Simulation of an underwater acoustic communication channel characterized by wind-generated surface waves and bubbles

Abstract

Sea surface scattering by wind-generated waves and bubbles is regarded to be the main non-platform-related cause of the time variability of shallow acoustic communication channels. Simulations for predicting the quality of acoustic communication links in such channels thus require adequate modelling of these dynamic sea-surface effects. It is known that, for frequencies in the range 1-4 kHz, the main effect of bubbles on sea surface reflection loss is due to refraction, which can be modelled with a modified sound-speed profile accounting for the bubble void fraction in the surface layer. The upward refraction induced by the bubble cloud then effectively acts as a catalyst for increasing the rough-surface scattering. In the present work, it is shown that, for frequencies in the range 4-8 kHz, bubble extinction also provides a significant contribution to the surface loss, including both the effects of bubble scattering and absorption. As this is the frequency band adopted in the EDA-RACUN project, in which the reported research has been conducted, both bubble refraction and extinction effects should be modelled for acoustic channel simulations in RACUN. These model-based channel simulations will be performed by applying a ray-tracer, together with a toolbox for generation of rough sea-surface evolutions.