15 GPS - Introduction To GPS CE 111 GPS ~ History The...

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Introduction To GPS CE 111
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GPS ~ History The Global Positioning System was conceived, designed, and deployed by the US Department of Defense Primarily, if not solely, for military purposes Over $10 billion invested by US government NAVSTAR ( Nav igation S atellite T iming a nd R anging), the official DoD name for GPS
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What Is GPS? Earth-orbiting satellites Ground-based monitoring stations Individual GPS receivers All these make up the Global Positioning System!
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Control Segment Space Segment User Segment ~ GPS ~ Monitor Stations Ground Antennas Master Station
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Kwajalein Atoll US Space Command Control Segment Hawaii Ascension Is. Diego Garcia Cape Canaveral Ground Antenna Master Control Station Monitor Station
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Space Segment
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Surveying. Military. Search and rescue. Disaster relief. Marine, aeronautical and terrestrial navigation. Remote controlled vehicle and robot guidance. Satellite positioning and tracking. Shipping. Geographic Information Systems (GIS). Recreation. Etc. User Segment
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Position and coordinates. The distance and direction between any two waypoints or a position and a waypoint. Travel progress reports. Accurate time measurement. Four Basic Functions of GPS
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Satellite Orbits Usually 6 (at least 4) satellites are within view from any location on earth. Your Location
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How It Works Basis of GPS is “trilateration” To trilaterate: Each satellite sends radio signals (in several channels) GPS receiver “receives” and decodes signals from 4 (or 3) satellites Receiver computes distance to each satellite Signal knows the exact time it was sent and from which satellite Errors are corrected Positions are determined
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How It Works
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Time is of the essence… Remember the old word problems: If a train left Station A at noon going 60 mph, how far will it have gone at 2:00 pm? D = V x T GPS – Determine distance by how long it takes a radio signal to reach us from a satellite Radio waves travel at the speed of light
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Time is of the essence… Speed of light - 186,000 miles/second Each GPS satellite is equipped with a atomic clock accurate to 3 nanoseconds (0.000000003 s) +/- 1 second every 360,000 years Ground control stations correct satellites Satellites correct GPS receivers A discrepancy between satellite and receiver of 1/100 sec could result in an error of 1860 miles!
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Position is Based on Time T + 3 Distance between satellite and receiver = “3 times the speed of light” T Signal leaves satellite at time “T” Signal is picked up by the receiver at time “T + 3”
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How It Works Accurate timing is the key to measuring distances. Satellites are accurate because they have atomic
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This note was uploaded on 09/20/2011 for the course C E 111 taught by Professor Staff during the Spring '08 term at Iowa State.

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15 GPS - Introduction To GPS CE 111 GPS ~ History The...

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