Coastal Navigation using GPS by HC120622194747


									Session III
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.
Signal Quality and Accuracy

               The height of the bars
                in display shows
                signal strength from
                each satellite
               The “clock face”shows
                the positions of satellites
                currently in view to your
 Horizontal Dilution of Precision
                         Horizontal Dilution
                          of Precision (HDOP)
                          is a measure of
 Good                     satellite fix
Geometry                  geometry quality
                         Figure at far left has
             Poor         lower (better) HDOP
                         GPS receivers
                          measure and
                          display HDOP
Estimated Position Error
 Many  GPS units display EPE instead
 of HDOP
 – It’s an expression of the diameter
   of a circle in which your position
   target exists
 – EPE is expressed in feet or meters
   – user choice

 GPS   with SA on - 100 meters
 GPS with SA off - 10 meters(33 ft) 95%
  of time
 DGPS – approx 10 feet, 95% of time
 WAAS – approx 8 feet, 99.85% of time
  Always validate
satellite reception &
  accuracy before
using your GPS set
   for navigation.
GPS Setup Parameters
 – True or Magnetic Direction
 – Nautical/Statue Miles
 – Clock –24hrs
 – Speed in Knots
 – Variation – 013°West
 – Altitude
 – Horizontal Datum – WGS84
 – Lat & Lon – Degrees°/Minutes'/Seconds"
  Course and Bearings

Select   a heading format:
    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,
not the GPS.

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

Select   a time format:
   12 or 24 hour clock format
 –UTC or Local time

When you are using GPS on
a boat, set the speed unit
of measure to KNOTS
– Nautical Miles Per Hour.

Some GPS receivers are Automatic,
some have to be done manually.
Variation is found on the inside of the
compass rose.
        Horizontal Datum


   WGS-84   is the US standard, NAD-27 is common.
        LAT. & LON.

         Set GPS Unit to

    074 – 23 - 39.0

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

Tenths   of Minutes to Seconds
     .650 X 60 = 39.0

Seconds   to Tenths of Minutes
     39.0 ÷ 60 = .650
     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 chart datum
  i.e. Feet, Meters or Fathoms
Soundings in Fathoms
  Your depth-finder shows
the depth of water below you
now, not where your going!!!

•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.
Session III

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