Application of Warping Transform for the Analysis of the Acoustic Mode Coupling due to a Local Inhomogeneity in Shallow Water

The possibility of observing the mode coupling effect, caused by a local inhomogeneity, is studied for a long-range stationary acoustic track between a single sound source and a single receiver in a shallow-water waveguide. This effect manifests itself in the form of oscillations of normal mode amplitudes in the frequency domain and can be used to localize inhomogeneities. An analytical formula linking the oscillation period of the first-mode amplitude with the distance to the inhomogeneity is proposed. Numerical experiments with a model inhomogeneity in the form of a local bottom rise show that the frequency dependence of the mode amplitude can be selected not only at a vertical line array but also at a single receiver, with the use of warping transform. In this case, the receiver depth should correspond to zero of the second-mode vertical profile. The dependence of the mode amplitude oscillations on the local inhomogeneity size is discussed.