### ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

## 2pUW23. The effect of roughness on acoustic penetration of the seafloor as
given by a fluid--fluid perturbation model and comparison with recent sediment
penetration experiments.

**John E. Moe
**
Eric I. Thorsos

Darrell R. Jackson

Kevin L. Williams

**
**
*Appl. Phys. Lab., Univ. of Washington, 1013 NE 40th St., Seattle, WA
98195
*

*
*
Recent experimental results [F. E. Boyle and N. P. Chotiros,
2615--2619 (1992)] reveal acoustic penetration from water into sandy sediments
at grazing angles below the compressional critical angle in relation to the
mean surface. These authors interpret the results to indicate the excitation of
a biot slow wave in the sediment. An additional mechanism for subcritical
penetration will be discussed, based on assuming a small level of roughness at
the water--sediment interface. Computer simulations of these experiments using
theoretical calculations based on Rayleigh--Rice perturbation theory for 2-D
surfaces reproduce experimental results, indicating that the acoustic
penetration of the surface may be due to scattering (diffraction) from low
levels of roughness. The accuracy of perturbation theory for the level of
roughness being considered is verified using comparisons with exact
calculations in the special case of 1-D surfaces. [Work supported by ONR.]