GNSS (Global Navigation Satellite System)

Question 1

How do GNSS systems work?

Answer 1

• All GNSS systems work upon the principle of wave propagation and accurate timing.
• The GNSS systems can measure the distance from the satellites and use this to plot position lines, when using multiple satellites an exact position can be calculated.

Question 2

What is GPS?

Answer 2

GPS (Global Positioning System): Uses 24 Satellites (21 Active and 3 Spares), works on 1575.42MHz, an accuracy of 5m.

Question 3

What is GLONASS?

Answer 3

• (Russian) 24 satellites all transmitting on their frequency, but all transmit the same code.
• Accuracy of 5m-10m commercial.

Question 4

What is GALILEO?

Answer 4

GALILEO is currently operational with 22 satellites, with 4 additional ones in the commissioning process. 3 main operational uses:
* Open navigation (1m).
* Encrypted navigation(1cm) .
* Search and rescue capability (EPIRB).

Question 5

What is BEIDOU?

Answer 5

Chinese variant to GALILEO, 44 satellites in orbit, 10m accuracy in general navigation and 10cm for encrypted navigation.

Question 6

What is DGPS?

Answer 6

This is a receiver which automatically applies corrections to raw GPS signals determined and transmitted terrestrial-monitoring stations. Position accuracy reduced to 1-2m.
(To check the accuracy of position Dilution of Position (DOP) should be checked).

Question 7

What are the errors of GPS?

Answer 7

 Horizontal Dilution of Precision (HDoP), caused by satellites directly above your azimuth giving a poor angle of cut.
 Clock errors caused by timings and satellite errors.
 Atmospheric errors caused by satellites low on the horizon or storms.
 Multipath error, bouncing off of other objects taking longer to receive.