Resonances in acoustic bottom reflection and their relation to the ocean bottom properties

Abstract

The acoustic reflection coefficient of the ocean bottom plotted versus frequency or angle often exhibits a complicated structure of peaks and dips. Features as these may be attributed to resonance phenomena, and the resonance structure, i.e., the distribution and the widths of the resonances, is found to contain essentially all relevant information about the interacting medium. Interpreting the reflection coefficient as a series of antiresonances and applying our previous resonance formalism (i.e., approximating the exact form of the resonant amplitude by Breit‐Wigner resonance shapes), one finds a direct link between measurable quantities (locations and widths of resonances) and medium properties, thus enabling us to solve the inverse scattering problem. We demonstrate this approach by the example of a liquid layer imbedded between two different liquid, semi‐infinite media. We then show explicitly the connection between the resonance data and the medium properties (densities, sound speeds, and layer thickness). For realistic models of the ocean floor, additional features (shear wave propagation, attenuation, density, and velocity gradients) must be included. The implication of this on the formalism will be discussed.