Page 43 - Electronic Navigation Cyber Book

If the source and listener are moving closer to each other, the listener will
perceive a higher frequency - the faster the source or receiver is
approaching the higher the Doppler shift.
If the source and listener are getting farther apart, the listener will
perceive a lower frequency - the faster the source or receiver is moving
away the lower the frequency.

The Doppler shift is directly proportional to speed between source and
listener, frequency of the source, and the speed the wave travels.
In above figure ‘v’ is the velocity of sound, and the propagation speed is ‘
c’, every wave is shortened due to the movement of the source by ‘d’

The Doppler log is based on measurement of the Doppler effect.

It is seen that an observer, moving with a source of sound towards a
reflecting plane, receives a frequency:

Where fv is the received frequency, f the transmitted frequency, c the
speed of sound and v the speed of the source of sound.

Principle

A transmitting transducer below the ship continuously emits a beam of
sound vibrations in the water at an angle (usually 60˚ to the keel) in the
forward direction.

A second transducer aboard receives the echo caused by diffuse
reflection from the seabed.

A Doppler log uses a higher frequency than an echo sounder.

© 2018 Digital Galaxy Index 43