Scattering from an object in a stratified medium. I. Frequency dispersion and active localization

A signal scattered from an extended object is often very different from a point source signal emitted from the object. Hence active localization based on matched‐field/mode processing may not be feasible, depending on how the signal is modified by scattering. In a stratified medium in which propagation of a signal can be expressed in terms of normal modes, the effect of scattering is to induce mode coupling—an incident normal mode is converted to a series of outgoing normal modes by the scatterer. This mode coupling is examined by ensonifying the object with a broadband pulse at some distance from the object. The time‐frequency dispersion of a scattered signal is compared with the dispersion of a passive signal traveling the same path (with the scatterer absent). One finds that the coupled normal modes (created by scattering) arrive at a different time than the uncoupled (original) normal modes and can be identified using time‐frequency analysis. For active source localization broadband matched‐mode proce...