Laboratory and Field Studies of the Acoustics of Multiphase Ocean Bottom Materials

Abstract

Abstract : LONG-TERM GOALS: The long-term scientific objective of this project is to increase our understanding of sound propagation in ocean bottom sediments, including water-saturated sands and muds, gas-bearing sands and muds, and sediments which support seagrass. This in turn benefits buried object detection, sonar operation and acoustic communications in shallow water. The proposed study includes continued analysis of data collected during Shallow Water 06 (SW06), development of apparatus and procedures for propagation and sediment studies for the next planned shallow water experiment (referred to herein as SW12) and continued laboratory studies of the acoustics of the multiphase sediment materials mentioned above. Another goal for the out years is to develop techniques and apparatus for in situ classification of ocean bottoms for Naval fleet operations. OBJECTIVES/APPROACH: The origin of this project was an Entry Level Faculty Award in 2005, then a follow-on grant for 2008 2009. In this time, impedance tube and resonator methods, originally developed by the author for the investigation of bubbly liquids [1, 2], have been successfully modified for the investigation of ocean bottom sediments [3, 4]. In addition, the technique has been applied to the study of gassy sediments [5, 6] and seagrasses [7, 8]. In Refs. [3] through [8], sound speeds have been measured from 100 Hz up to 300 kHz. This work resulted in the author being awarded the 2007 A.B. Wood medal in underwater acoustics [9]. Analysis of SW06 data has also resulted in sound speed and attenuation inferences down to 40 Hz [10]. We now continue the use of these experimental methods to investigate sound propagation in multiphase ocean bottom sediments.