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GPS

GPS. How it Works For a full tutorial on GPS and its applications visit the Trimble Website. What is GPS?. Global Positioning System is a worldwide radio-navigation system formed from a constellation of satellites Dependent on line of sight. GPS Systems.

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GPS

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  1. GPS How it Works For a full tutorial on GPS and its applications visit the Trimble Website

  2. What is GPS? • Global Positioning System is a worldwide radio-navigation system formed from a constellation of satellites • Dependent on line of sight

  3. GPS Systems • NAVSTAR (Navigation System Timing and Ranging) • United States • GLONASS • Russian Global Navigation SS • GALILEO • European Union • COMPASS (BeiDou) • Chinese Navigation System • IRNSS • Indian Regional Navigational SS

  4. Components of GPS • Space • Satellites • Control • Ground control and antennas and monitoring stations • User • Military, civil, commercial, scientific

  5. Satellites (SV’s) • 32 satellites • Orbit at 12,600 miles • Six orbital planes • Each SV has a ½ sidereal day orbital period • ~ Nine satellites are visible at any given time Garmin

  6. Control Segment

  7. Users • Civilian • Cartography, Cellular networks, fleet tracking, navigationetc. • Military • Navigation, target tracking, munitions guidance, and reconnaissance • Nuclear detonation detectors

  8. How do we determine our position? • We have to determine our precise distance to at least 4 GPS satellites • We need extremely accurate clocks • In addition to distance we need to know exactly where the satellites are in space. • Lastly, we correct for any delays the signal experiences as it travels through the atmosphere.

  9. How GPS works

  10. Information sent in the GPS signal • GPS timing signal (PRC) • Ephemeris • Satellite orbit information • Updated every 2 hours valid for 4 hours • Almanac • Orbit and status for all 32 satellites • Error corrections

  11. Sync Satellite and Receiver • We need to have an accurate measure of the radio signal travel time • Atomic Clock • Use oscillations of an atom for timing • A fourth measurement is used to determine the position • The receiver looks for a single correction factor that it can subtract from all its timing measurements that would cause them all to intersect at a single point

  12. Correcting Errors • Charge particles in the ionoshpere and water vapor in troposhpere slows the GPS signal • Multipath error • Tiny errors that occur at the satellite • Selective Availability

  13. Differential GPS • Relies on the operation of two receivers • One is stationary and its location is know precisely • The second is roving and making measurements (this is YOU!) • The reference station “knows” where it is located • It uses that information to correct the timing from the GPS satellite • This error correction is then sent to the rover to correct the measurements

  14. Wide Area Augmentation System • WAAS • Uses ground stations to measure the variation in the GPS system • It corrects for this error and sends the correction to WAAS satellites • Must have a specially equipped receiver to obtain the WAAS signal • Typically accurate to within 1 meter

  15. Real Time Kinematic • RTK • Based on the use of carrier phase measurements • RTK systems use a base station that transmits the measure carrier phase to mobile individuals • Can result in cm accuracy

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