Acoustic pressure reflection coefficients of a subsurface bubble layer in water

Abstract

Acoustic scattering and absorption of a bubble layer near the ocean surface are very important information to understand sound propagation in the ocean. Such a subsurface bubble layer plays significant roles as a source and a scatterer of underwater sound. The acoustic pressure reflection coefficient from bubbly liquids is theoretically derived from a three-medium analysis for the subsurface bubble layer. The reflection coefficient from the subsurface bubble layer is also experimentally measured at normal incidence in water and compared with the prediction obtained from the three-medium analysis. It is found that most of the sound waves are reflected near the resonance frequencies of individual bubbles in the subsurface bubble layer. The reflection coefficients at the resonance frequencies are strongly affected by the bubble size distribution of the bubble layer, and the amplitudes of reflected waves are affected by the void fraction. The theoretical predictions of the reflection coefficient are in good agreement with the experimental measurements. The small discrepancies between predictions and measurements may be due to the uncertainty in the measurement of the bubble size distribution of the bubble layer.