Navigation and Seamanship (1+1)

3.1.6. Basic Principle of echosounder

Sound waves are directed in the same way as light waves in a searchlight, towards the bottom of the sea floor. A pulse of sound sent from the ship is get reflected as echo after hitting the sea bottom. The time interval between transmission of sound wave and the reception of bounced echo is being proportional to the depth of the water. Water depth is determined from the travel time and the speed of sound in water. Water depth can be estimated simply by using an average sound speed and the following relationship:

Distance between vessel and sea bottom = speed of the sound wave in water multiplied by travel time of sound wave send from vessel and reception of echo by vessel divided by two. The value is divided by 2 as the sound wave travels two way from vessel to sea bed and seabed to vessel . In order to understand the acoustic function of an echo sounder one must know the basics of Hydroacoustics that means study about propagation, reflection and refraction of sound waves in water.