What Is GPS anyway?
The Global Positioning System is a space based navigation system. A
constellation of 24 satellites orbit the earth every 12 hours at an altitude of 14,000 miles from the center of the earth. Each satellit is armed with four atomic clocks, which keep the time to a superlative degree of accuracy. They each broadcast their precisely timed radio signals through the atmosphere and onto the earth's surface at the speed of light. The signals from each satellite arrive at any particular point on or above the earth's surface at slightly different times. This timing is proportional to the distance between the satellite and that particular point. Thus each radio beam acts as a 10,900 nautical mile long ruler.
How does it work?Trigonometry
The receiver contains a sensitive antenna and a timetable for the satellites. It measures the time difference between the arrivals of the signals and compares it with the timetable. With the application of trigonometry, the longitude, latitude and altitude of the receiver can be calculated. As with all trigonometric calculations, three satellites are needed to calculate the longitude and latitude, and a fourth satellite is needed to calculate the altitude. Further satellites simply increase the accuracy.
Datum's
Further computations are needed to take into account the fact that the world is not that round, but is an oblate spheroid that is very slightly pear shaped. This is fundamentally important if a GPS receiver is being used to read or make a map to within 1000 meter accuracy level. When setting up a GPS for map reading the most important thing to do for accuracy is to set up the grid and the datum. A detailed map will have this written somewhere in the border of the map.
How accurate is it?
Selective Availability
As GPS is currently sustained and operated by the U.S. Department of Defense (DOD), selective availability (where civilian receiver's accuracy was limited to 150 meters but the military's receiver's had a accuracy of less than 4 meters) was ended by President Clinton in 2000. For the time being civilian GPS is as accurate as military GPS.
Who uses GPS?
GPS is used to support land, sea, and airborne navigation, surveying, geophysical exploration, mapping and geodesy, conservation research, habitat modelling, vehicle location systems, farming, transportation systems, archaeology, mountaineering, fishing and a wide variety of other additional applications, such as logistic regression modeling of multitemporal Thematic Mapper data for burnt area mapping and much more.Handheld gps receivers are being used by hunters, fisherman, hikers, and outdoor sportsmen of all types for numerous applications. Motorists can do away with the fear of being lost by placing a car gps unit in their mode of transportation. Boaters and Seamen can navigate easily with a quality marine gps unit. Aviation has advanced to a new level as pilots navigate with the precision of aviation gps units. As the knowledge of the usefulness of the modern gps receiver increases, so will it's demand. So get on board, purchase your gps unit today from The GPS Depot
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