Anisotropy in high-frequency broadband acoustic backscattering in the presence of turbulent microstructure and zooplankton
Lavery, Andone C.
MetadataShow full item record
High-frequency broadband (120–600 kHz) acoustic backscattering measurements have been made in the vicinity of energetic internal waves. The transducers on the backscattering system could be adjusted so as to insonify the water-column either vertically or horizontally. The broadband capabilities of the system allowed spectral classification of the backscattering. The distribution of spectral shapes is significantly different for scattering measurements made with the transducers oriented horizontally versus vertically, indicating that scattering anisotropy is present. However, the scattering anisotropy could not be unequivocally explained by either turbulent microstructure or zooplankton, the two primary sources of scattering expected in internal waves. Daytime net samples indicate a predominance of short-aspect-ratio zooplankton. Using zooplankton acoustic scattering models, a preferential orientation of the observed zooplankton cannot explain the measured anisotropy. Yet model predictions of scattering from anisotropic turbulent microstructure, with inputs from coincident microstructure measurements, were not consistent with the observations. Possible explanations include bandwidth limitations that result in many spectra that cannot be unambiguously attributed to turbulence or zooplankton based on spectral shape. Extending the acoustic bandwidth to cover the range from 50 kHz to 2 MHz could help improve identification of the dominant sources of backscattering anisotropy.
Author Posting. © Acoustical Society of America, 2012. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 132 (2012): 670-679, doi:10.1121/1.4730904.
Showing items related by title, author, creator and subject.
Stephen, Ralph A.; Bolmer, S. Thompson; Udovydchenkov, Ilya A.; Worcester, Peter F.; Dzieciuch, Matthew A.; Andrew, Rex K.; Mercer, James A.; Colosi, John A.; Howe, Bruce M. (Acoustical Society of America, 2013-10)Ocean bottom seismometer observations at 5000 m depth during the long-range ocean acoustic propagation experiment in the North Pacific in 2004 show robust, coherent, late arrivals that are not readily explained by ocean ...
Foote, Kenneth G.; Hastings, Mardi C.; Ketten, Darlene R.; Lin, Ying-Tsong; Reidenberg, Joy S.; Rye, Kent (Acoustical Society of America, 2012-02)Potential physical effects of sonar transmissions on marine mammals were investigated by measuring pressure fields induced in a 119-kg, 211-cm-long, young adult male common dolphin (Delphinus delphis) cadaver. The specimen ...
Observationally constrained modeling of sound in curved ocean internal waves: Examination of deep ducting and surface ducting at short range Duda, Timothy F.; Lin, Ying-Tsong; Reeder, D. Benjamin (Acoustical Society of America, 2011-09)A study of 400 Hz sound focusing and ducting effects in a packet of curved nonlinear internal waves in shallow water is presented. Sound propagation roughly along the crests of the waves is simulated with a three-dimensional ...