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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 ...
This keeps the returning echo in the same frequency range as the normal echolocation call. This dynamic frequency modulation is called the Doppler shift compensation (DSC), and was discovered by Hans Schnitzler in 1968. [1] CF bats employ the DSC mechanism to maintain the echo frequency within a narrow frequency range. [2]
For a linear time-invariant system, the relationship between the acoustic pressure applied to the system and the resulting acoustic volume flow rate through a surface perpendicular to the direction of that pressure at its point of application is given by: [citation needed]
Pulse compression is a signal processing technique commonly used by radar, sonar and echography to either increase the range resolution when pulse length is constrained or increase the signal to noise ratio when the peak power and the bandwidth (or equivalently range resolution) of the transmitted signal are constrained.
Three common methods are used to calculate the Doppler shift and thus the water velocity along the acoustic beams. The first method uses a monochromatic transmit pulse and is referred to as "incoherent" or "narrowband". The method is robust and provides good quality mean current profiles but has limited space-time resolution.
One area of research in which attenuation plays a prominent role, is in ultrasound physics. Attenuation in ultrasound is the reduction in amplitude of the ultrasound beam as a function of distance through the imaging medium. Accounting for attenuation effects in ultrasound is important because a reduced signal amplitude can affect the quality ...
The transceiver head normally contains three or more transducers separated by a baseline of 10 cm or less, hence the "short baseline" name. A method called “phase-differencing” within this transducer array is used to calculate the direction to the subsea transponder. The presence of environmental noise reduces USBL positioning accuracy.
Range ambiguity resolution is a technique used with medium pulse-repetition frequency (PRF) radar to obtain range information for distances that exceed the distance between transmit pulses. This signal processing technique is required with pulse-Doppler radar .