Introduction to global position system

Introduction to global position system

1. Introduction to Global Position System

2. Slide 2 What is GPS Space Segment Control Segment User Segment The Global Positioning System (GPS) is a Constellation of Earth-Orbiting Satellites Maintained by the United States Government for the Purpose of Defining Geographic Positions On and Above the Surface of the Earth. It consists of Three Segments:

3. The GPS Constellation

4. Control Segment Space Segment User Segment Three Segments of the GPS Monitor Stations Ground Antennas Master Station

5. GPS Satellite Vehicle Four atomic clocks Three nickel-cadmium batteries Two solar panels Battery charging Power generation 1136 watts S band antenna—satellite control 12 element L band antenna—user communication Block IIF satellite vehicle (fourth generation)

6. Slide 6 Space Segment Description Very high orbit 20,200 km 1 revolution in approximately 12 hrs For accuracy Survivability Coverage 24+ satellites 6 planes with 55° Inclination Each plane has 4 or 5 satellites Broadcasting position and time information on 2 frequencies Constellation has Spares

7. Slide 7 Control Segment Master Control Station Monitor Station Ground Antenna Colorado Springs Hawaii Ascension Islands Diego Garcia Kwajalein Monitor and Control

8. Slide 8 Control Segment (5) Monitor Stations Correct Orbit and clock errors Create new navigation message Observe ephemeris and clock Falcon AFB Upload Station

9. Slide 9 User Segment Over $19 Billion invested by DoD Dual Use System Since 1985 (civil & military) Civilian community was quick to take advantage of the system Hundreds of receivers on the market 3 billion in sales, double in 2 years 95% of current users DoD / DoT Executive Board sets GPS policy PLGR

10. Military. Search and rescue. Disaster relief . Surveying. Marine, aeronautical and terrestrial navigation. Remote controlled vehicle and robot guidance. Satellite positioning and tracking. Shipping. Geographic Information Systems (GIS). Recreation. User Segment

11. ESSC 541-542 Lecture 4.14.05 11 How the system works Space Segment 24+ Satellites The Current Ephemeris is Transmitted to Users Monitor Stations Diego Garcia Ascension Island Kwajalein Hawaii Colorado Springs GPS Control Colorado Springs End User

12. Slide 12 Distance Measuring The whole system revolves around time!!! Distance = Rate x Time Rate = 186,000 miles per second (Speed of Light) Time = time it takes signal to travel from the SV to GPS receiver

13. Signal From One Satellite The receiver is somewhere on this sphere.

14. Signals From Two Satellites

15. Three Satellites (2D Positioning)

16. Three Dimensional (3D) Positioning

17. Slide 17 Triangulation Satellite 1 Satellite 2 Satellite 3 Satellite 4

18. Slide 18 Measuring Travel Time SV Clocks 2 Cesium & 2 Rubidium in each SV $100,000-$500,000 each Receiver Clocks Clocks similar to quartz watch Always an error between satellite and receiver clocks (  t) Require 4 satellites to solve for x, y, z, and  t

19. Slide 19 Common Problems - Errors Direct Signal Reflected Signal GPS Antenna Reflected Signal Hard Surface Satellite

20. Slide 20 GPS Multipath Errors Effects of Multipath on the GPS Signal Avoid Reflective Surfaces Use A Ground Plane Antenna Use Multipath Rejection Receiver Direct Signal Reflected Signal GPS Antenna Reflected Signal Hard Surface Satellite