Acoustic Scattering by Axisymmetric Finite-length Bodies with Application to Fish: Measurement and Modeling

D. Benjamin Reeder, Ph.D., 2002
Timothy Stanton, Advisor

This thesis investigates the complexities of acoustic scattering by finite bodies in general and by fish in particular through the development of an advanced acoustic scattering model and detailed laboratory acoustic measurements. A general acoustic scattering model is developed that is accurate and numerically efficient for a wide range of frequencies, angles of orientation, irregular axisymmetric shapes and boundary conditions. An extensive series of broadband acoustic backscattering measurements has been conducted involving alewife fish (Alosa pseudoharengus). A broadband (40-95 kHz) chirp was used to insonify live, adult alewife that were tethered while being rotated in 1-degree increments over all angles in two planes of rotation (lateral and dorsal/ventral). Spectral analysis correlates frequency dependencies to morphology and orientation. Pulse compression processing temporally resolves multiple returns from each individual which show good correlation with size and orientation, and demonstrate that there exists more than one significant scattering feature in the animal. Imaging technologies used to exactly measure the morphology of the scattering features of fish are used for morphological evaluation and incorporation into the scattering model. Studies such as this one, which combine scattering models with high-resolution morphological information and high-quality laboratory data, are crucial to the quantitative use of acoustics in the ocean.

D. Benjamin Reeder, Ph.D., 2002
Timothy Stanton, Advisor