Introduction to Global Positioning Systems (GPS)

1. Introduction to Global Positioning Systems (GPS) Mark Smith, Assistant Professor/Wildlife Extension Specialist

2. GPS Basics • Satellite navigation system • Maintained by the US Government • All weather • 24 hour • Worldwide • Available free to the public

3. Global Position “System” • Space segment • 24 satellites emitting radio signals • Control Segment • US DOD • User Segment • Your receiver

4. GPS Basics • Radio signals sent from orbiting satellites to earth • Measures receiver-to-satellite distance • How long the signal took to get to your receiver • Speed of light (186,000 m/s) • Atomic clocks • GPS units receive and convert signals to position, velocity, and time information

5. GPS Basics • What’s in a radio signal? • Psuedorandom code – identifies the satellite • Ephemeris data – tells where the satellite should be • Almanac data – tells the health of the satellite • Constellation of 24 NAVSTAR earth-orbiting satellites • Need to receive a signal from: • 3 satellites for a 2D position • 4 satellites for a 3D position

6. Sources of GPS Error • Satellite availability • Satellite geometry • Ionosphere/troposphere conditions • Signal blockage (i.e., forest canopy, tall buildings) • Multi-path (signal bounce) • Clock error (timing) • Intentional degradation (the old Selective Availability)

7. Overcoming some forms of GPS error • Differential correction • Real time • Post-processing • “Base” station at a known location recording satellite signals simultaneously • Differences in timing are then applied to the signals you recorded with your receiver • WAAS enable units • Wide Area Augmentation System • Modified GPS signal---with error correction factor • North America only • 25 ground reference stations that collect signals and then send correction info to satellites which gets sent to your receiver

9. Measures of Position Accuracry • DOP – Dilution of Precision • Indicator of the quality of the satellite constellation • Lower is better • Types of DOP • PDOP – Position Dilution of Precision • VDOP – Vertical Dilution of Precision • HDOP – Horizontal Dilution of Precision

10. Coordinate Systems • Latitude/Longitude • Degrees, minutes, seconds (33o 14’ 32”) • Decimal degrees (33.242222o) • Projections • How “3D” objects are converted to “2D” objects • Cylindrical, Conical, and Planar • Datums • How the earth is shaped • Based on mathematical models of the earth’s shape and dimensions • Universal Transverse Mercator (UTM) • Cylindrical • 60 6-degree slices • Meters • Example: UTM, Zone 16N, NAD-27

11. UTM Zones

12. Which GPS Receiver is Best? • Deluxe • Survey grade units • Used for highway and engineering projects • Horizontal accuracy within a centimeter • Costs up to $40,000 • Mapping/resource grade units • Used for mapping roads, stand boundaries, and point data • Relocating data that is not flagged or marked • 1-5 meter accuracy with good signal • Usually requires formal training to use • Download data to Geographic Information System • Costs begin around $2,000

13. Which GPS Receiver is Best? • Economical • Recreational grade units • General navigation • Relocating plots, trees, etc. that have been flagged • Estimating acreage of forest stands • 3-5 meter accuracy with good signal • Easy to learn using manual • Costs $100 - $500

14. Which GPS Receiver is Best? • Grade GPS you choose depends on field work and data collection needs • Recreational grade – most forest inventory tasks • Resource/mapping grade- determining harvest boundaries • Recreational grade are good for first-time GPS users

15. GPS in Forestry • Navigation • Pre-harvest and post-harvest stand delineation • Road and landing layout • Acre control • Equipment tracking • Wildlife uses

16. Stand Delineation • Estimating acreages • Tree planting • Herbicide application • Slope/aspect

17. 155 gm 760 gm 350 gm 1,100 gm Wildlife • GPS collars • Large mammals • Waterfowl

18. Questions/Discussion