Sound speed meter


A speedometer measures the speed of sound in the water. It's a device that lets the water in a cable. The measured values ​​are digital and are passed on to a computer.

To determine a correct sound velocity profile c (m / s), a number of data are needed, including the salt content S (in ‰), the depth D (in m) and the seawater temperature t (in ° C) . There are several empirical formulas, such as those of Medwin, Wilson and Horton, to calculate the sound speed.

For direct measurement of the sound velocity, use the so-called 'sing around velocity' meter. A high-frequency pulse is transmitted by a transducer, about ten times the speed of sound in meters per second. The pulse is then reflected after retrieval of a known distance (d) and then retrieved by the transducer.

This shows that the pulse duration corresponds to the period of transmitted pulses, so that the pulse frequency can be measured very accurately. By measuring them now, from the known distance and the measured frequency (f), the sound velocity (c) can be calculated by c = 2 * d * f.

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