introduction to global position system
TRANSCRIPT
Introduction to Global Position System
Slide 2
What is GPS
Space Segment
Control Segment
User Segment
The Global Positioning System (GPS) is a Constellation of Earth-Orbiting Satellites Maintained by the United States Government for the Purpose of Defining Geographic Positions On and Above the Surface of the Earth. It consists of Three Segments:
The GPS Constellation
Control Segment
Space Segment
User Segment
Three Segments of the GPS
Monitor Stations
GroundAntennas
Master Station
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)
Slide 6
Space Segment Description
Very high orbit 20,200 km
– 1 revolution in approximately 12 hrs
For accuracy
Survivability
Coverage
24+ satellites 6 planes with 55°
Inclination
Each plane has 4 or 5 satellites
Broadcasting position and time information on 2 frequencies
Constellation has Spares
Slide 7
Control Segment
Master Control Station
Monitor Station
Ground Antenna
ColoradoSprings
Hawaii AscensionIslands
DiegoGarcia
Kwajalein
Monitor and Control
Slide 8
Control Segment
(5) Monitor Stations
• Correct Orbitand clockerrors• Create new navigation message
• Observeephemerisand clock
Falcon AFBUpload Station
Slide 9
User Segment
Over $19 Billion invested by DoD
Dual Use System Since 1985
(civil & military)
Civilian community was quick to take advantage of the system Hundreds of receivers on the market
3 billion in sales, double in 2 years
95% of current users
DoD/DoT Executive Board sets GPS policy
PLGR
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.
User Segment
ESSC 541-542 Lecture 4.14.0511
How the system works
Space Segment24+ Satellites
The Current Ephemeris is Transmitted to Users
Monitor StationsDiego GarciaAscension IslandKwajalein HawaiiColorado Springs
GPS Control Colorado Springs
End User
Slide 12
Distance Measuring
The whole system revolves around time!!!Distance = Rate x Time
• Rate = 186,000 miles per second (Speed of Light)• Time = time it takes signal to travel from the SV to GPS receiver
Signal From One Satellite
The receiver is somewhere on this sphere.
Signals From Two Satellites
Three Satellites (2D Positioning)
Three Dimensional (3D) Positioning
Slide 17
Triangulation
Satellite 1 Satellite 2
Satellite 3 Satellite 4
Slide 18
Measuring Travel Time
SV Clocks 2 Cesium & 2 Rubidium in
each SV $100,000-$500,000 eachReceiver Clocks Clocks similar to quartz watch Always an error between satellite and receiver clocks ( t) Require 4 satellites to solve for x, y, z, and t
Slide 19
Common Problems - Errors
GPSAntenna
Hard Surface
Satellite
Slide 20
GPS Multipath Errors
Effects of Multipath on the GPS Signal
•Avoid Reflective Surfaces•Use A Ground Plane Antenna •Use Multipath Rejection Receiver
GPSAntenna
Hard Surface
Satellite