Acoustic Properties of Sediments

Abstract

This is a summary of work done at DRL on measurement of acoustic properties of water-saturated sediments. The sediments used were laboratory-prepared to allow control of physical parameters (such as grain size, volume concentration, compressibility, etc.) and to approximate natural sediments. Acoustic velocity and attenuation in the sediments were measured over the frequency range 4–600 kc/sec. Acoustic measurements were made at high frequencies by means of two probes inserted in the sediments and at low frequencies by means of a specially constructed rigid-wall standing-wave tube. The data presented show the frequency dependence of attenuation and velocity in the laboratory-prepared sediments and the change in this frequency dependence with changes in physical parameters of the sediments. Sediments composed of pure clay or clay and sand up to 15% (by weight) show a f1.37 frequency dependence of attenuation. Sediments with greater than 30% sand (by weight), including pure sand, exhibit an f0.5 frequency dependence of attenuation. The measured dispersion is approximately 6% over the frequency range 4–600 kc/sec. Velocity increases with frequency. [Work sponsored by U. S. Navy Bureau of Ships.]