Publication Date:
2022-05-25
Description:
© 2010 The Authors. This article is distributed under the terms of the Creative Commons Attribution-Noncommercial License. The definitive version was published in ICES Journal of Marine Science: Journal du Conseil 67 (2010): 365-378, doi:10.1093/icesjms/fsp262.
Description:
A commercial acoustic system, originally designed for seafloor applications, has been adapted for studying fish with swimbladders. The towed system contains broadband acoustic channels collectively spanning the frequency range 1.7–100 kHz, with some gaps. Using a pulse-compression technique, the range resolution of the echoes is ~20 and 3 cm in the lower and upper ranges of the frequencies, respectively, allowing high-resolution imaging of patches and resolving fish near the seafloor. Measuring the swimbladder resonance at the lower frequencies eliminates major ambiguities normally associated with the interpretation of fish echo data: (i) the resonance frequency can be used to estimate the volume of the swimbladder (inferring the size of fish), and (ii) signals at the lower frequencies do not depend strongly on the orientation of the fish. At-sea studies of Atlantic herring demonstrate the potential for routine measurements of fish size and density, with significant improvements in accuracy over traditional high-frequency narrowband echosounders. The system also detected patches of scatterers, presumably zooplankton, at the higher frequencies. New techniques for quantitative use of broadband systems are presented, including broadband calibration and relating target strength and volume-scattering strength to quantities associated with broadband signal processing.
Description:
The
research was supported by the US Office of Naval Research,
grants number N00014-04-1-0440 and N00014-04-1-0475,
NOAA/CICOR cooperative agreement NA17RJ1223, NOAA/
National Marine Fisheries Service, and the J. Seward Johnson
Chair of the WHOI Academic Programs Office.
Keywords:
Acoustic scattering
;
Broadband
;
Echosounder
;
Fish
;
Resonance
Repository Name:
Woods Hole Open Access Server
Type:
Article
Format:
application/pdf
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