Acoustic scattering by internal solitary waves in the Strait of Gibraltar

Abstract

High-frequency underwater acoustic transmissions across the Strait of Gibraltar were used to examine acoustic scattering caused by the unique internal wave field in the Strait. Internal solitary waves of 100 m in amplitude propagate along the interface between an upper layer of Atlantic water and a lower layer of Mediterranean water. The interface is also strongly modulated by internal tides of comparable amplitude. As internal solitary waves cross the acoustic path, they cause sharp soundspeed gradients which intermittently refract acoustic rays away from normal sound channels. Internal tides vertically shift soundspeed profiles for additional travel time variability. Although the acoustic scattering is quite complicated, it is also surprisingly robust, making it a good candidate for modeling. Key features of the acoustic arrival pattern can be accounted for in some detail by a model description of the complex hydraulics in the Strait.