Passive acoustic monitoring of coastal dynamical oceanographic phenomena using single hydrophone

During long term passive acoustic monitoring in shallow water in Iroise Sea, the time series of the ambient noise recorded with a single hydrophone showed some unusual striations in the time-frequency domain. The changes in the striation slopes are related to the tidal oscillations, which induce a change in the water depth of the waveguide. The observed striations are highly correlated with the tides, and this phenomenon is classically described by a simple scalar γ called the depth-frequency waveguide invariant. However, the observed invariant γ_obs ≃ -1 differs from the canonical γ = -2 value. A theoretical approach is developed to explain the observed γ_obs, and particularly its dependence on the bathymetry in a range-dependent environment.