Effect of the wind-generated bubble layer on forward scattering from the ocean surface

Wave scattering from pressure release surfaces is a classical subject with a long history. The standard approach which treat the surface probabilistically has been well developed. Over the last decade, some problems are more effectively solved with the deterministic approach. However, the complexities of upper ocean affect acoustic scattering from the ocean surface, and wind-generated bubbles are one of the most important complexities. In this paper, the effect of wind-generated bubble layers on forward scattering from the ocean surface is studied. The extended Hall-Novarini model is used to describe the population spectral density of the bubble layer. The time-domain Helmholtz-Kirchhoff integral is used to describe the acoustic scattering from pressure release surfaces. The free-field Green’s function for an inhomogeneous medium is formulated using ray method. The advantages of such conjunction are as follows: (1) the geometric shadowing effects generally neglected in the H-K integral can be handled by ray method; (2) the Helmholtz-Kirchhoff integral can provide a correct solution even in caustics zones. The numerical simulation reveals that, for large wind speeds, the amplitude of scattering signal is negligible in contrast to the amplitude of direct path signal. In such situation, the reverberation will be dominated by volume scattering of wind-generated bubbles.