sonar

It is a finding that Popper says “should not be extrapolated to other fish species or the effects of other sound sources.” There is considerable concern that human-produced (anthropogenic) sounds added to the environment could have damaging effects on marine life.

Sonar are electronic devices that use the principle of an echo to detect and locate object. Sonar uses the echo principle by sending out sound wave under water or through human body to locate objects. Sound Waves are a type of acoustic energy.

Depth finder, also called echo sounder, device used on ships to determine the depth of water by measuring the time it takes a sound (sonic pulse) produced just below the water surface to return, or echo, from the bottom of the body of water.

echo sounder, an older instrumentation system for indirectly determining ocean floor depth. Echo sounding is based on the principle that water is an excellent medium for the transmission of sound waves and that a sound pulse will bounce off a reflecting layer, returning to its source as an echo.

Echo sounder measures the depth of water by measuring the time for a pulse of energy to travel to the sea bed and back and work on the principle of reflection of acoustic energy. Short pulse of sound energy is transmitted vertically down from the ship.

Applications of echoes – example Echoes are used by bats, dolphins and fisherman to detect an object / obstruction. They are also used in SONAR (Sound navigation and ranging) and RADAR(Radio detection and ranging) to detect an obstacle.

To ensure the correct sound velocity (SV) is used, a bar check should be conducted before the survey commences. The bar check involves lowering a flat plate below the echo sounder transducer to several known depths below the surface and comparing the actual versus measured depth.

Echo sounding is a type of sonar used to determine the depth of water by transmitting acoustic waves into water. The time interval between emission and return of a pulse is recorded, which is used to determine the depth of water along with the speed of sound in water at the time.

It works on the principle of transmitting sound waves from ship’s bottom and then measuring the time taken for the echo to be returned from sea. If the velocity of sound in water is known the time will be proportional to the distance travelled.

Echo-sounders are classified into two types; Single-Beam Echo Sounder (SBES) and Multi-Beam Echo Sounder (MBES). The names of ‘single’ and ‘multi’ stem from the number of depth points measurements collected at the same time.

Single beam echo sounders (SBES), also known as depth sounders or fathometers determine water depth by measuring the travel time of a short sonar pulse, or “ping”. The sonar ping is emitted from a transducer positioned just below the water surface, and the SBES listens for the return echo from the bottom.

The echo-sounder comprises a transmitter, transducer, receiver amplifier and timebase/display.

Unit selector switch

Phasing is a method used in echo sounder to determine depth of the sea bottom. In this method the speed of the stylus is kept constant and the range scale is changed from 0-100 mtrs , 100-200 mtrs , 200-300 mtrs and so on.

The echo-sounder comprises a transmitter, transducer, receiver amplifier and timebase/display. Figure 17 is a block diagram showing the interconnection of these units.

Acoustic depth measurement systems measure the elapsed time that an. acoustic pulse takes to travel from a generating transducer to the waterway bottom and back.

Acoustic methods (also known as sonic testing, vibration testing, mechanical impedance testing) depend on exciting vibrations in a specimen by a local impact and then measuring some properties of the vibrations, eg resonant frequency, decay time, etc.

The depth of the ocean can be measured using a device called SONAR (Sound Navigation And Ranging). Sonar works by sending out sound waves and measuring how long it takes for the echo to return. If the water is shallow, sound waves that reflect off the bottom of the ocean will return faster than in deep sea.

These sound waves can travel for hundreds of miles under water, and can retain an intensity of 140 decibels as far as 300 miles from their source.

Reginald Fessenden