Doppler Log Flashcards
What does the Doppler log do?
Measures the speed with respect to the surface reflecting the transmitting wave.
What’s a good depth for the wave to be reflected?
200m
What does the difference between the 2 frequencies calculate?
Speed
What’s the beam width and frequency?
3 degree wide
100-600 KHz
Why is it the most common on all craft?
Easily fitted
Good accuracy especially at low speed.
What’s the optimum angle for transducer function?
60 degrees ahead of the vessel.
Otherwise if more than 60, it won’t be able to obtain reliable speed readings.
How is the actual speed computed?
From the Doppler shift of signal frequency from transmission to reception.
The transducer reflects pulses off what?
Reflects pulses of energy to the seabed or partials 10-30m off the keel.
What’s bottom tracking mode?
Provides SOG
Energy reflected off seabed.
What’s water tracking mode?
Used in deep water.
Sound energy is reflected off layers. = STW
Janus configuration effect?
Effect is to cancel out errors caused by pitching and trim of vessel.
Why do we have the janus configuration effect?
Due to pitching, an error is introduced therefore is overcome by having 2 acoustic beams. One directed ahead. And one astern.
What’s aeration?
Temp and salinity causes changes to speed of sound in water.
Advantages of Doppler log?
Accurate
STW and SOG
Better at birthing, reversing, low speed.
Resistant to fouling.
Independent of weather conditions
Name some causes of errors
Aeration
Heaving pitching and rolling
Damaged transmitter or receiver
Water moving at different velocity to surface layer
