Coastal%20Navigation%20using%20GPS

1
Session 7 GPS Orientation ONE
2
Outline of Presentation

• GPS, how it works what you need to check.
• Basic receiver functions what is it telling
  you?
• Selecting a GPS receiver.

3
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.

4
5 ft wide 17.5 ft long 1,860 lbs
5
Delta II
6
(No Transcript)
7
(No Transcript)
8
Confused yet?
9
How GPS works in a few logical steps
10
The basis of GPS operation is triangulation from the overhead satellites in view.
11
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.
12
In order to measure time of travel, a GPS set needs very accurate time which is achieved with some electronic tricks.

13
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.
14

All delays that the GPS signal experiences as it travels through the atmosphere must be corrected.
15
ANIMATION
16
Specifications

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

17
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.
18
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.

19
Dilution of Precision

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

Good Geometry
Poor Geometry
20
Estimated Position ErrorEPE

• 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

21
CEP Circular Error Probable SEP Spherical
Error Probable
SA Selective Availability Error
22
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
23
DGPS (operated by USCG) enables local
corrections for errors
24
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
25
WAAS Wide Area Augmentation System
System of ground-based reference stations and two stationary satellites that broadcast precision differential GPS corrections.
26
(No Transcript)
27
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
28
Other things to consider when buying a GPS set.
29
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.

30
Mounting Capability
Think about the magnetic influence that your GPS has 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.
31
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.

32

RayNav 300
33
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.

34
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.

35
(No Transcript)
36
12v Attachment

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

37
Key and Keyboard Size

• Keys too small for your fingers.
• Lack of keys.
• The argument for pre-planning your trips.

38
GPS Age and Processor Size
The faster a GPS calculates, the more accurate the data that it generates. Most GPS projections are averages of past activity. Should be regenerating position at least once per second.

• Smaller computing capability.
• Slower to calculate.
• Less options.
• No DGPS or WAAS.

39
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.

40
RayChart 420
41
Display Clutter

• Too much data being presented on a small screen.
• Have to adjust your screen to remove some data.
• Such as, depth readings, aids to navigation, etc.

What you eliminate in the close-up area views, you also lose in the wide-area display views.
42
Screen Capabilities
Minimize your dependency on a GPS screen. Focus on handling your boat. Pre-plot your trip. Use a nautical chart and a trip log. Use your GPS as a quality control check for this process.

• How easy is it to switch from one screen to
  another?
• Focus on a few navigation screens for everyday
  use.
• Avoid having to jump to multiple screens for
  basic navigation data.

43
Remote Antenna Need

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

44
Remote
45
Multiplexing vs Parallel Receivers
Only buy a parallel GPS receiver.

• Multiplexing receivers often have only one
  channel to tune into satellites.
• Parallel receivers can acquire several satellites
  at a time. Come in 3 5 8 and 12 channel
  versions.
• More accurate processing
• Quicker start ups.

46
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
  manufacturers equipment.
• Check to be certain.

47
Used Sets

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

48
GPS Tips

• GPS looks like a compass
• GPS acts like a compass
• Therefore it must be a compass
• WRONG!!!!!!!

49
Any questions about?AV Task 6-1 Differences
between GPS, DGPS and WAAS page 139.