GNSS Flashcards
What are the 4 system a GNSS includes
- One or more satellite
- Aircraft recievers
- System integrity monitoring
- Augmentation
What type of modeling does GPS use
WGS-84
What type of signal does a GNSS satellite produce
Broadcast
What frequency signal does GNSS transmit
UHF. 1.2-1.6 GHz
What are the 2 levels of service GPS offers
- Standard
2. Precise positioning
Who uses Precise positioning and is it encrypted
US Military & approved foregin powers
What are the 3 elements/ segments of GPS system
- Space
- Control
- User
How often do space segment satellites orbit the earth?
Approx 12hrs
What are the 2 main components associated with the user segment
Portable, hand held receivers
Recievers permanently installed in aircraft
What is the required accuracy for a particular nav route called and what is the actual GPS accuracy called?
Required Nav Performance
Actual Nav Performance
What are the 7 GPS limitations and errors
- Ephemeris Error
- Ionoshpheric error
- Tropospheric propagation error
- Multipath error
- Clock error
- Receiver noise
- Sattelite availability
An aircraft does not contain an atomic clock, how does it compute position for each sattelite?
Pseudo-range (time measurement from each sattelite)
What does Ground based augmentation system (GBAS) do?
Uses a VHF link to aircraft to transmit:
- locally relevant corrections
- integrity data
- approach data
What does Aircraft based augmentation system (ABAS) do
Uses onboard equipment to overcome the performance limitations of GNSS
What are the 2 ABAS currently in use
- Reciever auto integrity monitoring
2. Aircraft auto integrity monitor
What does RAIM do
Determine if a sattelite is providing corrupt info
What does AAIM do
Uses position from aircrafts INS and other sensors as an integrity check of GNSS, when RAIM is unavailable
What can further GPS accuracy?
By using differential stations
Is UHF virtually unnaffected by weather?
Yes
How mang GLSSU does the pc21 have?
2
Briefly explain the types of GNSS limitations and errors
- Ephemeris: Error inherent to satellite position data
- Ionospheric: apparent change of speed of light in ionosphere
- Tropospheric propagation effect: water vapour in troposphere delays satellite signal
- Multipath: signal bounces off multiple signals before getting to reciever
- Clock: sattelite atomic clock becomes out of alignment with reference clock
- Reciever noise: unwanted disturbances superimposed on signal obscuring signals usefulness or content
