A thesis on high-frequency acoustic volume scattering from marine sediments with application to remote sensing of benthic biological activity is presented. Small perturbation theory is used to describe bistatic volume scattering due to heterogeneity in a sediment modeled as an acoustic fluid half-space. Insight into determining whether single or multiple scattering is significant in the medium is gained by using the bilocal approximation to Dyson's equation. The bilocal approximation for the coherent field is extended to include fluctuation in both the medium density and compressibility. An alternative analysis of multiple scattering is made using exact numerical simulations of two-dimensional volume scattering using the method of moments. Both periodic and nonperiodic random media are considered. Scattering theory is compared with numerical Monte-Carlo simulations and the validity of the small perturbation method is inferred. The effects of the sediment-water interface (half-space) on the scattered field within the sediment and on the bistatic scattering cross-section are investigated.; Benthic biological activity (resulting in bioturbation) creates temporal and spatial variations in the sediment heterogeneity that result in temporal and spatial variations in the sediment volume scattering. This acoustic variability is used as a remote sensing tool to infer parameters of bioturbation. To develop a forward model that relates bioturbation to density fluctuations and therefore to acoustic scattering, a new stochastic model of bioturbation is presented that describes biological mixing as an inhomogeneous (two scale) biodiffusion process. Nonlocal mixing (due to macrofauna) is described as a filtered Poisson process, and local mixing (due to meiofauna) is described as diffusive. Modeling issues such as the spatial stationarity of bioturbation are discussed.; The bioturbation and acoustic scattering models are then combined to produce a model for the decorrelation in time of acoustic backscatter. Model predictions are compared with experimental data collected over a two month period during the Orcas Island experiment. The observed decorrelation of acoustic backscattering from the sediment at the Orcas site is compared to model predictions of temporal decorrelation, and the feasibility of using acoustic remote sensing to detect and study benthic biological activity is discussed.
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