Craig J. Hickey
James M. Sabatier
Natl. Ctr. for Phys. Acoust., Univ. of Mississippi, University, MS 38677
The interpretation of acoustic and seismic measurements in porous materials are usually carried out using the Biot theory. This theory predicts the existence of two P waves (referred to here as type I and type II) and one S wave. The type I P wave is predicted to have small dispersion and attenuation. The type II P wave is predicted to be dispersive and highly attenuating. An experiment is carried out whereby air borne sound is incident upon an air-filled packing of sand. For such a configuration, a large proportion of the transmitted energy is partitioned to the type II P wave. However, due to the high attenuation of the type II P wave this energy should decay rapidly near the surface. Measurements using a probe microphone apparatus, in-situ microphones, and in-situ geophones are obtained in the frequency range of 500--3000 Hz. The in-situ microphones and geophones extend to a depth of 40 cm below the surface in an attempt to detect the Type I P wave. Attenuation and phase velocity of the air-filled packing of sand is determined as a function of depth from these measurements. [Work supported by USDA.]