Coastal Navigation using GPS

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GPS Orientation
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THE OFFICIAL NAME IS
NAVISTAR GPS
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NAVISTAR GPS
NAVIgatonal System using Timing
And Ranging Global Positioning System
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• GPS is a satellite navigation system developed
  by the US Dept. of Defense
• (DOD)

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GPS provides continuous, all-weather,
three-dimensional positioning information
(position, speed and time)
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How does GPS work?

• GPS is a satellite navigation system developed by
  the US Dept. of Defense (DOD).
• GPS provides continuous, all-weather,
  three-dimensional positioning information
  (position, velocity and time).
• GPS is used by aviators, mariners, surveyors,
  truck and auto operators, and hikers.

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5 ft wide 17.5 ft long 1,860 lbs
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Delta II
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Confused yet?
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How GPS works in a few logical steps
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The basis of GPS operation is triangulation from the overhead satellites in view.
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In order to triangulate, your GPS receiver measures the distance from a satellite using the time of travel of the radio signals from the satellite.
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In order to measure time of travel, a GPS set needs very accurate time which is achieved with some electronic tricks.

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Along with the distance, the satellite
must know exactly where it is positioned in
space at all times. High orbits and
careful monitoring are required.
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All delays that the GPS signal experiences as it travels through the atmosphere must be corrected.
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ANIMATION
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Specifications

• Accuracy
• GPS 10 meters(33 ft) 95 of time
• DGPS lt 10 meters (33 ft)
• Availability--99.85 of time
• Coverage--world wide

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SUMMARY

• GPS Fixes are not error free
• User and/or Satellite clock bias.
• Satellite signal can be blocked.
• Atmospheric interference is possible.
• Poor satellite geometry is possible.

You must monitor these errors on your GPS
receiver.
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Signal Quality and Accuracy

• The height of the bars in display shows signal
  quality from each satellite
• The number of items show the positions of
  satellites currently in view to your GPS.

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Dilution of Precision
Good Geometry
Poor Geometry
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Estimated Position ErrorEPE

• Many GPS units display EPE
• It uses satellite geometry plus other
  calculations to improve the accuracy of the
  estimated position error.
• EPE can be expressed in feet or meters. It is a
  user choice.

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CEP Circular Error Probable SEP Spherical
Error Probable
SA Selective Availability Error
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DGPS (operated by USCG) enables local
corrections for errors
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DGPS

• Series of coastal stations broadcast corrections
  to GPS signal.
• Former RDF stations used for this purpose.
• Accuracy improved to better than 10 meters.

Note Stations on Great Lakes not shown on
this illustration
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24 hours 5/1/2000
24 hours 5/2/2000
With
95 of the time within 45 meters
within 6.3 meters or 148 Feet
or 21 Feet
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WAAS Wide Area Augmentation System
System of ground-based reference stations and two stationary satellites that broadcast precision differential GPS corrections.
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Be sure that the GPS that you purchase has WAAS capability.
Typical GPS with SA OFF)
WAAS

Less than 10 feet of error
Typical DGPS
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Other things to consider when buying a GPS set.
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Intended Use
How are you going to adjust or read your GPS set in these conditions?

• Imagine your worst case scenario
• Stormy conditions.
• Waves beating on the hull.
• Boat bouncing back and forth.
• Windshield covered with salt spray.
• You cant let go of the helm without losing
  control of your boat.

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Mounting Capability
Think about the magnetic influence that your GPS will have on your compass!

• Mount near the helm.
• Swivel capability so that it can be used or read
  by others.
• Adjustable for sun glare.
• Protected from the weather.
• Ability to view satellites.

You cant just lay the GPS on the dash. Think of your worst case scenario.
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Screen Size

• Can you read the display at a distance?
• Avoid sets with tiny numbers and letters.
• Some sets sacrifice readability for more chart
  area on their screens.
• If you cant clearly read the screen at an arms
  length, you wont be happy with the set in stormy
  conditions.

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Waterproof versus Submergible

• Waterproof means that the device will survive a
  little dampness.
• Water Resistant means it wont last long in a
  moist, damp marine environment.
• Submergible means that the device will survive a
  dunking in the ocean.

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Display Lighting

• Buy a back-lighted display so you can view it at
  night,
• Color displays are usually easier to read than
  black and white.
• Viewable in bright sunlight.
• Glare resistant screen.

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12v Attachment

• Be sure your set comes with a power cord that
  will attach to your boats 12V system.
• Carry spare batteries for backup.

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Chart Plotters
It is not a safe practice to be gazing at a chart plotter monitor when you should be focusing on the other boats and obstructions around you.

• Nice to have but not really necessary.
• Colored charts are a definite plus.
• Paper charts are easier to read in bright
  sunlight.

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Remote Antenna Need

• GPS need a clear view of the satellites.
• May need a remote antenna on your boat.

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Remote
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Used Sets

• The price is so low. buy new!
• The best price for a used set is FREE.