gnss Flashcards
what does gnss stand for and who has it?
global navigation satellite system.
america - gps
russia - glonass
japan - qzss
eu - galileo
what are the segments of a gnss
space - satellites
control - ground-based stations
user - receivers
how does gnss work?
using trilateration, finding distance with spheres, where satellite broadcasts a signal which travels 360 degrees in every direction.
what does gnss transmit?
a pseudo-random code that identifies the satellite, the time of transmission of the code and the satellite position at that time.
what is multi-path error?
when gnss signals bounce off terrain.
this may cause a receiver to receive a signal from the same satellite twice, but at different times.
what is the tropospheric effect?
as the system uses the time a signal takes to each receiver to calculate range and power,
the troposphere which contains water vapour slows the satellite signals down.
what is the ionosphere?
a layer of charged particles (ions) stretching 80 - 640km above the earths surface.
it overlaps the beginning of space and changes in depth based on the time of day, season and solar activity.
what does ionospheric delay do?
as radio signals are electromagnetic.
ionosphere interferes with the speed that satellite signals pass through it, thus producing an error in the range of the receiver.
are gnss signals strong from satellites? which means what?
no
meaning they can be swamped by other transmissions including radio and tv stations, radar and VHF radio signals.
what can satellite interference do to gnss?
cause the gnss receiver to have no satellite signal, in which case no position can be obtained.
or it can degrade the signal to an extent where an accusation position is not obtainable.
what is Geometric dilution of position (GDOP)?
relates to the error cause when satellites are closer together, meaning GDOP is increased and position accuracy is reduced.
what causes receiver error?
- receiver rounding off calculations that it performs in order to calculate position
- receiver not being able to receive a strong enough signal from satellites.
- clock error. gnss receivers use a quartz clock which is less accurate tan the atomic clocks satellites use.
what is fiddle factor?
pilot being tempted to try out all the buttons and modes of a gnss receiver.
what is the precaution with entering data into the keypad?
how is this amplified?
if an incorrect destination is entered, the receiver has no means of knowing this and will lead to the location entered.
amplified if an autopilot is coupled to the gnss, where it’ll fly you the wrong way
what is mode error?
having gnss in the wrong mode (since they can have multiple) can mean that the information it provides or sends to the autopilot is incorrect for that stage of flight.
