global positioning systems glen t. huettl agricultural education garrison high school
TRANSCRIPT
Global Positioning Systems
Glen T. Huettl
Agricultural Education
Garrison High School
Global Positioning System (GPS)
• Navigation and Positioning System
• Determines Exact Location
• Establishes Longitude, Latitude, Altitude
GPS Components
• Satellites in Space Send Signals
• Receivers on the earth Receive the Signals
• Software Converts Satellite Signals
• Position Monitoring Equipment Validate Satellite Location
How GPS Works
• Receivers calculate position by reading 3 or more satellite signals
• Called “Triangulation”
• Theory used before GPS to locate earthquakes
GPS Developed By:
• U.S. Department of Defense
• Available for both Civilian and Military Uses
• Available 365 days a year
Commerical Applications
• Emergency Vehicles
• Electronic Maps in Cars
• Aircraft Landing Systems
• Delivery Vehicles
• Sea Navigation
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
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
Satellites (cont’d)
• Act as Reference Points
• Position known and precisely measured
• Control Segment continually monitor accuracy of signal
• Atomic Clocks provide timing accuracy
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
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
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”)
Control Segment
• Monitor Satellite Signal for Accuracy
• Located around the world
• Satellites pass over monitors every 12 hours
• Measure signals and correct positional errors
Error Sources
• Selective Availability
• Particles in the Ionosphere
• Atomic Clocks
• Speed of Light Calculations
• Multipath Errors
• Receiver Errors
Error Correction Methods
• Control Segment Error Correction
• Differential Global Positioning System (DGPS)
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
DGPS (cont’d)
• Cancels out natural and man-made errors
• Makes GPS positioning very precise
• Broadens GPS applications because of accuracy of Differential signal.
DGPS Uses
• Coast Guard
• Natural Resource Management
• Forest Service
• Offshore Exploration
• Agricultural Uses
Commercial USES
• Yield Monitors
• Variable Rate Technology
• Field Mapping and Acreage Management
• Noting Underground Locations
WAAS Wide Area Augmentation System
• Government supplied correction
• Approx 25 land based stations