Measurements of acoustic wave speeds in a fluid-saturated sandy bottom

Abstract

A new laboratory has been created at NRL to study the physics associated with the scattering from buried and partially buried objects in a saturated porous media environment. The laboratory consists of a 600 000-liter deionized water tank that is instrumented with precision robotic scanners and sources and receivers for broadband (0.5 kHz–5 MHz) acoustics research. Presently, the tank is filled with a 3.0-m-deep bottom of 212-mm-mean-diam sand that has been filtered and cleaned. Preliminary measurements of the acoustical wave sound speeds propagating in this saturated porous media are presented. In addition to time-delay measurements, similar to those done by Chotiros [J. Acoust. Soc. Am. 97 (1995)], a novel synthetic array was used to map the wavefronts propagating through the bottom. From these two-dimensional synthetic array measurements, wave speeds are evaluated using analytical techniques that include wave-number frequency and ray path analysis. Attenuation in the porous media and reflection and transmission from the interface are also studied. [Work supported by NRL.]