Doppler Log Flashcards
What does the Doppler log do?
- Transmits an acoustic pulse at a known frequency
- and monitors change in frequeny of the returning pulse
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.
- 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 -
This motion can interfere with certain operations, such as -
- acoustic navigation
- sonar detection
- other precision instruments.
What’s aeration?
- When the vessel moves through water, especially in rough seas
- air bubbles can form near the hull and interfere with the acoustic signals that the Doppler log relies on.
Advantages of Doppler log?
- Accurate
- STW and SOG
- Better at birthing, reversing, low speed.
- Resistant to fouling.
Name some causes of errors
doppler log
- Aeration
- Heaving pitching and rolling
- Damaged transmitter or receiver
- Water moving at different velocity to surface layer
