Time‐frequency analysis of mode coupling in shallow‐water sound propagation

Abstract

Time‐frequency (TF) analysis for propagation of broadband sound pulses in shallow water in presence of perturbations of waveguides parameters, such as internal waves, temperature fronts, or bottom variability is considered. Due to waveguide dispersion one can construct a TF diagram for individual normal modes using Gabor transform for each received pulse. If we have a temporal sequence of propagating pulses then we can find a temporal sequence of TF diagrams. It is shown that in the presence of spatial and temporal waveguide perturbations (such as the sound‐speed profile in the water column or the sea bottom) structure of a TF diagram and its temporal behavior depends on waveguide parameters, on the source‐receiver positions, and on the character of mechanisms influencing the sound propagation, such as mode coupling, horizontal refraction, or adiabatic regime. Dependence of the TF diagram on waveguide variability in geotime provides information about temporal behavior of the perturbations. Structure of TF diagram is analyzed for a shallow‐water waveguide model as well as for the SWARM95 experimental data. [Work supported by ONR and RFBR.]