Observations of broadband acoustic backscattering from nonlinear internal waves : assessing the contribution from microstructure
MetadataShow full item record
KeywordAcoustic scattering; Broadband; Nonlinear internal waves; Turbulent oceanic microstructure; Zooplankton
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.
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.
Showing items related by title, author, creator and subject.
Frank, Scott D.; Badiey, Mohsen; Lynch, James F.; Siegmann, William L. (Acoustical Society of America, 2004-12)To investigate acoustic effects of nonlinear internal waves, the two southwest tracks of the SWARM 95 experiment are considered. An airgun source produced broadband acoustic signals while a packet of large nonlinear internal ...
Anisotropy in high-frequency broadband acoustic backscattering in the presence of turbulent microstructure and zooplankton Leong, Doris; Ross, Tetjana; Lavery, Andone C. (Acoustical Society of America, 2012-08)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 ...
Measurements of acoustic scattering from zooplankton and oceanic microstructure using a broadband echosounder Lavery, Andone C.; Chu, Dezhang; Moum, James N. (Oxford University Press, 2009-10-29)In principle, measurements of high-frequency acoustic scattering from oceanic microstructure and zooplankton across a broad range of frequencies can reduce the ambiguities typically associated with the interpretation of ...