Differential GPS
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The advantages of differential GPS location calculations.When you calculate the distance to six satellites, you can draw six circles which will intersect each other at a specific point. The GPS receiver will create all its distance calculations by using a built in clock, and the distances will be correct in proportion to each other. Differential GPS can help correct certain errors which you may have. The job of the receiver is to make modifications which will cause the spheres to intersect each other. The receiver must set its own clock so that it is the same as the satellite. Because of relativity, the atomic clock on the satellite may be a few microseconds faster than the clock on the receiver. Because of this the receiver clock has to constantly keep itself in sync with the atomic clock on the satellite. It is important that the receivers keep up with the location of the satellite, and each GPS receiver has a type of storage system where it determines the location of a satellite and where it should be at any given time. While the gravitational pull of the sun and moon effect the orbit of the satellites, these adjustments are sent by the Department of Defense to GPS receivers. This system works well, but there are sometimes errors. It is assumed that radio signals will travel through the atmosphere at a constant speed (the speed of light), but this is not always the case. The atmosphere of the earth slows down the radio signals, and problems can occur if these signals if radio waves bounce off buildings and other structures. These signals confuse receivers into making them think the satellite is farther away than it is, and sometimes the satellites themselves send out bad signals. Differential GPS corrects these errors by routing the signals from satellites through a stationary location which has the DGPS hardware. It is capable of correcting any errors in the signal. This insures that the GPS receiver gets a correct signal which is highly accurate. DGPS receivers are much better than normal receivers because of this. The most important role of differential GPS is to correct the signals sent by satellites through the atmosphere. Radio signals run into problems when entering the ionosphere and these signals must be corrected when they reach the surface. Many GPS units are capable of transferring data into a computer, so that you can keep digital copies of maps for future use. The newer navigational systems have become much more user friendly. |
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