Outline of Presentation

2. GPS, how it works & what you need to check. Basic receiver functions – what is it telling you? Selecting a GPS receiver. Outline of Presentation

3. 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. How does GPS work?

4. 5 ft wide 17.5 ft long 1,860 lbs

5. Delta II

9. How GPSworks in a few logical steps

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.

15. ANIMATION

16. Accuracy GPS 10 meters(33 ft) 95% of time DGPS < 10 meters (33 ft) Availability--99.85% of time Coverage--world wide Specifications

17. 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. SUMMARY 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. 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 Estimated Position Error“EPE”

21. CEP = Circular Error Probable SEP = Spherical Error Probable

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

27. Typical GPS with SA OFF) WAAS Typical DGPS

28. Other things to consider when buying a GPS set.

29. Imagine your worst case scenario: Stormy conditions. Waves beating on the hull. Boat bouncing back and forth. Windshield covered with salt spray. You can’t let go of the helm without losing control of your boat. Intended Use

30. Mounting Capability • 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.

31. 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. Screen Size

32. RayNav 300

33. Waterproofmeans 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. Waterproof versus Submergible

34. 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. Display Lighting

36. Be sure your set comes with a power cord that will attach to your boat’s 12V system. Carry spare batteries for backup. 12v Attachment

37. Keys too small for your fingers. Lack of keys. The argument for pre-planning your trips. Key and Keyboard Size

38. Smaller computing capability. Slower to calculate. Less options. No DGPS or WAAS. GPS Age and Processor Size

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

40. RayChart 420

41. 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. Display Clutter

42. 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. Screen Capabilities

43. GPS need a clear view of the satellites. May need a remote antenna on your boat. Remote Antenna Need

44. Remote

45. 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. Multiplexing vs Parallel Receivers

46. 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. GPS Sensor Design

47. The price is so low. buy new! The best price for a used set is FREE. Used Sets

48. GPS looks like a compass GPS acts like a compass Therefore it must be a compass WRONG!!!!!!! GPS Tips

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