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Exploring GPS: Navigating Within and Beyond the Physics Classroom

Delve into the world of GPS technology with this informative guide by Andrew McLean and Kelvin Barraclough from Gisborne Secondary College. Learn about the 24+ satellites, ground stations, signal transmission, satellite positioning, accuracy, receivers, and data gathering capabilities of GPS systems. Discover how GPS works, its applications, and the software options available for data transfer and mapping. Whether you're a physics enthusiast or simply curious about navigation technology, this resource provides valuable insights into the fascinating realm of GPS technology.

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Exploring GPS: Navigating Within and Beyond the Physics Classroom

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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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