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Echo sounding or depth sounding is the use of sonar for ranging, normally to determine the depth of water . It involves transmitting acoustic waves into water and recording the time interval between emission and return of a pulse; the resulting time of flight , along with knowledge of the speed of sound in water, allows determining the distance ...
"Sonar" can refer to one of two types of technology: passive sonar means listening for the sound made by vessels; active sonar means emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. [ 4 ]
Multibeam sonar is used to map the ocean floor. A multibeam echosounder (MBES) is a type of sonar that is used to map the seabed. It emits acoustic waves in a fan shape beneath its transceiver. The time it takes for the sound waves to reflect off the seabed and return to the receiver is used to calculate the water depth.
Synthetic-aperture sonar (SAS) is a form of sonar in which sophisticated post-processing of sonar data is used in ways closely analogous to synthetic-aperture radar. Synthetic-aperture sonars combine a number of acoustic pings to form an image with much higher along-track resolution than conventional sonars.
Output of a computer model of underwater acoustic propagation in a simplified ocean environment. A seafloor map produced by multibeam sonar. Underwater acoustics (also known as hydroacoustics) is the study of the propagation of sound in water and the interaction of the mechanical waves that constitute sound with the water, its contents and its boundaries.
An acoustic doppler current profiler (ADCP) is a hydroacoustic current meter similar to a sonar, used to measure water current velocities over a depth range using the Doppler effect of sound waves scattered back from particles within the water column.
At high frequency settings, high chart speeds, such fathometers give a picture of the bottom and any intervening large or schooling fish that can be related to position. Fathometers of the constant recording type are still mandated for all large vessels (100+ tons displacement) in restricted waters (i.e. generally, within 15 miles (24 km) of land).
They break down into two broad categories; acoustic and non-acoustic. Acoustic systems in turn break down into active sonar systems and passive sonar systems designed to detect the acoustic signature of submarines such as SOSUS.