Global Positioning System

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Global Positioning System

• How does GPS work?
• By Brian Patrick
• with additions by
• Steve McCarville

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Step 1

• Triangulation from 24 satellites in active orbit
  are the basis of the GPS
  
• Radio signals are sent from orbiting satellites
  to Earth
  

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Step 2

• A GPS receiver measures distance using the travel
  time of radio signals from the ground to
  satellites.
  
• GPS radio signals are between 1,227 1,575
  megahertz.

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Step 3

• In order to measure the travel time between the
  ground and the satellite, GPS uses very precise
  clocks.
  
• However, ground receivers are not as accurate as
  the clocks on the satellite.
  
• Slight timing differences may occur.

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Step 4

• Distance is not the only thing that needs to be
  known.
  
• The exact location of the satellites are needed.
• However, sometimes due to orbital errors,
  inaccuracies may occur.

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Step 5

• As the GPS signals travel through the atmosphere,
  delays occur.
  
• GPS accounts for the delays and delivers the
  desired information into position, velocity, or
  time information.
  

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How Accurate is GPS?

• GPS interferences include
• Atmosphere
• Reflection of signals (buildings, etc.)
• Clock errors
• Number of satellites visible (signal may be
  blocked due to buildings, foliage, electronics,
  etc).
  
• Selective Availability

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How Accurate is GPS?

• Todays GPS receivers are very accurate.
• Garmin Ltd. boast a precision of 15 meters, on
  average.

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GPS Video

• Click on this web link and watch How Stuff
  Works use a GPS while hiking.
  
• How Stuff Works and GPS

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Works Cited

• http//www.mitre.org/
• http//www.garmin.com/
• http//www.trimble.com/
• http//www.garmin.com/manuals/GPSGuideforBeginners
  _Manual.pdf
  
• http//rockyweb.cr.usgs.gov/outreach/gps.html