GPS Flashcards
GNSS Stand for?
Global navigation satellite systems
What is the principle behind GPS position fixing?
Using 3 satellites giving 3 lines required for a 3D fix.
4th satellite required for time.
What does GPS provide?
Provides a mean of navigation by satellites which relies on accurate time info to determine ranges
Name the 3 main components to the gps system.
1- control segment
2- space segment
3- user segment
What’s NAVSTAR GPS stand for?
Navigation satellites with time and ranging Global Positioning System.
What are the control segments and where would you find some?
-Find some along the equator.
-They monitor position of satellites and time of clocks.
-can form nav messages which uploaded every 8 hours.
What happens if a control system was every disabled?
Then pre stored messages are available in each satellite.
14 day prediction.
After this the accuracy exceeds 400m therefore no longer suitable for nav.
What does the space segment consist of?
-24 satellites, 20,200km high. X3 clocks
Each satellite transmits data on 2 frequencies. (Coded) contains the satellite positions.
What’s the user segment?
Is the operator and receiver (me using it)
1575 mHzt
1227 mHzt
What is HDOP?
Horizontal dilution of position. It’s the value displayed on the GPS.
Best DOP value is 1. Gives an indication to quality of position info.
Which MGN is GPS
MGN 138
Name the sources of error:
1- multi path error (mountains, buildings, etc reflecting signals causing unit to receive more than 1. =errors up to 0.6m
2- ionosphere error (layer in atmosphere, can slow passage of gps signal)
3- satellite clock error
4- tropospheric delay (weather, temp, pressure etc)
5- receiver noise
What’s the datum for GPS?
WGS84
