Lateral waves at the ocean-bottom interface: A feasibility study for geoacoustic inversion using horizontal arrays

Abstract

Lateral waves are the cw counterpart of head waves, the latter being sometimes used for geoacoustic inversion [Godin et al., 1999; Berger and Buckingham, 2000; Choi and Dahl, 2004]. They should be detectable at horizontal ranges r that satisfy the criterion H2/(5λ)>r>4h1h2/λ, where the various symbols refer to the water depth, height above bottom of source and receiver, and wavelength in water column. The exent of the usable ranges can be increased appreciably if an end fire (parametic) array is used to direct sound so that the beam hits the bottom interface at the critical angle. Because lateral waves are the diffraction spill-off of energy carried primarily in the bottom, they have the potential for yielding geoacoustic parameters such as bottom attenuation and sound-speed profiles. Textbook models predict waves that radiate up from the bottom at the critical angle; more realistic models suggest a distribution in angles, with the distribution varying with range and depending on the bottom sound-speed profile. Horizontal arrays yield information on this angle distribution. Developed theory uses Biot low-frequency model for the bottom and matched asymptotic expansions.