This paper presents a numerical analysis method for estimating reflected transient waves from an object in the water by using transfer functions which can be calculated by the boundary element integration method (BEM). By this method, reflected waves for four types of incident transient signals from the submerged rigid sphere which is coated with a thin rubber layer are estimated.

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As a part of the study of “underwater transmission system” for divers, we investigated an ability of underwater sound localization in man by means of the hearing tests in the pool. As a result, it was found that the man is able to discriminate the direction of underwater sound. Although the values of minimum audible angle in water increased by about one digit compared with that in air, the tendency of MAA to the azimuth was similar to the case in air. We assumed a simple sound propagation model due to the fact that the hearing in water mainly depends on the transmission of bones such as a cranium and considered the mechanism of underwater sound localization in man. As a result, it was found that the threshold for a change in time difference Δt_th shows the constant value in the audible frequency range and its value is almost equal to the case in air below 1300 Hz. Therefore, it is considered that the underwater sound localization in the audible frequency range is carried out by a time difference or a phase difference of sounds between the ears.

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