Acoustic scattering of broadband echolocation signals from prey of Blainville's beaked whales : modeling and analysis
Jones, Benjamin A.
MetadataShow full item record
Blainville's beaked whales (Mesoplodon densirostris) use broadband, ultrasonic echolocation signals (27 to 57 kHz) to search for, localize, and approach prey that generally consist of mid-water and deep-water fishes and squid. Although it is well known that the spectral characteristics of broadband echoes from marine organisms are a strong function of size, shape, orientation and anatomical group, little is known as to whether or not these or other toothed whales use spectral cues in discriminating between prey and non-prey. In order to study the prey-classification process, a stereo acoustic tag was mounted on a Blainville's beaked whale so that emitted clicks and corresponding echoes from prey could be recorded. A comparison of echoes from prey selected by the whale and those from randomly chosen scatterers suggests that the whale may have, indeed, discriminated between echoes using spectral features and target strengths. Specifically, the whale appears to have favored prey with one or more deep nulls in the echo spectra as well as ones with higher target strength. A three-dimensional, acoustic scattering model is also developed to simulate broadband scattering from squid, a likely prey of the beaked whale. This model applies the distorted wave Born approximation (DWBA) to a weakly-scattering, inhomogeneous body using a combined ray trace and volume integration approach. Scatterer features are represented with volume elements that are small (less than 1/12th of the wavelength) for the frequency range of interest (0 to 120 kHz). Ranges of validity with respect to material properties and numerical considerations are explored using benchmark computations with simpler geometries such as fluid-filled spherical and cylindrical fluid shells. Modeling predictions are compared with published data from live, freely swimming squid. These results, as well as previously published studies, are used in the analysis of the echo spectra of the whale's ensonified targets.
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2006
Showing items related by title, author, creator and subject.
Biomechanics of North Atlantic right whale bone : mandibular fracture as a fatal endpoint for blunt vessel-whale collision modeling Campbell-Malone, Regina (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2007-09)The North Atlantic right whale, Eubalaena glacialis, one of the most critically endangered whales in the world, is subject to high anthropogenic mortality. Vessel-whale collisions and entanglement in fishing gear were ...
Acoustic scattering by axisymmetric finite-length bodies with application to fish : measurement and modeling Reeder, D. Benjamin (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2002-06)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 ...
Acoustic scattering from sand dollars (Dendraster excentricus) : modeling as high aspect ratio oblate objects and comparison to experiment Dietzen, Gregory C. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2008-09)Benthic shells can contribute greatly to the scattering variability of the ocean bottom, particularly at low grazing angles. Among the effects of shell aggregates are increased scattering strength and potential subcritical ...