Analysis of laboratory measurements of sound propagating into an unconsolidated water-saturated porous media

Abstract

A series of measurements in the NRL shallow-water laboratory have been conducted to understand the propagation of sound into and within an unconsolidated water-saturated porous medium. The initial set of measurements was taken to quantify sound penetration as a function of incident angle and interface roughness and to identify the types of waves generated within the water-saturated sandy bottom. These investigations included two-dimensional synthetic array measurements for both a smoothed and a roughened interface. Additionally, above interface and buried source, one-dimensional synthetic array measurements were taken to investigate specifically the types of compressional waves generated within the sandy bottom. To complete the physical characterization of the wave speeds propagating in the bottom, measurements of the shear wave speeds have been made. These measurements provide a large data base for analysis to understand the physics of this sandy bottom, which consists of a 3.0-m-deep bed of a manufactured 212-μm mean diameter sand. Analysis of these measurements using Biot models and other fluid models is presented. In addition, analysis of enhanced sound penetration at shallow grazing angles due to a roughened interface is discussed. [Work supported by ONR.]