Oceanography (2+1)

Sound transmission in sea water

Sound is a form of mechanical energy which can be described as a periodic variation in pressure, particle velocity or displacement in an elastic medium. In general, sound propagates very well in liquids. Water transmits sound more efficiently than the atmosphere. Sound travels at a faster rate and with less absorption of energy through water than through the air.

Application of sound transmission in sea water

The propagation of sound in the ocean is of special importance since it has many applications. Sound is useful to find depths in the ocean. The echo sounder measures the depth of the water under a ship’s hull by estimating the time required for a sound pulse to travel to the sea floor and back to the ship. Sound can be used to locate objects, sense their shape and determine their distance away from the sound’s source. The properties of the sea floor can be detected by studying the echo charts obtained by means of an echo sounder, since some sea floor materials. Sometimes, a special type of underwater phenomenon is detected on the depth chart of the echo sounder. Several marine organisms including fish move up towards the surface during night time and sink down to deeper waters during day time. These organisms form a layer known as the “deep scattering layer”. A portion of the sound beam is scattered and reflected by the deep scattering layer creating the image of a false bottom on the echo sounder chart. Thus, sound transmission is useful to find the depth of availability of fish in the sea. Underwater sound propagation has important military applications also, particularly in submarine detection and echo ranging. In the sea, sounds are produced very frequently by three groups of animals, namely; fish, crustaceans and mammals including whales. Hydrophones are used to listen to the sounds of these animals. Analysis of these sounds will help in identifying their sources.