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Introduction to the Global Positioning System. What is the GPS? Orbiting navigational satellites Orbiting navigational satellites Transmit position and.

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Presentation on theme: "Introduction to the Global Positioning System. What is the GPS? Orbiting navigational satellites Orbiting navigational satellites Transmit position and."— Presentation transcript:

1 Introduction to the Global Positioning System

2 What is the GPS? Orbiting navigational satellites Orbiting navigational satellites Transmit position and time data Transmit position and time data Handheld receivers calculate Handheld receivers calculate latitude latitude longitude longitude altitude altitude velocity velocity Developed by Department of Defense Developed by Department of Defense

3 Components of the System Space segment 24 satellite vehicles 24 satellite vehicles Six orbital planes Six orbital planes Inclined 55 o with respect to equator Inclined 55 o with respect to equator Orbits separated by 60 o Orbits separated by 60 o 20,200 km elevation above Earth 20,200 km elevation above Earth Orbital period of 11 hr 55 min Orbital period of 11 hr 55 min Five to eight satellites visible from any point on Earth Five to eight satellites visible from any point on Earth Block I Satellite Vehicle

4 The GPS Constellation

5 GPS Satellite Vehicle Weight Weight 2370 pounds 2370 pounds Height Height feet feet Width Width feet including wing span feet including wing span Design life10 years Design life10 years Block IIR satellite vehicle assembly at Lockheed Martin, Valley Forge, PA

6 Components of the System User segment GPS antennas & receiver/processors GPS antennas & receiver/processors Position Position Velocity Velocity Precise timing Precise timing Used by Used by Aircraft Aircraft Ground vehicles Ground vehicles Ships Ships Individuals Individuals

7 Components of the System Ground control segment Master control station Master control station Schreiver AFB, Colorado Schreiver AFB, Colorado Five monitor stations Five monitor stations Three ground antennas Three ground antennas Backup control system Backup control system

8 GPS Communication and Control

9 How does GPS work? Satellite ranging Satellite ranging Satellite locations Satellite locations Satellite to user distance Satellite to user distance Need four satellites to determine position Need four satellites to determine position Distance measurement Distance measurement Radio signal traveling at speed of light Radio signal traveling at speed of light Measure time from satellite to user Measure time from satellite to user Low-tech simulation Low-tech simulation

10 How does GPS work? Distance to a satellite is determined by measuring how long a radio signal takes to reach us from that satellite. Distance to a satellite is determined by measuring how long a radio signal takes to reach us from that satellite. To make the measurement we assume that both the satellite and our receiver are generating the same pseudo-random codes at exactly the same time. To make the measurement we assume that both the satellite and our receiver are generating the same pseudo-random codes at exactly the same time. By comparing how late the satellite's pseudo-random code appears compared to our receiver's code, we determine how long it took to reach us. By comparing how late the satellite's pseudo-random code appears compared to our receiver's code, we determine how long it took to reach us. Multiply that travel time by the speed of light and you've got distance. Multiply that travel time by the speed of light and you've got distance. High-tech simulation High-tech simulation High-tech simulation High-tech simulation

11 How does GPS work? Accurate timing is the key to measuring distance to satellites. Accurate timing is the key to measuring distance to satellites. Satellites are accurate because they have four atomic clocks ($100,000 each) on board. Satellites are accurate because they have four atomic clocks ($100,000 each) on board. Receiver clocks don't have to be too accurate because an extra satellite range measurement can remove errors. Receiver clocks don't have to be too accurate because an extra satellite range measurement can remove errors.

12 How does GPS work? To use the satellites as references for range measurements we need to know exactly where they are. To use the satellites as references for range measurements we need to know exactly where they are. GPS satAellites are so high up their orbits are very predictable. GPS satAellites are so high up their orbits are very predictable. All GPS receivers have an almanac programmed into their computers that tells them where in the sky each satellite is, moment by moment. All GPS receivers have an almanac programmed into their computers that tells them where in the sky each satellite is, moment by moment. Minor variations in their orbits are measured by the Department of Defense. Minor variations in their orbits are measured by the Department of Defense. The error information is sent to the satellites, to be transmitted along with the timing signals. The error information is sent to the satellites, to be transmitted along with the timing signals.

13 GPS Position Determination

14 System Performance Standard Positioning System Standard Positioning System 100 meters horizontal accuracy 156 meters vertical accuracy Designed for civilian use No user fee or restrictions Precise Positioning System Precise Positioning System 22 meters horizontal accuracy 27.7 meters vertical accuracy Designed for military use

15 System Performance Selective availability Intentional degradation of signal Intentional degradation of signal Controls availability of systems full capabilities Controls availability of systems full capabilities Set to zero May 2000 Set to zero May 2000 Reasons Reasons Enhanced 911 service Enhanced 911 service Car navigation Car navigation Adoption of GPS time standard Adoption of GPS time standard Recreation Recreation

16 System Performance The earth's ionosphere and atmosphere cause delays in the GPS signal that translate into position errors. The earth's ionosphere and atmosphere cause delays in the GPS signal that translate into position errors. Some errors can be factored out using mathematics and modeling. Some errors can be factored out using mathematics and modeling. The configuration of the satellites in the sky can magnify other errors. The configuration of the satellites in the sky can magnify other errors. Differential GPS can reduce errors. Differential GPS can reduce errors. Differential GPS Differential GPS

17 Application of GPS Technology Location - determining a basic position Location - determining a basic position Navigation - getting from one location to another Navigation - getting from one location to another Tracking - monitoring the movement of people and things Tracking - monitoring the movement of people and things Mapping - creating maps of the world Mapping - creating maps of the world Timing - bringing precise timing to the world Timing - bringing precise timing to the world

18 Application of GPS Technology Private and recreation Private and recreation Traveling by car Traveling by car Hiking, climbing, biking Hiking, climbing, biking Vehicle control Vehicle control Mapping, survey, geology Mapping, survey, geology English Channel Tunnel English Channel Tunnel Agriculture Agriculture Agriculture Aviation Aviation General and commercial General and commercial Spacecraft Spacecraft Maritime Maritime

19 Classroom Applications Physics Physics Distance, velocity, time Distance, velocity, time Orbital concepts Orbital concepts Earth Science Earth Science Mapping Mapping Spacecraft Spacecraft Environmental Science Environmental Science Migratory patterns Migratory patterns Population distributions Population distributions GLOBE Program GLOBE Program GLOBE Program GLOBE Program Mathematics Mathematics Mathematics Geography Geography Geography Technology Technology

20 Classroom Applications Careers Aerospace Aerospace Satellite vehicles Satellite vehicles Launch vehicles Launch vehicles Hardware engineering Hardware engineering Ground control systems Ground control systems User systems User systems Software engineering Software engineering Research careers Research careers

21 Conclusion 1. GPS is finding its place in every corner of our life. Today, we find many applications of GPS all around us. 2. Its like giving every square meter on the planet a unique address. In future, the airplanes with GPSRs will be able to land even in dark and in moist conditions. 3. In no time GPS will be a complete part of our life, just as a mobile we have today.


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