1. Farm of the Future

2. GLONASS Russia’s global satellite navigation system 24 satellites in three orbits Five satellites visible

3. Farm of the Future What is GPS and What Does it Do? NAVSTAR GPS oNAVigation System with Time And Ranging Global Positioning System GPS is a satellite-based system that uses a constellation of 24 satellites to give a user an accurate position on Earth.

4. Farm of the Future GPS System Segments Consists of three distinct segments: oSpace Segment oControl Segment oUser Segment

5. Farm of the Future Space Segment 24 Satellites 6 Orbits 10900 miles above Earth’s Surface 12 hour Rotation 4 Satellites visible at a 15° angle anytime

6. Farm of the Future Control Segment The control segment tracks the GPS satellites, updates their orbiting position and calibrates and synchronizes their clocks.

7. Farm of the Future User Segment Anyone with a GPS Receiver You in about 15 minutes!!

8. Farm of the Future How Does GPS Work? Satellites send information on their location and the time the code signal was sent. This code allows the GPS receiver to determine its distance to the satellite.

9. Farm of the Future Distance to Satellite Distance = Velocity x Time oSpeed of Light = 186,000 mi/sec oSong Analogy oPseudo Random Code

10. Farm of the Future 2-D Location Locations are found by trilateration oi.e. distances from the satellites oTriangulation implies angle measurement

11. Farm of the Future 3-D Location Requires 4 Satellites Elevation Latitude Longitude Time

12. Farm of the Future GPS Satellite Singnal GPS satellite’s transmit two radio signals L1 and L2

13. Farm of the Future L1 1575.42 MHz Two codes Course Acqusition (C/A) and Precision (P)

14. Farm of the Future L2 1227.6 MHz P code only (a.k.a Y-code) Encrypted Anti-spoofing

15. Farm of the Future Error Sources Sources of Error that Degrade GPS Position: oIonospheric and Atmospheric Delay oSatellite and Receiver Clock Errors oMultipath oDilution of Precision oSelective Availability/Anti-Spoofing

16. Farm of the Future Ionospheric and Atmospheric Delays Signal slows down Satellite Elevation Density of Ionosphere Affected by Sun

17. Farm of the Future Satellite and Receiver Clock Errors Time Drift from Satellite Inaccurate Receiver Clock

18. Farm of the Future Multipath Errors Reflected Satellite Signal oWater oBuildings

19. Farm of the Future Dilution of Precision (DOP) Measure of the strength of satellite geometry oVDOP – Vertical Dilution of Precision oHDOP – Horizontal Dilution of Precision oPDOP – Positional Dilution of Precision oGDOP – Geometric Dilution of Precision

20. Farm of the Future Selective Availabilty/Anti-Spoofing Selective Availabilty (S/A) oDenies Civilians full accuracy of GPS oDithering with Time oEphemeris not real oTurned Off Anti-Spoofing (A-S) oDenies Civilians full accuracy of GPS oEncrypts part of the Satellite Code

21. Farm of the Future GPS Methods There are several different methods of obtaining a position using GPS. The method used depends on the accuracy required by the user. Accurate oHiker or Soldier = Yards oShip or Sprayer = Feet oSurveyor or Lister = Inch

22. Farm of the Future GPS Methods Autonomous Navigation oStand-Alone Receiver oHiker or Soldier oPosition Accuracy = 15-100 yards

23. Farm of the Future GPS Methods Differentially Corrected oAKA DGPS oReceiver and Additional Antennae oShip or Sprayer oPosition Accuracy 1.5-15 feet

24. Farm of the Future GPS Methods Differential Phase Position oAKA- RTK Real-Time Kinematic oPosition Accuracy = <1 inch

25. Farm of the Future Differentially Corrected Positions (DGPS) Many of the errors affecting the measurement of satellite range can be completely eliminated or at least significantly reduced using differential measurement techniques.

26. Farm of the Future DGPS Uses a ground station at a known location Ground station measures error of GPS signal by comparing the known location with the GPS location In real-time, the error transmitted to DGPS unit and position is corrected.

27. Farm of the Future Correction Signal Providers U.S. Coast Guard Local FM Satellite oWAAS oOMNISTAR

28. Farm of the Future Differential Phase GPS Achieves relative position accuracies of typically 0.25-2.5 inches. A lot of Statistics Local ground station sending an FM correction signal.

29. Farm of the Future Accuracy Watch Out For Statistics RMS – Root Mean Square CEP – Circular Error Probable