GPS: History, Technology, and Accuracy Issues

Introduction to GPS and Its Evolution

  • Discussion on the importance of completing assessments before exams to facilitate honest evaluations.
    • Mention of anonymity in evaluations.
    • Reference to a slide covering GPS information.

History of GPS

  • Initial introduction of GPS errors and user experiences.
    • Observation of GPS dots bouncing on stationary maps.
    • The existence of measurement errors inherent to GPS technology.
  • Military Origins:
    • GPS was initially funded by the military for strategic purposes.
    • Focus on navigation for naval vessels in the Pacific and ballistic missile guidance.
    • Concern for security and preventing enemy access to the technology.
    • Introduction of dual signals: one for military and a less accurate one for civilian use (Selective Access).
    • General civilian users were limited to 100-meter accuracy, typically closer to 60 meters.
  • Transition to Civilian Use:
    • Realization of GPS's utility for civilian navigation, especially in maritime scenarios.
    • Existing applications begun to expand to land navigation.
    • Incident Leading to GPS Opening:
    • Korean Air Flight 007 incident: Shot down after veering into USSR airspace.
      • Resulted in public outcry and the call for better navigational technology.
      • President Reagan's decision to open access to GPS for civilian users.
    • By 2000, improvements allowed precision to reach up to 15 meters for civilian use.
    • Commercial navigation options emerged such as Garmin and TomTom.

Current GPS Technologies

  • Modern Accuracy:
    • Raw GPS accuracy: 3 to 5 meters outdoors with a clear view of satellites.
    • Importance of precision in applications like construction and land surveying.
  • RTK (Real-Time Kinematic) Technology:
    • Use of fixed ground stations to correct satellite signals for higher accuracy.
    • Example uses in wildlife tracking, surveying, and construction.
    • Mention of US Geological Survey (USGS) markers used for setting reference points.
    • Corrections improve accuracy to centimeter levels.

Satellite and Signal Correction

  • Ground Stations and Signal Corrections:
    • Ground stations monitor satellite signals, providing real-time adjustments.
    • Data from satellites shared with GPS units for precision correction.
  • Applications Beyond GPS:
    • Mention of drone navigation for agricultural purposes and delivery systems.
    • Importance of technical accuracy for industries relying on GPS.

Sources of GPS Error

  • Satellite Clock Drift:
    • Satellite clocks are extremely precise but can drift due to various factors.
    • Estimated drift of 1 nanosecond every 3 hours, equating to approximately 32 meters of positional error.
  • Influencing Factors:
    • Locations obscure signals (trees, tunnels), affecting signal reception.
    • Seasonal variations like clouds and storms can influence GPS functionality.
  • Multipath Effects:
    • Signals bouncing off surfaces before reaching GPS receivers, creating errors through delays.

Trilateration and Geometry in GPS

  • Triangulation Concept Misunderstood:
    • Explained concept of trilateration used in GPS positioning.
    • Importance of satellite positioning and geometry for accurate readings.
    • Importance of avoiding clustered satellite positions; wider spread improves accuracy.
    • Understanding that satellite signals travel vast distances (approx. 12,000 miles).

Conclusion and Open Discussion

  • Recap on importance of understanding GPS and its implications in various fields.
  • Invitation for questions or clarifications about GPS technology and its uses.
  • Additional comments made regarding classroom dynamics and measurement accuracy issues.