate a unit is depends on its ability to find and lock onto a satellite’s signal. As you might expect, you get what you pay for and the more expensive units are generally more accurate. The best consumer units claim accuracy to within a few feet while the older or less expensive units can be off up to 30-40 feet or more. Where you plan to use your receiver could determine if it's worth shelling out the extra money for increased accuracy. If you're using your unit in flatter terrain with a good open view of the sky a less expensive unit could perform nearly as well as the top of the line receiver. However, if you plan to use your receiver in dense tree cover, while hiking in ravines or narrow valleys, or among tall buildings you'll gain much better accuracy with a more higher end unit.
Now you know the basics about how works and can answer the question "What is GPS?". Article Source: http://www.NewArticlesOnline.com ©2007, Mark Hamilton. Read more about handheld at HandheldGPSInformation.com.
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