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How Does GPS Work ?

How Does GPS Work ?. The Global Positioning System. 24+ satellites 20,200 km altitude 55 degrees inclination 12 hour orbital period 5 ground control stations Each satellite passes over a ground monitoring station every 12 hours. Instantaneous positioning with GPS. Your location is:

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How Does GPS Work ?

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  1. How Does GPS Work ?

  2. The Global Positioning System • 24+ satellites • 20,200 km altitude • 55 degrees inclination • 12 hour orbital period • 5 ground control stations • Each satellite passes over a ground monitoring station every 12 hours

  3. Instantaneous positioning with GPS Your location is: 37o 23.323’ N 122o 02.162’ W Accuracy of • +/- 10 m (30 ft) error (horizontal) • +/- 15 m (45 ft) error (vertical)

  4. High-precision GPS D • -Use the carrier phase, not pseudorange • Dual-frequency receivers (to remove ionosphere) • High-precision orbital information • Good monuments • Multiple stations (to remove satellite clock variations) • Sophisticated processing software • Collect lots of data

  5. High-precision systems for field surveying Movable tripod with choke-ring antenna Trimble 5700 geodetic receiver with flat antenna Monument stability and centering and leveling the antenna are critical !

  6. Method of Operation • Global positioning system (GPS) • Receiver determines location, speed, direction, and time • 3 satellite signals are necessary to locate the receiver in 3D space • 4th satellite is used for time accuracy • Position calculated within sub-centimeter scale

  7. Atmospheric Delays Ionosphere Troposphere • Ionosphere (use dual frequency receivers) • Troposphere (estimate troposphere)

  8. Multipath ‘echoes’ • Similar issue to ‘ghost’ images on TV • Causes inaccurate measurements • If we were outside right now, what would cause potential multipath errors?

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