THE GLOBAL POSITIONING SYSTEM (G.P.S.)

Overview Introduction The GPS System (3 components) Calculating a Position Differential GPS

Introduction Introduction NAVSTAR GPS: Navigation Satellite Timing and Ranging Global Positioning System Funded and controlled by the US Department of Defence COMPOSED OF THREE MAIN SEGMENTS Space Segment Control Segment User Segment

Components to the System Constellation of satellites orbiting the earth (NAVSTAR) Ground Control Stations (main one in Colorado Springs) GPS Receivers (The Users)

Components SPACE SEGMENT 24 operational satellites orbiting the earth Arranged so that 4 satellites are placed in each of the six orbital planes 4 to 10 visible anywhere in the world Circle the earth twice a day

Components CONTROL SEGMENT These control stations monitor and control the information being sent by the satellites (time, orbit)

Components USER SEGMENT The user holds the GPS receiver that receives the codes transmitted by the satellites. It must use this information to calculate its position. Read on! Civilian Uses single frequency (L1) 1 code Military Uses two frequencies (L1/L2) 2 codes (determines time)

Calculating a Position Components Calculating a Position SIGNALS Satellites send out signals at different frequencies (L1/L2) Codes are used to transmit time The receiver uses this information to calculate a position through the following steps: Determine distance Position of satellites (orbit/ephemeris) Triangulate

1. Determine Distance DISTANCE = VELOCITY X TIME DELAY Components DISTANCE = VELOCITY X TIME DELAY The signals travel through radio waves, therefore, they travel the speed of light! Velocity = Speed of light (186 000 miles/second) The measured delay between the transmitted code and the received code is the TIME DELAY. Now the receiver can calculate the distance to the satellite. BUT…WHERE are the satellites?

1. Determine Distance Components

2. Position of Satellites Components Where are the satellites in space? Without going into too much detail here… The satellites send information about its: Orbital Path (ephemeris) – indicates its position in its elliptical path around the earth. This is used to determine the position of the satellites exact position relative to the earth (x,y,z) Now the receiver has distance to satellites and position. It needs to triangulate! Read on!

3. Triangulation Components A receiver will need the distance and position of at least three satellites to get an accurate position. Why? D1 D2

3. Triangulation Components A receiver will need the distance and position of at least three satellites to get an accurate position. Why?

3. Triangulation Components A receiver will need the distance and position of at least three satellites to get an accurate position. Why?

3. Triangulation Components A receiver will need the distance and position of at least three satellites to get an accurate position. Why? You’ve found your position! EARTH

Still Confused? Components Check out these webpages and/or downloadables: WEBPAGES: http://www.trimble.com/gps/how.html http://www.garmin.com/aboutGPS/ http://www.magellangps.com/en/products/aboutgps/ DOWNLOADABLE from OUR site: NOVAGPS9.exe – an executable that goes over triangulation garminbeg.pdf – a beginner’s guide to GPS

Research Components From the websites and downloadable PDF document on the following slide, find out the answers to the following: Why do you think a fourth satellite may help in triangulation. What is selective availability? What type of errors are inherent in GPS signals? Name and explain at least four. Explain Differential GPS? (DGPS)? Why would you want it? How does it work? Name and explain three different ways of surveying using GPS. Which one would be most accurate? Why?

Research Components Provide one case study of where GPS is used in Canada. Incorporate a picture. Find an article or two relating to GPS and the war in Iraq. Use this article to explain how the coalition forces (specifically U.S.) is using GPS in the war. Have they encountered any problems? What did they have to think about when they planned a “smart war” with Iraq? Anything else you learned.

Triangulation Components Source of error with three satellites. Four used for more precision.