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Observations of broadband acoustic backscattering from nonlinear internal waves : assessing the contribution from microstructure

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dc.contributor.author Lavery, Andone C.
dc.contributor.author Chu, Dezhang
dc.contributor.author Moum, James N.
dc.date.accessioned 2011-01-07T17:14:11Z
dc.date.available 2011-01-07T17:14:11Z
dc.date.issued 2010-11-30
dc.identifier.citation IEEE Journal of Oceanic Engineering 35 (2010): 695-709 en_US
dc.identifier.uri http://hdl.handle.net/1912/4295
dc.description Author Posting. © IEEE, 2010. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 35 (2010): 695-709, doi:10.1109/JOE.2010.2047814. en_US
dc.description.abstract In this paper, measurements of high-frequency broadband (160-590 kHz) acoustic backscattering from surface trapped nonlinear internal waves of depression are presented. These waves are ideal for assessing the contribution from oceanic microstructure to scattering as they are intensely turbulent. Almost coincident direct microstructure measurements were performed and zooplankton community structure was characterized using depth-resolved net sampling techniques. The contribution to scattering from microstructure can be difficult to distinguish from the contribution to scattering from zooplankton using a single narrowband frequency as microstructure and zooplankton are often colocated and can have similar scattering levels over a range of frequencies. Yet their spectra are distinct over a sufficiently broad frequency range, allowing broadband backscattering measurements to reduce the ambiguities typically associated with the interpretation of narrowband measurements. In addition, pulse compression signal processing techniques result in very high-resolution images, allowing physical processes that are otherwise hard to resolve to be imaged, such as Kelvin-Helmholtz shear instabilities. In this study, high-resolution acoustic observations of multiple nonlinear internal waves are presented and regions with distinct scattering spectra are identified. Spectra that decrease in level across the available frequency band were highly correlated to regions of intense turbulence and high stratification, and to Kevin-Helmholtz shear instabilities in particular. Spectra that increase in level across the available frequency band were consistent with scattering dominated by small zooplankton. Simple inversions for relevant microstructure parameters are presented. Limitations of, and improvements to, the broadband system and techniques utilized in this study are discussed. en_US
dc.description.sponsorship This work was supported in part by the Woods Hole Oceanographic Institution and the U.S. Office of Naval Research under Grant N000140210359. en_US
dc.format.mimetype application/pdf
dc.language.iso en_US en_US
dc.publisher IEEE en_US
dc.relation.uri http://dx.doi.org/10.1109/JOE.2010.2047814
dc.subject Acoustic scattering en_US
dc.subject Broadband en_US
dc.subject Nonlinear internal waves en_US
dc.subject Turbulent oceanic microstructure en_US
dc.subject Zooplankton en_US
dc.title Observations of broadband acoustic backscattering from nonlinear internal waves : assessing the contribution from microstructure en_US
dc.type Article en_US
dc.identifier.doi 10.1109/JOE.2010.2047814


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