The relative effect of particles and turbulence on acoustic scattering from deep sea hydrothermal vent plumes revisited.

The relative importance of suspended particles and turbulence as backscattering mechanisms within a hydrothermal plume located on the Endeavour Segment of the Juan de Fuca Ridge is determined by comparing acoustic backscatter measured by the Cabled Observatory Vent Imaging Sonar (COVIS) with model calculations based on in situ samples of particles suspended within the plume. Analysis of plume samples yields estimates of the mass concentration and size distribution of particles, which are used to quantify their contribution to acoustic backscatter. The result shows negligible effects of plume particles on acoustic backscatter within the initial 10-m rise of the plume.

Attenuation of sound in sand sediments due to porosity fluctuations.

At high frequencies, the attenuation measured in sand sediments is larger than that predicted by Biot theory. To account for this discrepancy, perturbation theory is used to incorporate losses due to scattering by porosity variations into both Biot's poroelastic equations and the effective density fluid model. While previous results showed that fluctuations in the bulk frame modulus were insufficient to produce significant attenuation in a sand sediment, modest levels of fluctuations in the porosity produce significant scattering loss.

Application of small-roughness perturbation theory to reverberation in range-dependent waveguides.

A rough-interface reverberation model is developed for range-dependent environments. First-order perturbation theory is employed, and the unperturbed background medium can be layered and heterogeneous with arbitrary range dependence. To calculate the reverberation field, two-way forward scatter due to the slowly changing unperturbed environment is handled by fast numerical methods.

Mid-frequency geoacoustic inversion using bottom loss data from the Shallow Water 2006 Experiment.

Geoacoustic inversion work has typically been carried out at frequencies below 1 kHz, assuming flat, horizontally stratified bottom models. Despite the relevance to Navy sonar systems many of which operate at mid-frequencies (1-10 kHz), limited inversion work has been carried out in this frequency band. This paper is an effort to demonstrate the viability of geoacoustic inversion using bottom loss data between 2 and 5 kHz.

Dispersion and attenuation due to scattering from heterogeneities of the frame bulk modulus of a poroelastic medium.

While Biot theory can successfully account for the dispersion observed in sand sediments, the attenuation at high frequencies has been observed to increase more rapidly than Biot theory would predict. In an effort to account for this additional loss, perturbation theory is applied to Biot's poroelastic equations to model the loss due to the scattering of energy from heterogeneities in the sediment. A general theory for propagation loss is developed and applied to a medium with a randomly varying frame bulk modulus.