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Coastal Navigation using GPS

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Coastal Navigation using GPS Powered By Docstoc
					Session 7
  GPS
Orientation
   ONE
Outline of Presentation
 GPS, how it works & what you
  need to check.
 Basic receiver functions –
  what is it telling you?
 Selecting a GPS receiver.
      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.
5 ft wide
17.5 ft long
1,860 lbs
Delta II
Confused yet?
How GPS works
 in a few logical
       steps
The basis of GPS operation is „triangulation”
from the overhead satellites in view.
   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.
  In order to
measure time
  of travel, a
GPS set needs
very accurate
time which is
achieved with
     some
  electronic
    tricks.
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.
All delays that the
    GPS signal
experiences as it
 travels through
 the atmosphere
     must be
    corrected.
ANIMATION
         Specifications

Accuracy
 GPS   10 meters(33 ft) 95% of time

 DGPS   < 10 meters (33 ft)

 Availability--99.85%   of time

 Coverage--world   wide
           SUMMARY
 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 quality
                from each satellite
               The number of items
                show the positions of
                satellites currently in
                view to your GPS.
Dilution of Precision
             Dilution of
              Precision (DOP)
              is a measure of
 Good         satellite fix
Geometry      geometry quality
             Figure at far left
              has lower (better)
              DOP Poor
                   Geometry
             GPS receivers
              measure and
              display DOP
Estimated Position Error
        “EPE”
 Many  GPS units display EPE
 – It uses satellite geometry plus
   other calculations to improve
   accuracy of the estimated position
   error
 – EPE is expressed in feet or meters
   – user choice
                    CEP = Circular Error Probable
                    SEP = Spherical Error Probable




SA – Selective Availability Error
         24 hours                   24 hours
         5/1/2000                   5/2/2000




         With

                95 % of the time
within 45 meters          within 6.3 meters
   or 148 Feet                 or 21 Feet
          DGPS
  (operated by USCG)
enables local corrections
        for errors
 DGPS                        Series of
                              coastal stations
                              broadcast
                              corrections to
                              GPS signal.
                             Former RDF
                              stations used
                              for this purpose.
                             Accuracy
                              improved to
Note: Stations on Great       better than 10
Lakes not shown on this       meters.
      illustration
WAAS – Wide Area Augmentation
          System




System of ground-based reference stations
and two stationary satellites that broadcast
precision differential GPS corrections.
Typical GPS with SA OFF)



 Be sure that the GPS
that you purchase has
WAAS
            Less than 10
  WAAS capability.
             feet of error



       Typical DGPS
Other things to
consider when
buying a GPS
     set.
         Intended Use

How are you going
Imagine your worst case scenario:

 to adjust
 – Stormy conditions. or read
 – Waves beating on the hull.
 – your GPS set in
   Boat bouncing back and forth.
 – Windshield covered with salt spray.
 – You can‟t conditions?
these let go of the helm without
    losing control of your boat.
 Mounting Capability
 Think about the
Mount near the helm.
You can‟t just lay the GPS
Swivel capability so that it can be
magnetic influence
          on the dash.
used or read by others.
Adjustable for sun glare.
that your GPS has
              your weather.
 Think offrom theworst case
Protected
on your compass!
            scenario.
Ability to view satellites.
           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 can‟t clearly read the screen at
  an arm‟s length, you won‟t be happy
  with the set in stormy conditions.
RayNav 300
     Waterproof versus
       Submergible
Waterproof means that the device will
 survive a little dampness.
Water Resistant means it won‟t last
 long in a moist, damp marine
 environment.
Submergible means that the device
 will survive a dunking in the ocean.
       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.
      12v Attachment

Be  sure your set comes
 with a power cord that
 will attach to your boat‟s
 12V system.
Carry spare batteries for
 backup.
Key and Keyboard Size

Keys  too small for your
 fingers.
Lack of keys.
The argument for pre-
 planning your trips.
GPS Age and Processor Size
The faster a GPS calculates, the
 Smaller computing
more accurate the data that it
  capability.
generates.
 Slower to calculate.
Most GPS projections are averages
of past activity.
 Less options.
Should be regenerating position at
 No DGPS or WAAS.
least once per second.
         Chart Plotters
 It is not a safe practice to
 Nice  to have but not really
be gazing at a chart plotter
  necessary.
 Colored charts are a definite
monitor when you should
  plus.
  be focusing on the other
 Paper charts are easier to read in
   boats and obstructions
  bright sunlight.
           around you.
RayChart 420
         Display Clutter

 Too  much data being presented on a
What you eliminate
    small screen.
 Have to adjust your screen area
in the close-up to remove

 some data.
views, you also lose
Such as, depth readings, aids to
   in the wide-area
 navigation, etc.

     display views.
    Screen Capabilities

  How easy is it to switch on a GPS
Minimize your dependencyfrom one
screen. to another?
   screen
  Focus handling your boat.
Focus onon a few navigation screens
   for everyday use.
Pre-plot your trip.
  Avoid having to jump a multiple
Use a nautical chart and totrip log.
   screens for basic navigation data.
Use your GPS as a quality control
check for this process.
 Remote Antenna Need

GPS   need a clear view
 of the satellites.
May need a remote
 antenna on your boat.
Remote
   Multiplexing vs Parallel
          Receivers

    Only buy a
 Multiplexing   receivers often have
  only one channel to tune into
  satellites.
   parallel GPS
 Parallel receivers can acquire several
  satellites at a time. Come in 3 – 5 – 8

     receiver.
  and 12 channel versions.
  – More accurate processing
  – Quicker start ups.
   GPS Sensor Design

 NMEA   – National Marine
  Manufacturers Association
 Standard sensor capability to
  RADAR, Chart Plotters, Depth
  Sounders, etc.
 Not all sensors are compatible to
  other manufacturer‟s equipment.
 Check to be certain.
     Used Sets

The price is so low.
 buy new!
The best price for a
 used set is FREE.
        GPS Tips
GPS looks like a compass
GPS acts like a compass
Therefore it must be a
 compass

WRONG!!!!!!!
Any questions about?

AV Task 6-1 Differences between
GPS, DGPS and WAAS – page 139.

				
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posted:9/16/2011
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