Depth of the sea is measured by two basic methods: by using the acoustic echo sounders on the ships and by using data from the satellite altimeters. As the name suggests, the echo sounders measures the depth of the sea by using echo of sound as measure. The instrument transmits a 10-30 kHz sound and records the echo of that sound that gets reflected from the sea floor. The echo from the floor determines the depth of the sea. Gravity is a factor that influences the sea level. The altimeters use the shape of the sea surface to determine the depth of the sea based on gravity.
Echo sound measurement
Most of the maps of the seas are based on the echo sounder measurement. The areas which could not be measured earlier have now been done so with the help of the altimeters. The echo sounders use SONAR (the sound navigation and ranging) technology to measure the depth of the sea. There are two different types of technology that use the name (SONAR): the passive sonar and the active sonar. The passive SONAR is used to listen to the sounds made by the vessels in the sea. The active SONAR is for listening of echoes and pulses of sounds. The active SONAR assists in measuring the depth of the sea.
The echo sounder works on the principle of reflection of an echo. The echo of waves is transmitted by a wave generator and the time of the return of the wave is noted. This is how the depth of the sea is commonly determined. It is used by ships on cruise to avoid shallow waters.
Fathom is the unit which is used to measure the depth of the sea. Fathom is a unit of length in the imperial system and is symbolized by “ftm”. There are two yards or 6feet in a fathom. All sea maps and measures are expressed in fathom. However the modern nautical charts use meters to express the depth of water or sea.
