Effects of the sub-surface bubble layer on sound propagation

Abstract

Based on photographic data of bubble populations and theoretical considerations, a formula for the spectrum of wind-generated bubbles in the open sea is derived. This formula is used in a computer study to calculate the full effect of bubbles on refraction and attenuation in sound propagation both in the surface duct and in vertical paths. The study is carried out for frequencies in the range 8–60 kHz, and wind speeds to 30 kn. Attenuation is found to be very significant in this range. For practical purposes formulae for the loss per limiting ray cycle and for the two-way attenuation in a vertical path are obtained by fitting the numerical results. These formulae can be easily implemented on hand-held calculators.