Future shallow water low frequency (100–1000 Hz) acoustic signal propagation physics studies

Abstract

The measurement and prediction of the phase and amplitude properties of acoustic signals (1 to 1000 Hz) propagating in the dynamic shallow water (30 to 500 m water depths) environment has been a focus of the underwater acoustic research community for nearly 20 years. The majority of the ocean studies have occurred during late spring to summertime oceanic conditions when the sound speed variability was influenced by nonlinear mode 1 internal wavefields. Sound speed variability during the summer-to-winter and winter-to-summer water column transition periods will cause variability in the phase coherent properties of acoustic signals. Few experimental studies explicitly focused on quantifying the variability of phase coherent properties of acoustic signals during these periods have been performed. Illustration of the types of fluid processes that will perturb the sound speed structure during the fall-to-winter transition periods will be presented. Included will be mode 1 and mode 2 internal wave perturbation of the sound speed field as well as the locations and spatial scales of sound speed variability caused by interleaving water masses of varying temperature and salinity (Spice). Fall-to-winter transition sound speed fields will be contrasted with summer time sound speed conditions. [Work supported by the Office of Naval Research.]