Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 832
Title: Measurements of acoustic scattering from zooplankton and oceanic microstructure using a broadband echosounder
Author: A. C. Lavery, D. Chu, J. Moum
Publication Year: 2010
Journal: ICES Journal of Marine Science
Volume: 67
Issue: 3
Pages: 379-394
Keywords: Broadband acoustic scattering, interval waves, oceanic microstructure, zooplankton
Abstract: 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 acoustic scattering at a single frequency or a limited number of discrete narrowband frequencies. With this motivation, a high-frequency broadband scattering system has been developed for investigating zooplankton and microstructure, involving custom modifications of a commercially available system, with almost complete acoustic coverage spanning the frequency range 150600 kHz. This frequency range spans the Rayleigh-togeometric scattering transition for some zooplankton, as well as the diffusive roll-off in the spectrum for scattering from turbulent temperature microstructure. The system has been used to measure scattering from zooplankton and microstructure in regions of non-linear internal waves. The broadband capabilities of the system provide a continuous frequency response of the scattering over a wide frequency band, and improved range resolution and signal-to-noise ratios through pulse-compression signal-processing techniques. System specifications and calibration procedures are outlined and the system performance is assessed. The results point to the utility of high-frequency broadband scattering techniques in the detection, classification, and under certain circumstances, quantification of zooplankton and microstructure.