INS & GPS

Question 1

What is a GNSS and how does it operate?

Answer 1

A collection of satellites that know their location, time, and encode messages with this information for transmission to users.
Master control station is the hub of all information and uses monitor stations and ground antennas to collect information and instruct satellites what to do.

Question 2

Main sources of error in GPS calculations.

Answer 2

Satellite time differs from user time.
Relativistic effects due to speed and gravity (38micro s).
Ephemeris error (12hr check, 2.5m Max)
Satellite clock error (12hr check, 1.5m Max)
Ionospheric propagation error (5m Max)
Tropospheric propagation error (0.5m Max)
Noise error (0.3m Max)
Multi-path error (0.6m Max)

Question 3

INS?

GNSS?

Answer 3

Inertial Navigation Systems

Global Navigation Satellite Systems

Question 4

What is an INS?

Answer 4

Measures altitude rates and translational acceleration.
- combines these to calculate inertial velocity which is integrated to find position.

Must be corrected for wander and kept level, relative to local earth axes.

2 types: stabilised and strap down

Question 5

Earth centred

Earth fixed

Answer 5

z,y,x

n,e,d