Acoustic head waves in oceanic waveguides

Abstract

Wave and ray theories of head (lateral) waves are reviewed, including effects due to absorption, stratification, source directivity, and roughness of interfaces. While the wave theory is instrumental in determining head-wave amplitude and region of existence, the ray theory of head waves is particularly helpful in extending results to multilayered structures and horizontally inhomogeneous environments. Physical significance of the head wave is discussed. As far as inverse problems are concerned, head waves offer a rather direct way of measuring certain physical and geometrical characteristics of the ocean bottom. Head waves typically have smaller amplitudes than other components of the acoustic field in a waveguide, but still can be reliably identified and measured, especially where they are spatially or temporally separated from the more energetic field components. Shallow-water environments are shown to complicate the arrival structure of head waves and their modeling, while providing additional opportunities for retrieving useful geoacoustic information from head-wave data. Application of the head-wave theory to determination of geoacoustic parameters of a stratified ocean bottom, including compressional wave attenuation, is illustrated using data obtained during the Pacific Shelf-93 experiment. [Work supported in part by ONR.]