Seminar ppt on GPS

1. The Global Positioning
System an Overview
Presented by
Gurubasavaraj M
AIET Moodbidri
Dept of Civil Engg
USN 4al14cv403

2. Contents
1. What is GPS ?
2. Segments of GPS
3. Satellite Constellation
4. GPS Signals
5. GPS: How does it work?
6. Sources of GPS Error
7. Characteristics of GPS
8. Applications of GPS
9. Conclusion
10. Reference

3. What is GPS?
A very precise positioning system
•Developed and maintained by the US Department
of Defense (DOD)
• Satellite Based
* 24 satellites in 6 orbital planes
* 4 satellites in each plane
* 20,200 km high orbit
* 55 Degree inclination
Although it is a very precise geographic positioning system.
•It is very easy to get yourself into trouble
•Why?
•Because you (probably) don’t understand how it works
•And that leads to garbage

4. GPS Segments
GPS has 3 Segments:
1. Space Segment : the constellation of satellites
2. Control Segment : control the satellites
3. User Segment : users with receivers

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

6. 1.Space Segment
• System consists of 24 satellites
in the operational mode: 21 in
use and 3 spares 3 other
satellites are used for testing
• Altitude: 20,200 Km with
periods of 12 hr.
• Current Satellites: Block IIR-
$25,000,000
2000 KG
• Hydrogen Maser Atomic
Clocks:
These clocks lose one
second every 2,739,000 million
years.

7. 2.Control Segment
• The control segment tracks the satellites and then provides
them with corrected orbital and time information.
• The control segment consists of four unmanned control
stations and one master control station.
• The four unmanned stations receive data from the satellites
and then send that information to the master control station
where it is corrected and sent back to the GPS satellites.

8. Kwajalein Atoll
US Space Command
Control Segment
Hawai
i
Ascension Is.
Diego Garcia
Cape Canaveral
Ground AntennaMaster Control Station Monitor Station

9. 3.User Segment
• 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.

10. • GPS Nominal Constellation
• 24 Satellites in 6 Orbital Planes
• The nominal orbital period of a
GPS satellite is one-half of a
sidereal day or 12hr.
• 4 Satellites in each Plane
• 20,200 km Altitudes, 55 Degree
Inclination.
• The orbital radius is
approximately 26 600 km.
Satellite Constellation

11. GPS Signals
• Two signals are transmitted on carriers:
L1 = 1575.42 MHz
L2 = 1227.60 MHz
These are derived from the system clock of 10.23 MHz (phase quadrature)
• Modulation used is Direct Sequence Spread Spectrum
(code division multiple access - CDMA)
• The satellites transmit as part of their unique Spread Spectrum signal a
clock or timing signal.
• The range or distance to the satellite is obtained by measuring how long it
takes for the transmitted signal to reach the receiver.
• This is not the “true” range due to clock errors - what is obtained is know as
the “pseudo-range.

13. GPS: How does it work?
1. All satellites have clock set to exactly to the same time.
2. All satellites know their exact position from data sent to them from
the system controllers.
3. Each satellite transmits its position and a time signal.
4. The signals travel to the receiver delayed by distance travelled.
5. The differences in distance travelled make each satellite appear to
have a different time.
6. The receiver calculates the distance to each satellite and can then
calculate its own position.

14. Working of GPS System

15. Sources of GPS Error
Standard Positioning Service (SPS ): Civilian Users
Source Amount of Error
• Satellite clocks: 1.5 to 3.6 meters
• Orbital errors: < 1 meter
• Ionosphere: 5.0 to 7.0 meters
• Troposphere: 0.5 to 0.7 meters
• Receiver noise: 0.3 to 1.5 meters
• Multipath: 0.6 to 1.2 meters
• User error: Up to a kilometer or more
Errors are cumulative and increased by PDOP.

16. Characteristics of GPS
• Free
• Precise
• Reliable
• All weather
• Anytime & anywhere
• Anytime & anywhere
• Unlimited user capacity

17. Applications of GPS
The following is the list of some application areas where
GPS has been used widely.
• Utility industry
• Natural resources
• Precision farming
• Civil Engineering applications
• Structural deformations
• Airborne mapping
• Seafloor mapping
• Land & marine seismic surveying
• Vehicle navigation
• Cadastral surveying

18. Conclusion
• GPS system is actually developed for military purpose
but by finding its enormous use this has been made
available for civilian purposes.
• GPS service is offered by US Department of
defense(DOD) called NAVSTAR GPS.
• NAVSTAR (Navigation Satellite and Time Ranging) GPS
is used widely.
• Russia has a system known as GLONASS or “GLObal
Navigation Satellite System” .
• European Union(EU) has also planned its GPSmission
called Galelio.

19. Reference
• A text book of SURVEYING III by H.S.Vishwanath.
• Wikipedia
Websites
• www.google.com/GPS
• GPS World Magazine
http://www.gpsworld.com/

20. Thank you…,