The GPS Global Positionting System

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The GPS(Global Positionting System)
by Zsuzsanna Horváth and Lilla Csonka
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Sign posting

• General information
• History
• How it is working
• Triangulating
• Measuring distance
• Perfext timing
• Satellite position
• Error correction
• GPS in work
• Sources

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WHAT DOES IT MEAN?

• Global Positioning System
• United States Department of Defense
• It is uses constellation of between 24 and 32 of
  Medium Earth Orbit satellites that transmit
  precise microwave signals, that enable GPS
  receivers to determine their current, location
  the time, and their velocity.

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General informations

• the only fully functional Global Navigation
  Satellite System in the world.
• official name NAVSTAR-GPS
• Managed by the United State Air Force 50th Space
  Wing

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History

• Based partly on similar ground-based radio
  navigation systems developed in the 1940s.
• LORAN
• Decca Navigator
• 1957 Additional inspiration came with the Sputnik
• 1960 The first satellite navigation system
• 1967 Timation satellite
• 1970s Omega Navigation System
• 1978 Block-I GPS
• 1983 available for civilian use
• 2008 GLONASS, Gallileo, COMPASS, IRNSS

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The Basic Concept

• A GPS receiver calculates its position by
  carefully timing the signals sent by the GPS
  satellites high above the Earth.
• Each satellite continually transmits messages
  containing the time the message was sent, precise
  orbital information and the general system health
  and rough orbits of all GPS satellites (the
  almanac).

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The Basic Concept

• The receiver measures the transit time of each
  message and computes the distance to each
  satellite.
• Geometric trilateration is used to combine these
  distances with the location of the satellites to
  determine the receiver's location.

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The Basic Concept

• The position is displayed, perhaps with a moving
  map display or latitude and longitude elevation
  information may be included .
• Many GPS units also show derived information such
  as direction and speed, calculated from position
  changes.

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How GPS works in 5 logical steps?

• 1. Triangulation
• 2. GPS receiver measures distance
• 3. Measure travel time
• 4. Where the satellites are in space?
• 5. Correct for any delays

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Triangulating

• Step 1 measure our distance from satellite 1
• Step 2 measure our distance to a second
  satellite
• Step 3 make a measurement from a third satellite

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2. Measuring distance

• The Big Idea Mathematically
• The problem is measuring the travel time
• Timing is tricky
• We need precise clocks to measure travel time
• The travel time for a satellite right overhead is
  about 0.06 seconds
• The difference in sync of the receiver time minus
  the satellite time is equal to the travel time

Velocity (60 mph) x Time (2 hours) Distance
(120 miles)
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3. Perfect timing

• Atomic Clocks
• use the oscillations of a particular atom as
  their "metronome."
• Extra Measurement Cures Timing Offset

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4. Satellite position

• Knowing where a satellite is in space
• A high satellite gathers no moss
• Getting the message out

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5. Error correction

• Ionosphere
• Troposphere
• Error Modeling
• Problems at the satellite

Satellites are precise but not perfect
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Errors 1
Ionospheric effects
Tropospheric effects
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Errors 2
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GPS in work

• scientists
• sportsmen
• farmers
• soldiers
• pilots
• make their work more productive
• safer
• sometimes even easier

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Sources

• Wikipedia
• http//www.trimble.com/gps/howgps.shtml