Coastal Navigation using GPS

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Session III GPS DEPTH-FINDER UNITS
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• GPS positions 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 can monitor these errors with 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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Horizontal Dilution of Precision

• Horizontal Dilution of Precision (HDOP) is a
  measure of satellite fix geometry quality
• Figure at far left has lower (better) HDOP
• GPS receivers measure and display HDOP

Good Geometry
Poor Geometry
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Estimated Position ErrorEPE

• Many GPS units display EPE
• Its an expression of the diameter of a circle in
  which your position target exists
• EPE is expressed in feet or meters user choice

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Specifications

• Accuracy
• GPS without SA - 100 meters
• GPS with SA - 10 meters(33 ft) 95 of time
• DGPS approx 10 feet, 95 of time
• WAAS approx 8 feet, 99.85 of time

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GPS Setups

• True or Magnetic Direction
• Nautical Miles
• Clock
• Speed in Knots
• Variation
• Altitude
• Horizontal Datum
• Lat Lon

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Course and Bearings

• Select a heading format
• TRUE
• MAGNETIC

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GPS is not a Compass

• GPS reports movement over ground - often
  different than the vessels heading.
• GPS errors affect accuracy.
• Always steer off your compass.

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Distance
When you are using your GPS on a boat, set the
Distance Unit of Measure to Nautical Miles.
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Time Format

• Select a time format
• 24 hour clock format
• 12 hour clock format

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GPS Time Setup

• Select a Time Setup.
• UTC
• Local time

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Speed
When you are using GPS on a boat, set the speed
unit of measure to KNOTS Nautical Miles Per
Hour.
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Variation
Some GPS receivers are Automatic, some have to
be done manually Variation is found on the
inside of the compass rose.
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Altitude Mode
Set your GPS for the height of your GPS antenna
at sea level.
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Horizontal Datum
Update your GPS with the HORIZONTAL DATUM
referenced on the nautical chart that you are
using. WGS84
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Horizontal Datum
WGS84
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Selecting the correct Datum

• WGS-84 is the standard in US waters, NAD-27 is
  common. Different datums are used in foreign
  waters.
• Becomes more important as local datum become
  increasingly offset from WGS-84.
• Shown on the General Information Blocks of most
  charts/maps.

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LAT. LON.
Set GPS Unit to

• Degrees-Minutes-Seconds 074 23 - 39.0

Most units are set
Degrees-Minutes- Tenths of Minute
074 23 .650
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• CONVERSIONS

• Tenths of Minutes to Seconds
• .650 X 60 39.0

• Seconds to Tenths of Minutes
• 39.0 60 .650

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DEPTH-FINDER
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Depth Measurement
Set your depth sounder to correspond to the
vertical datum referenced on the nautical chart
that you are using.
Depth-Finder should be set for charti.e. Feet,
Meters or Fathoms
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Soundings in Fathoms
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Vertical Datum

• Units of Measure
• - Feet
• - Fathoms
• - Meters

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REMEMBER Your depth-finder shows
the depth of water youre in, not where
youre going!!!
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TRANSDUCER

• It is very important to know where the transducer
  is mounted
• You need to know the distance from your waterline
  to the transducer
• You also need to know the distance from the
  transducer to the lowest point of your boat.

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Remember that the greatest hazard to navigation
may be a bored navigator!!!!!!!!
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END OF Session III