Long‐range continuous‐wave and time‐domain simulations of ocean acoustic scatter from a subbottom anelastic corner

Abstract

Recent long‐range acoustic reconnaissance experiments done in the mid‐Atlantic ridge region show strong reverberation from many ocean bottom features. Two types of features characteristic of this region, and possible contributors to this reverberation, are seafloor ridge corners—‘‘inner’’ corners and ‘‘outer’’ corners—formed by two ridge faces intersecting at near‐right angles. Corners formed by faces intersecting at near 90° are termed ‘‘inner’’ corners and those formed by faces intersecting at near 270° are termed ‘‘outer’’ corners. Via computer simulations, the effects of an anelastic seafloor corner on the acoustic field originating from a distant source have been investigated. Both an ‘‘inner’’ corner and an ‘‘outer’’ corner were used in the study. The effects of thin sediment layers covering the corners were also investigated. Simulations were made using continuous‐wave (cw) computer models: the parabolic equation model, fepe, for long‐range propagation of the acoustic fields to and from the vicinity of the corners, and the seismoacoustic finite‐element model, safe, to determine the scattered fields from the anelastic corners. Time‐domain calculations were obtained from FFTs of the cw fields. Examples will be presented that show the effects from these two corner types. [Work supported by NRL, ONR, and the ONR Acoustic Reverberation SRP.]