APPENDIX VI: Basic Acoustic Theory
Figure 136: In 1822 Daniel Colloden used an underwater bell to calculate the speed of sound under water in Lake
Geneva, Switzerland at 1435 m/Sec, which is very close to recent measurements.
12 APPENDIX VI: Basic Acoustic Theory
12.1 Introduction
With multibeam, as with any echosounder, a main concern is: sound in water. Once the projector
transmits the acoustic energy into the water, many factors influence that energy’s velocity and
coherence. The major influence is the velocity of sound in water.
12.2 Sound Velocity
The major influence on the propagation of acoustic energy is the sound velocity of the water
column. As the acoustic pulse passes through the water column, the velocity and direction
(refraction) of the wave front will vary based on the water column sound velocity. If the sound
velocity, through the water column, is not accounted for in the data collection software the depths
and the depth location will be in error. For this reason, sound velocity casts are an oft repeated
routine during multibeam survey.
Page 141 of 210
Version 5.0 Rev r002
Date 05-08-2014
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