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?
- The distance between a satellite and a navigation satellite receiver
- Includes a time value error within, so the ranges are not accurate
Explain how the range from a satellite is determined?
- The Satelite transmits a distinct code
- At the same time the receiver generates the code from the satellite
- The receiver receives the code from the satelite
- Time difference between the two codes is meassured
- The range from the satellite is calculated by using the speed triangle
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
- 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 Control segment
- 2nd segment of GPS
- master control in colarado
- 5 monitoring staions around the earth
- all located close to equator
Define the Space segment
1st segment of GPS -
- minimum of 24 satellites for ops
- 6 orbital planes
- cirlces the earth every 12 hours
