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# Doppler Log Principle

## PRINCIPLE

Doppler log is based on the principle of “Doppler Shift Effect”, i.e., apparent change in frequency received (from what was transmitted) when the distance between source and observer is changing due to the motion of either source or observer or both. In Doppler log an observer is moving with a source of sound towards a reflecting plane, then the received frequency:

fr = ft (c+v) / (c - v)

where,

ft = transmitted frequency

c= velocity of sound in seawater and

v = velocity of the vessel

By measuring the received frequency (fr) & knowing the value of transmitted frequency

(ft) and velocity of sound in seawater (C), the speed of the vessel y can be determined.

## GENERAL DESCRIPTION

A transducer is fitted on the ship’s keel which transmits a beam of acoustic wave at an

angle c usually 60° to the keel in the forward direction, this gives the component “ v cos

𝜶” of the ship’s velocity towards the sea bed thus causing the Doppler shift and the

Inserting value of velocity vcos

fr = ft ( c + v Cos 𝜶)/(c - v Cos 𝜶.)