Acoustical Study Of Fluid Mud

Abstract

Laboratory and field experiments were performed to investigate fluid mud properties by acoustic reflection technique using 192 KHz and 1.0 MHz transceivers. with the return signals sampled at 30 KHz and digitized with 12 bit resolution. Lab- oratory experiments were carried out in a cylindrical tank using sample of fluid mud collected from the Chesapeake Bay; field experiments were carried out in Battery Park, Delaware Bay and included in situ acoustic measurements as well as collection of bottom samples using a modified gravity corer. Acoustic measurements were taken in the laboratory on the simulated fluid mud to determine the relationship between bulk density and acoustic backscatter- ing, by allowing the fluid mud to settle. Laboratory measurements shows that sound attenuation was increased as a result of fluid mud compaction, approximately about 28 dB/m for the 192 KHz and 120 dB/m for the 1.0 MHz at the end of the compaction experiments (fluid mud thickness: 15 cm). The frequency depen- dance attenuation (f") of fluid mud is also increased as fluid mud compacted: at the end of compaction, the power value obtained was 0.9. Bulk density obtained and its corresponding acoustic backscattering show no clear relationship as a result of cancellation effect between bulk density (p) and sound speed (c).