GK-12 Sensors!: GPS

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GK-12 Sensors! GPS

• Brad Neumann and Eeva Hedefine
• The University of Maine

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What is GPS?

• GPS Global Positioning System
• Have you ever been in a shopping mall and relied
  on the directory maps with the You Are Here
  star?
• GPS works the same way,
• but on a global scale.

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But, how does GPS work?

• Just as we depend on satellites for cellular
  phones and TV broadcasts, we also rely on
  satellites for GPS.
• In fact, GPS relies on 24 satellites that orbit
  the earth in very precise paths.

www.stoller-eser.com
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How does GPS work?

• Imagine that a GPS unit communicates with only
  one of these 24 satellites.
• Then, the GPS can only make a large and general
  You Are Here star.

www.stoller-eser.com
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How does GPS work?

• With two, and even three
• and four satellites to
• communicate with, the
• GPS unit can make the
• You Are Here star smaller
• and more precise.

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How does GPS work?

• Communication with four satellites is usually
  enough to improve location accuracy to within
  about 10 meters.
• Some GPS units can provide location within a few
  centimeters!

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Components of a GPS

• Three parts of a GPS
• Space Segment
• satellites
• Control Segment
• base stations
• User Segment
• fighter jet
• surveyor
• hiker

www.aero.org/publications/GPSPRIMER/GPSElements.ht
ml
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Space Segment

• 24 satellites in 6 orbital planes
• Satellites orbit at an altitude of 12,000 miles
• Each satellite orbits the earth in 12 hours
• Each satellite broadcasts a signal

www.stoller-eser.com
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Control Segment

• Base station receives signal and monitors each
  satellites exact location in space.
• Base station also maintains an atomic clock for
  precise measurements of signal travel time.

www.stoller-eser.com
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User Segment

• To determine location, the receiver measures the
  time it takes for the individual signals to reach
  the unit.
• distance travel time X speed of light
• Through communication with multiple satellites
  the receiver location can be triangulated

www.stoller-eser.com
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How do I know where I am?

• The GPS receiver displays location in degrees of
  latitude and longitude.
• Latitude is measured north and south of the
  equator.
• Longitude is measured east and west of the prime
  meridian.

www.stoller-eser.com
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Global Positioning System

• Initially developed by the U.S. Department of
  Defense for military use.
• Still maintained by DOD today, but can also be
  for civilian use.
• Navigation in your car.
• Finding your favorite fishing hole.
• Mapping trails or roads.

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GPS Accuracy

• For safety reasons the DOD only operated civilian
  GPS with selective availability scrambling of
  signal
• Selective availability was turned off in May of
  2000.
• GPS accuracy went from 100 m to 10 m in good
  conditions.
• The most accurate (and expensive) GPS receivers
  now have centimeter accuracy.
• Accuracy depends on
• Quality of equipment
• Time over which observations are made

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GPS Accuracy
www.stoller-eser.com

• Accuracy is best when the satellites used are
  widely spaced

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GPS in the Real World

• Navigation
• Military, commercial, personal
• Locational data collection
• Science
• Relate a particular phenomenon to a place
• Business - car rental companies
• Track cars if stolen
• Fine customers for traveling outside state
  boundaries or speeding
• Mapping
• Geographic Information Systems (GIS)

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GPS in the Real World
Digital Angel

• Digital Angel
• Locate and track people using GPS
• Monitor vital signs with biosensors
• Temperature
• Pulse
• Can determine whether a person has fallen down
• Verichip
• Implantable chip
• Stores unique ID
• Can link ID to stored health data

msnbc.msn.com
www.howstuffworks.com
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Garmin eTrex
PAGE Button
UP Button
DOWN Button
POWER Button
ENTER Button
www.garmin.com/products/etrex/
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Global Positioning Systems

• Lets get out there and try one out!
• References
• http//msnbc.msn.com/id/6237364. MSNBC
• http//www.aero.org. The Aerospace Corporation
• http//www.howstuffworks.com/location-tracking.ht
  m. HowStuffWorks
• http//www.garmin.com/products/etrex/. Garmin
  eTrex
• http//www.stoller-eser.com. Environmental
  Surveillance, Education, and Research Program.
  Idaho
• National Engineering and Environmental Laboratory