1. Lecture 11: Global Positioning System (GPS) Lecture 11: Global Positioning System (GPS)

2. Introduction to GPS GPS is funded by and controlled by the US Department of Defense (DOD). GPS provides specially coded satellite signals that can be processed in a GPS receiver, enabling the receiver to compute position, velocity, and time.

3. What is GPS? GPS, which stands for Global Positioning System, is the only system today able to show you your exact position on the Earth anytime, in any weather, anywhere.

4. GPS: Global Positioning System 4

5. GPS components

6. The three parts of GPS are: GPS systems are made up of 3 segments Space Segment (SS) Control Segment (CS) User Segment (US)

7. Space Segment 24 satellites in orbit dedicated to GPS that orbit the Earth in very precise orbits twice a day. 6 satellites are within view of any location at one time. Satellites constantly transmit their location information and time data.

8. Control Segment Ground antennas monitor and track the satellites. They also transmit correction information to individual satellites.

9. Kwajalein Atoll US Space Command Control Segment Hawaii Ascension Is. Diego Garcia Cape Canaveral Ground Antenna Master Control Station Monitor Station

10. User Segment GPS receivers include a display for showing location and speed information to the user.

11. 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

12. Handheld GPS Receivers

13. Casio GPS wristwatch

14. GPS Applications Military: fighters, bombers, detect missiles, weapons, nuclear. Automobiles: show moving maps (highways, buildings) Aviation: for aircraft navigation Marine: Provides precise navigation information to boaters.

16. How GPS works GPS uses satellites as reference points to calculate accurate positions. Each satellite orbits the earth every 12 hours (2 complete rotations every day). This ensures that every point on the Earth will always be in radio contact with at least 4 satellites. Ground stations are used to precisely track each satellite's orbit.

17. How GPS works GPS satellites transmit signals to equipment on the ground. GPS receivers passively receive satellite signals; they do not transmit. GPS operations depend on a very accurate time reference, which is provided by atomic clocks. Each GPS satellite has atomic clocks on board. Each GPS satellite transmits signals that indicates its location and the current time. The signals, moving at the speed of light, arrive at a GPS receiver at slightly different times because some satellites are farther away than others.

18. How GPS works The distance to the GPS satellites can be determined by estimating the amount of time it takes for their signals to reach the receiver. When the GPS receiver estimates the distance to at least four GPS satellites, it can calculate its position (in terms of latitude and longitude). It also can tell you What direction you are heading How fast you are going Your altitude A map to help you arrive at a destination

19. How GPS works GPS also can tell you How far you have traveled How long you have been traveling Estimated time of arrival

20. Calculating Distance Velocity x Time = Distance Radio waves travel at the speed of light, roughly 186,000 miles per second (mps) If it took 0.06 seconds to receive a signal transmitted by a satellite floating directly overhead, use this formula to find your distance from the satellite. 186,000 mps x 0.06 seconds = 11,160 miles

21. Latitude and Longitude Latitude and Longitude are spherical coordinates on the surface of the earth. Latitude is measured North or South of the Equator. Longitude is measured East or West of Greenwich. GPS uses Latitudes and Longitudes to reference locations.

22. Aircraft Navigation using GPS Civil aircraft typically fly from one waypoint to another. With GPS, an aircraft's computers can be programmed to fly a direct route to a destination. This can save fuel and time GPS also can simplify and improve the method of guiding planes to a safe landing, especially in poor weather. With advanced GPS systems, airplanes can be guided to touchdown even when visibility is poor.

23. Waypoints Waypoints are locations or landmarks that can be stored in your GPS. Waypoints may be entered directly by taking a reading with the unit at the location itself, giving it a name, and then saving the point. Once entered and saved, a waypoint remains unchanged in the receiver’s memory until edited or deleted.

24. Waypoints Latitude and Longitude Your location Direction of waypoint Date and Time Waypoint

25. Using GPS, aircraft can fly the most direct routes between airports

26. A GPS receiver in the cockpit provides the pilot with accurate position data and helps him keep the airplane on course.

27. Advantages of GPS in Aviation GPS can provide accurate, continuous, all- weather coverage for aircraft position determination anywhere on the earth. Thus, GPS can serve better air traffic management (ATM) system. GPS can maintain high levels of flight safety GPS can reduce the aircraft delays problem GPS can increase airway capacity. GPS can reduce fuel consumption

28. Advantages of GPS in Aviation Reduced costs to each individual State while increasing overall benefits to individual States Maintain economies from reduced maintenance and operation of ground-based systems (such as VOR/DME/NDB station) Improved ground and cockpit situational awareness Increased landing capacity for aircraft More efficient, optimized, flexible, and user- preferred route structures

29. Time Difference

30. GPS Distance D = Speed of Light x Time; or D = CT D

31. GPS Limitations Line of Sight Transmissions: Obstructions such as trees, buildings may prevent clear line of sight. Refraction: GPS signal from the satellite doesn’t follow a straight line Signal Interference: Sometimes the signals interfered before they hit the receivers.

32. Obstruction

33. Sources of Signal Interference Earth’s Atmosphere Solid Structures Metal Electro-magnetic Fields

34. GPS Frequencies L1 (1575.42 MHz) - For Civilian L2 (1227.60 MHz) - For Civilian L3 (1381.05 MHz) – For Military L4 (1379.913 MHz) – For Research L5 (1176.45 MHz) – For Civilian

35. Local Area Augmentation System (LAAS) “LAAS is a precision approach and landing system that relies on the Global Positioning System (GPS) to broadcast highly accurate information to aircraft on the final phases of a flight. “LAAS is a precision approach and landing system that relies on the Global Positioning System (GPS) to broadcast highly accurate information to aircraft on the final phases of a flight. LAAS support precision approaches and landing capability to aircraft operating within a 20- to 30- mile radius of the airport. LAAS support precision approaches and landing capability to aircraft operating within a 20- to 30- mile radius of the airport. LAAS approaches will be designed to avoid obstacles, restricted airspace, noise-sensitive areas, or congested airspace.” LAAS approaches will be designed to avoid obstacles, restricted airspace, noise-sensitive areas, or congested airspace.”

36. GPS Local Area Augmentation System (LAAS) One LAAS covers multiple runway ends One LAAS covers multiple runway ends LAAS

37. Question The latest addition to navigational aid system is GPS. The latest addition to navigational aid system is GPS. Explain briefly how GPS works. Explain briefly how GPS works. Describe the advantages GPS has over the other navigational aids such as VOR/DME or NDB. Describe the advantages GPS has over the other navigational aids such as VOR/DME or NDB.