GPS Flashcards
- In the operation of a Global Navigation Satellite System what are the three distinct parts (In GPS
known as segments)
Space Segment
Control Segment
User Segment
- What is the minimum number of satellites that GPS is designed to operate with?
24
receiver gives the user a position by calculating its ranges from satellites, these are called pseudo ranges, why?
- Includes a time value error within, so the ranges are not accurate
Explain how the range from a satellite is determined?
- The satellite transmits a distinct code
- At the same time the receiver generates the code
- The receiver receives the code from the satellite
- The time difference between the two codes is measured
- The range from the satellite is calculated using the speed triangle,
- Where S is the speed of the electromagnetic wave
List 4 errors which can affect range measurement? (GPS)
Any of these six:
1. Ionospheric delay error
2. Tropospheric delay error
3. orbit error
4. Multipath error
5. Clock error
6. Receiver error
What must the OOW do when plotting a satellite position on a chart?
Check whether satellite positions can be plotted directly on the chart
If not, then check the note that states the corrections must be applied
Correct the satellite position
Plot corrected position on the chart
State GPS datum and describe what is meant by datum in this context
reference point
WGS84 is the horizontal datum for GPS
Define DOP
Dilution of Precision: The reliability of the data due to the position of satellites in view of the receiver.
State one example of a good DOP value and one example of a poor DOP value
Good: 2 Poor: 8
Which type of DOP is the OOW most interested in?
HDOP – Horizontal Dilution of Precision
What does the ‘D’ stand for in DGPS and what two augmentation systems are there?
Differential
(GBAS) Ground based Augmentation System
(SBAS) Satellite based Augmentation System
Explain how DGPS improves the accuracy of GPS
GPS monitoring station knows its own WGS84 location
Compares position with GPS derived position
Any difference in its known position and position received can be calculated
Explain, with the aid of a diagram, why a cross-track error alarm should be set when following a GPS route
- If the vessel is off track there could be an obstruction between the vessel and the waypoint.
- Therefore an alarm should be set to alert the user.
Define the Ground segment
- 1st segment of GPS
- master control in colarado
- 5 monitoring staions around the earth
- all located close to equator
Define the Space segment
- 2nd segment of GPS
- minimum of 24 satellitesfor ops
- 6 orbital planes
- min of 4 satelites
