Investigation of the Acoustics of Marine Sediments Using an Impedance Tube

The primary objective is to obtain experimental measurements of the plane wave reflection coefficients from laboratory and in situ sediments using impedance tube [1] and acoustic resonator tube [2, 3] methods, in the frequency range of approximately 300 Hz to tens of kHz. This approach will also yield measurements of the acoustic impedance, sediment sound speed, attenuation, and complex density through the use of appropriate model inversions and data analysis. These measurements will span a frequency range in which there is little experimental data and help to verify competing theoretical models [4-11] on sound propagation in marine sediments. An overview of the state-of-the-art in both experiment and modeling is shown in Fig. 1. Note the lack of data below a few kHz and the inability of a single model to correctly describe both the sound speed and the attenuation. Initial impedance tube work [12] indicated that the coupling between the sediment and the impedance tube walls must be accounted for, in order to infer the intrinsic sediment attenuation from measurements performed in an impedance tube. Therefore, an initial objective was to develop an appropriate model that describes this coupling, and to develop a new impedance tube that exploits this model, i.e. minimizes the coupling, and allows for accurate recovery of intrinsic sediment attenuation from the measurements.