1. Understanding GPS-GNSS Michael Buschermohle Precision Agriculture Specialist UT Extension Michael Buschermohle Precision Agriculture Specialist UT Extension

2. Global Navigation Satellite System (GNSS) Global Positioning System (GPS): 24 Satellites (USA)Global Positioning System (GPS): 24 Satellites (USA) GLONASS : 18 Satellites (Russia)GLONASS : 18 Satellites (Russia) Galileo: 2 Satellites (European Union)Galileo: 2 Satellites (European Union) Compass: ChinaCompass: China QZSS: JapanQZSS: Japan IRNSS: IndiaIRNSS: India Satellite Systems GNSS = GPS + GLONASS + future additional satellite systems

3. Advantages of GNSS Advantages Increased accuracy and reliability due to tracking more satellitesIncreased accuracy and reliability due to tracking more satellites GPS GNSS Need 5 satellites to maintain RTK-fix

4. How Does GPS Work Satellites broadcast several pieces of information Emphemeris (Orbital) data Emphemeris (Orbital) data Timing data Timing data

5. Sources of GPS Error Clock Errors Clock Errors Atmospheric Interference Atmospheric Interference Ephemeris (Orbital) Variation Ephemeris (Orbital) Variation Satellite Configuration Satellite Configuration Signal Multipath Signal Multipath

6. Sources of GPS Error Clock Errors Let’s put some numbers on it Altitude = 12,500mi. Speed of light = 186,000 mi/sec Transmission Time = 0.067 sec What happens if we are off a little? 0.001 sec * 186,000 mi/sec = 186 mi

7. Sources of GPS Error Atmospheric Interference

8. Precision Agriculture University of Tennessee Extension Sources of GPS Error Ephemeris (Orbital) Variation

9. Sources of GPS Error Satellite Configuration Poor (high) DOP Good (low) DOP

10. Signal Multipath Sources of GPS Error

11. Counteracting GPS Errors Land-Based Differential CorrectionLand-Based Differential Correction Satellite-Based Differential CorrectionSatellite-Based Differential Correction Real-Time Kinematic CorrectionReal-Time Kinematic Correction

12. Differential GPS (DGPS) Corrections Satellite-Based Differential GPS Correction WAASOmniStar JD StarFire

13. Differential GPS Corrections ) ) ) ) ) ) ) Real-Time Kinematic (RTK) GPS Correction Base Station Virtual Reference Station Continuous Operating Reference Station (CORS)

14. GPS Accuracy Pass-to-Pass AccuracyPass-to-Pass Accuracy –Represents the short-term (<15 min.) relative accuracy of a GPS/GNSS receiver. You can think of this as the accuracy between adjacent, parallel passes made within 15 minutes of one another. GPS/GNSS Drift - Year-To-Year AccuracyGPS/GNSS Drift - Year-To-Year Accuracy –Drift can be defined as GPS/GNSS receiver (guidance system) accuracy over time. Causes of drift are changes in satellite configuration, operating near trees or other obstacles, and satellite data errors.

15. GPS Accuracy Courtesy of Fulton, Auburn University Correction Service Pass-to-Pass Accuracy Potential Range of Drift WAAS± 6 to 13 inches± 4.7 ft Sub-meter± 6 to 13 inches± 2.3 ft Decimeter± 2 to 4 inches± 1.7 ft RTK± 1 inch

16. Correction ServicePass-to-Pass Accuracy + Potential Range of Drift* WAAS + 6 to 13 inches + 4.7 ft JD StarFire 1 OmniStar XP (Sub-Meter) + 6 to 13 inches + 2.3 ft JD StarFire 2 OmniStar HP (Decimeter) + 2 to 4 inches + 1.7 ft RTK + 1 inch + Based on manufacturer literature * Based on research conducted at Auburn University GPS Accuracy

17. Differential Correction Services Correction ServiceProviderOperating Fee/year WASSFAA No VBS OmniSTAR $800/year XP $1000/year HP $1,500/year StarFire1 John Deere No StarFire2 $800/year RTKTN Tractor $800 - 1200/year RTXTrimble $1000/year VRSMultiple Providers Varies CORS TDOT $300/year Earl Dudley $1000/year

18. GPS Accuracy WASSSub-MeterDecimeterRTK XXXXMapping XXXX Soil Sampling XXXXScouting XXXX Yield Monitoring XXXXLightbars XXXXVRA XX Section Control XAuto-Guidance X Land Leveling

19. Questions