How does an echo sounder determines the depth below the ships?

How does an echo sounder determines the depth below the ships?

What is an echo sounder?

An echo sounder is also known as Echo sounding equipment makes use of sound propagation technique to provide reliable information on depth of water. In order to navigate safely, it is important to know the depth below the ship.


The echo sounder is thus designed to provide reliable information on depth below the ship basically to aid navigation. A transducer is placed under the ship.


What is principle of working?

Echo sounder works by transmitting sound waves into the water. The time interval between the emission and return of a pulse is recorded

Let’s see how to determine the depth below the ship by echo sounding

The short pulse of the sound energy (acoustic pulses) are transmitted vertically down from the ship and is reflected back as echo after striking the sea bed. The time taken for the return of the echo depends upon the depth of water and speed of sound through water.

The speed pf sound through water=1500m/s

Velocity of sound in water can vary upon temperature and salinity

Distance =speed * time

Depth= distance/2 because the sound waves travels twice the distance of depth

Therefore, Depth =(speed *time)/2

Parts of echo sounder

1. Display unit


This is located on the navigational bridge. The display unit can be paper recording type or digital display type. The main function of this unit is to record and display the depth after measuring.

2. Pulse generator

This produces electrical pulses which are sent to a transducer. The pulse generator can be generated in into display unit or completely separated depending upon the manufacturer.

3. Transducer

This is located at the bottom of the ship in a tank called transducer compartment. the transducer converts electrical pulses into sound waves (acoustic energy). at a frequency of 12khz to 200khz. An internal clock starts this time. these pulses are directed towards the sea bed with the help of transducers and when the pulse are reflected back from the seabed , the transducer converts the reflected sound waves into electrical pulses.



the electrical signals received from the transducer are passed through an amplifier to increase the strength of the received signal. The internal clock notes the time when the pulse is returned and so the time taken is measured.

Block diagram


As illustrated in the above block diagram, the pulse generator generates the pulse. This pulse passes through the transducer. The transducer converts the electrical energy into acoustic energy. this goes down to strike the seabed, then the internal clock starts.

After striking it come back. then this acoustic energy is converted back into electrical energy. And it passes through the amplifier to increase the strenght and it is then recorded on the recorder display unit.