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Andrew McLean Kelvin Barraclough Gisborne Secondary College

GPS in (and out of)the Physics Classroom. Andrew McLean Kelvin Barraclough Gisborne Secondary College. What is GPS?. 24 + satellites. What is GPS?. 24 + satellites Several ground stations. What is GPS?. 24 + satellites Several ground stations GPS receiver. Satellites.

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Andrew McLean Kelvin Barraclough Gisborne Secondary College

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  1. GPS in (and out of)the Physics Classroom Andrew McLean Kelvin Barraclough Gisborne Secondary College

  2. What is GPS? • 24 + satellites

  3. What is GPS? • 24 + satellites • Several ground stations

  4. What is GPS? • 24 + satellites • Several ground stations • GPS receiver

  5. Satellites • Altitude ≈ 20200 km

  6. Satellites • Altitude ≈ 20200 km • Period 12 hours

  7. Satellites • Altitude ≈ 20200 km • Period 12 hours • At least 4 visible everywhere

  8. Satellites • Altitude ≈ 20200 km • Period 12 hours • At least 4 visible everywhere • Solar powered, ≈ 50 W transmitter

  9. Satellites • Altitude ≈ 20200 km • Period 12 hours • At least 4 visible everywhere • Solar powered, ≈ 50 W transmitter • Transmit on 1575.42 MHz

  10. Satellites • Altitude ≈ 20200 km • Period 12 hours • At least 4 visible everywhere • Solar powered, ≈ 50 W transmitter • Transmit on 1575.42 MHz • Fitted with atomic clocks

  11. Satellites • Altitude ≈ 20200 km • Period 12 hours • At least 4 visible everywhere • Solar powered, ≈ 50 W transmitter • Transmit on 1575.42 MHz • Fitted with atomic clocks • Lifespan ≈ 10 years

  12. Ground Stations • I master station, four remote

  13. Ground Stations • I master station, four remote • Monitor satellites and send back accurate orbital and time data

  14. The Signal • The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS.

  15. The Signal • The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS. • The “ephemeris”. Accurate data of individual satellite position.

  16. The Signal • The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS. • The “ephemeris”. Accurate data of individual satellite position. • The “pseudo random code”. Effectively, an accurate time signal

  17. The Signal • The “almanac”. Approximate position of all satellites, transmitted and stored in the GPS. • The “ephemeris”. Accurate data of individual satellite position. • The “pseudo random code”. Effectively, an accurate time signal • Turned off while satellite orbit is adjusted

  18. Satellite positions 27400 km 20200 km

  19. Signal times 0.091 s 0.067 s

  20. Establishing position

  21. Establishing position

  22. Establishing position • If receiver had a good enough clock – • Two satellites – somewhere on a circle

  23. Establishing position • If receiver had a good enough clock – • Two satellites – somewhere on a circle • 3rd satellite – cuts this circle twice, but usually one solution is obvious

  24. Establishing position • If receiver had a good enough clock – • Two satellites – somewhere on a circle • 3rd satellite – cuts this circle twice, but usually one solution is obvious • 4th satellite – removes ambiguity

  25. Establishing position • With a small, cheap clock -

  26. Establishing position • With a small, cheap clock – • 3 satellites give 2D fix

  27. Establishing position • With a small, cheap clock – • 3 satellites give 2D fix • 4 satellites give 3D fix

  28. Accuracy • Given clear view of sky typically 5 – 10 m

  29. Receivers • Aren’t equal

  30. Receivers • Aren’t equal • Need “good view” of sky

  31. Possible information • Position

  32. Possible information • Position • Distance travelled

  33. Possible information • Position • Distance travelled • Speed

  34. Possible information • Position • Distance travelled • Speed • Direction

  35. Possible information • Position • Distance travelled • Speed • Direction • Altitude

  36. Gathering data – “low tech”

  37. Gathering data – “hi tech” • Almost all GPS receivers can be connected to a computer to transfer data

  38. Suitable software (1) • “OziExplorer”

  39. Suitable software (1) • “OziExplorer” • $130

  40. Suitable software (1) • “OziExplorer” • $130 • Uses raster mapping

  41. Suitable software (1) • “OziExplorer” • $130 • Uses raster mapping • Suitable for all brands of GPS

  42. Suitable software (1) • “OziExplorer” • $130 • Uses raster mapping • Suitable for all brands of GPS • Transferring data from Ozi is awkward

  43. Suitable software (2) • Garmin “Mapsource”

  44. Suitable software (2) • Garmin “Mapsource” • Free with Garmin GPS

  45. Suitable software (2) • Garmin “Mapsource” • Free with Garmin GPS • Uses Vector mapping

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