Fundamental of GPS

1. Introduction to the
Global Positioning System
S.M.J.S.Samarasinghe
Superintendent of Surveys
Institute of Surveying and Mapping
Diyatalawa - Sri Lanka.

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

3. History of the GPS
 1969—Defense Navigation Satellite
System (DNSS) formed
 1973—NAVSTAR Global Positioning
System developed
 1978—first 4 satellites
launched
Delta rocket launch

4. History of the GPS
 1993—24th satellite
launched; initial
operational capability
 1995—full operational
capability
 May 2000—Military
accuracy available to
all users

5. Components of the System

6. GPS Communication and Control

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

8. The GPS Constellation
Space segment

9. 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)
Space segment

10. GPS Satellite Vehicle
 Weight
 2370 pounds
 Height
 16.25 feet
 Width
 38.025 feet including
wing span
 Design life—10 years
Block IIR satellite vehicle
assembly at Lockheed
Martin, Valley Forge, PA
Space segment

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

12. Components of the System
User segment

13. How does GPS work?
Pseudo-Random Code
 Complex signal
 Unique to each
satellite
 All satellites use
same frequency
 “Amplified” by
information theory
 Economical

14. Handheld GPS Receivers
 Garmin eTrex
 ~$100
 Garmin-12
 ~$150
 Casio GPS
wristwatch
 ~$300
 The GPS Store

15. GPS Operation Jargon
 “Waypoint” or “Landmark”
 “Track” or “Heading” (Heading is
the direction in which you are currently
moving)
 “Bearing”
 CDI(The Course Deviation Indicator, CDI, is key
to maintaining your position as you traverse from
one waypoint to another in water or air)
 Route
 Mark
 GOTO
GPS/Digital Telephone

16. GPS Operation Jargon
“Waypoint”

17. GPS Operation Jargon
Route

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

19. GPS Ground Control Stations
Ground control segment

20. GPS Ground Control Stations
Ground control segment

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

22. How does GPS work?
 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.
 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.
 High-tech simulation

23. How does GPS work?
 Accurate timing is the key to measuring
distance to satellites.
 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.

24. How does GPS work?
 To use the satellites as references for range
measurements we need to know exactly where they are.
 GPS satellites 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.
 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.

25. GPS Position Determination

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

27. System Performance
Selective availability
 Intentional degradation of signal
 Controls availability of system’s full capabilities
 Set to zero May 2000
 Reasons
 Enhanced 911 service
 Car navigation
 Adoption of GPS time standard
 Recreation

28. System Performance
 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.
 The configuration of the satellites in the
sky can magnify other errors.
 Differential GPS can reduce errors.

29. System Performance

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

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

32. Positioning

33. Dam /Hydro Power Monitoring

34. Victoria Dam Monitoring
Beacon 8
Beacon 5

35. Vehicle Monitoring System

36. Eagles Eye

38. Surveying

39. Precise Positioning

42. GPS Navigation

43. Tracking

44. Tracking

45. Tracking

46. Environmental Monitoring

47. Global Navigation Satellite
Systems (GNSS)

48. Global Navigation Satellite
Systems (GNSS)

49. GPS News
 http://www.gpseducationresource.com/gps
news.htm
 One–page reading exercise
 Center of page—main topic
 Four corners—questions & answers from
reading
 Four sides—specific facts from reading
 Spaces between—supporting ideas,
diagrams, definitions
 Article citation on back of page

50. Military Uses for the GPS
Operation Desert Storm
 Featureless terrain
 Initial purchase of 1000 portable commercial
receivers
 More than 9000 receivers in use by end of the
conflict
 Foot soldiers
 Vehicles
 Aircraft
 Marine vessels

51. GPS for Gunners

52. On Target

53. Attached to

54. GPS Guided Artillery Shell

55. JDAM

56. Precision Guided Air Drop
the Marine Corps has been utilizing a
different style of parachute than the
traditional round system used to
airdrop heavy packages. This new
parachute system, the Sherpa, has the
ability to guide itself to the drop zone
from up to 25,000 feet in the air and
15 miles away, landing within 100
yards of the targeted point of impact
while carrying up to 2,200 pounds of
supplies.

57. Equipped with a 1,200-square-foot canopy, the Sherpa is
programmed with the information of where it needs to go, as well as
how long after it falls from the aircraft before it opens the
parachute. After it is programmed, the GPS-guided parachute
attached to its cargo is loaded aboard an aircraft, flown close to the
drop zone and tossed from the plane to make the rest of the way on
its own.
The main canopy steering lines are connected to the control lines in
the airborne guidance unit, which operates with two servo
motors.The motors turn to 'reel in' the control lines, allowing for the
parachute to turn. The turns are determined by the mission that is
programmed into it and based on winds and the target point. The
GPS allows for the system to know where it is in the sky and then
determine how it needs to get to where it is going."

59. GPS Guided Mobility

60. GPS Guided Mobility

61. Geocaching
 Cache(Cell) of goodies
established by individuals
 Coordinates published on
Web
 Find cache
 Leave a message
 Leave some treasure(Ex Gem)
 Take some treasure
 http://www.geocaching.com/

62. GPS Websites
 USNO NAVSTAR Homepage
 Info on the GPS constellation
 How Stuff Works GPS
 Good everyday language explanation
 Trimble GPS tutorial
 Flash animations
 GPS Waypoint registry
 Database of coordinates

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

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

65. Thanks for your interest in the Global
Positioning System