Acoustic scattering by axisymmetric finite-length bodies with application to fish : measurement and modeling
Acoustic scattering by axisymmetric finite-length bodies with application to fish : measurement and modeling
Date
2002-06
Authors
Reeder, D. Benjamin
Linked Authors
Person
Alternative Title
Citable URI
As Published
Date Created
Location
DOI
10.1575/1912/2587
Related Materials
Replaces
Replaced By
Keywords
Underwater acoustics
Abstract
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 effcient for a wide range of frequencies, angles of orientation,
irregular axisymmetric shapes and boundary conditions. The model presented is an extension of
a two-dimensional conformal mapping approach to scattering by irregular, finite-length bodies
of revolution. An extensive series of broadband acoustic backscattering measurements has been
conducted involving alewife fish (Alosa pseudoharengus), which are morphologically similar to
the Atlantic herring (Clupea harengus). A greater-than-octave bandwidth (40-95 kHz), shaped,
linearly swept, frequency modulated signal was used to insonify live, adult alewife that were
tethered while being rotated in 1-degree increments over all angles of orientation 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 include very highresolution
Phase Contrast X-rays (PCX) and Computerized Tomography (CT) scans, which 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.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2002
Embargo Date
Citation
Reeder, D. B. (2002). Acoustic scattering by axisymmetric finite-length bodies with application to fish : measurement and modeling [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server. https://doi.org/10.1575/1912/2587