Doppler Log

Question 1

What does the Doppler log do?

Answer 1

• Measures the speed with respect to the surface
• reflecting the transmitting wave.

Question 2

What’s a good depth for the wave to be reflected?

Answer 2

200m

Question 3

What does the difference between the 2 frequencies calculate?

Answer 3

Speed

Question 4

What’s the beam width and frequency?

Answer 4

3 degree wide
100-600 KHz

Question 5

Why is it the most common on all craft?

Answer 5

Easily fitted

Good accuracy especially at low speed.

Question 6

What’s the optimum angle for transducer function?

Answer 6

• 60 degrees ahead of the vessel.
• if more than 60 it won’t be able to obtain reliable speed readings.

Question 7

How is the actual speed computed?

Answer 7

• From the Doppler shift of signal frequency
• from transmission to reception.

Question 8

The transducer reflects pulses off what?

Answer 8

Reflects pulses of energy to the seabed or partials 10-30m off the keel.

Question 9

What’s bottom tracking mode?

Answer 9

• Provides SOG
• Energy reflected off seabed.

Question 10

What’s water tracking mode?

Answer 10

• Used in deep water.
• Sound energy is reflected off layers. = STW

Question 11

Janus configuration effect?

Answer 11

Effect is to cancel out errors caused by pitching and trim of vessel.

Question 12

Why do we have the janus configuration effect?

Answer 12

• Due to pitching

This motion can interfere with certain operations, such as-
* acoustic navigation
* sonar detection
* other precision instruments.

Question 13

What’s aeration?

Answer 13

• Tempreature and salinity causes changes to speed of sound in water.

Question 14

Advantages of Doppler log?

Answer 14

• Accurate
• STW and SOG
• Better at birthing, reversing, low speed.
• Resistant to fouling.
• Independent of weather conditions

Question 15

Name some causes of errors

Answer 15

• Aeration
• Heaving pitching and rolling
• Damaged transmitter or receiver
• Water moving at different velocity to surface layer