Global Positioning Systems

1. Global Positioning Systems Glen T. Huettl Agricultural Education Garrison High School

2. Global Positioning System (GPS) • Navigation and Positioning System • Determines Exact Location • Establishes Longitude, Latitude, Altitude

3. GPS Components • Satellites in Space Send Signals • Receivers on the earth Receive the Signals • Software Converts Satellite Signals • Position Monitoring Equipment Validate Satellite Location

4. How GPS Works • Receivers calculate position by reading 3 or more satellite signals • Called “Triangulation” • Theory used before GPS to locate earthquakes

5. GPS Developed By: • U.S. Department of Defense • Available for both Civilian and Military Uses • Available 365 days a year

6. Commerical Applications • Emergency Vehicles • Electronic Maps in Cars • Aircraft Landing Systems • Delivery Vehicles • Sea Navigation

7. History of GPS • Developed by Department of Defense for Security Purposes • Previous navigational and positional methods were not exact • GPS is answer to age-old problem

8. Satellites • NAVSTAR (Navigation Satellite Timing and Ranging) • 24 Satellites • Circle the earth every 12 hours • 4 - 10 Satellites visible from any location in the earth at any time • Send radio signals

9. Satellites (cont’d) • Act as Reference Points • Position known and precisely measured • Control Segment continually monitor accuracy of signal • Atomic Clocks provide timing accuracy

10. The Satellite Signal • Information sent is 1) Time stamp of when signal sent and 2) Satellite position • Complicated digital codes referred to as “Pseudo-Random” Code • Radio signals transmit two L-Band frequencies: L1 and L2

11. Receiver • Small hand-held computers • Attach to an Antenna that receives satellite signals • Uses integrated circuit technology • Costs vary from $200 to several $1000’s • Affordable to a wide audience

12. The Receiver Calculates Position • Travel time of signals plus high powered math calculates position • Speed of Light X Time = Distance • Converts signals sent from 3 to 4 satellites • Intersecting point of three measurements gives positional reading (“Triangulation”)

13. Control Segment • Monitor Satellite Signal for Accuracy • Located around the world • Satellites pass over monitors every 12 hours • Measure signals and correct positional errors

14. Error Sources • Selective Availability • Particles in the Ionosphere • Atomic Clocks • Speed of Light Calculations • Multipath Errors • Receiver Errors

15. Error Correction Methods • Control Segment Error Correction • Differential Global Positioning System (DGPS)

16. DGPS • More advanced form of GPS • Offers more Accuracy • DGPS adds correctional signal to GPS signals • Uses a reference station to broadcast corrections to receivers

17. DGPS (cont’d) • Cancels out natural and man-made errors • Makes GPS positioning very precise • Broadens GPS applications because of accuracy of Differential signal.

18. DGPS Uses • Coast Guard • Natural Resource Management • Forest Service • Offshore Exploration • Agricultural Uses

19. Commercial USES • Yield Monitors • Variable Rate Technology • Field Mapping and Acreage Management • Noting Underground Locations

20. WAAS Wide Area Augmentation System • Government supplied correction • Approx 25 land based stations