A method of calculating propagation loss of sound wave in air from an underwater sound source

Abstract

In order accurately to calculate the transmission loss of sound waves in air from an underwater sound source, a sound propagation loss calculation model was established based on an underwater virtual sound source and geometrical acoustics. Viewed in the air, sound waves seem to spread from a virtual source located at a point underwater in the reverse extension line of the refracted sound rays. Thus the spreading loss of wave surface in the air should be calculated in accordance with the centre of the sphere at the place of virtual source. In the case of two very near sound rays emitted by the sound source, the reverse extension lines of their refracted sound rays necessarily intersect at the underwater virtual source. By finding the derivative of both sides of the Snell's law equation expressed by the product form, the derivatives of the incidence angle and the reflection angle in the relationship would be eliminated. It would then be able to determine the distance from the virtual source to the incident point and also the depth of the virtual source, which in turn would make it possible to calculate the sound transmission loss accurately in air. The measured and calculated values conform quite well, which indicates that the method is correct.