© 2003 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Inference of biological and physical parameters in an internal wave using multiple-frequency, acoustic-scattering data
a Woods Hole Oceanographic Institution Woods Hole, MA 02543, USA
b University of North Carolina Chapel Hill, NC 27599, USA
*Correspondence to J. D. Warren, Southampton College, Southampton, NY 11968, USA; tel: +1 631 287 8390; fax: +1 631 287 8419. e-mail: joe.warren{at}liu.edu.
High-frequency sound (>10 kHz) is scattered in the ocean by many different processes. In the water column, marine organisms are often assumed to be the primary source of acoustic backscatter. Recent field experiments and theoretical work suggest that the temperature and salinity microstructure in some oceanic regions could cause acoustic scattering at levels comparable to that caused by marine life. Theoretical acoustic-scattering models predict that the scattering spectra for microstructure and organisms are distinguishable from each other over certain frequency ranges. A method that uses multiple-frequency acoustic data to exploit these differences has been developed, making it possible to discriminate between biological and physical sources of scattering under some conditions. This method has been applied to data collected in an internal wave in the Gulf of Maine. For regions of the internal wave in which the dominant source of scattering is either biological or physical in origin, it is possible to combine the acoustic-scattering data and temperature and salinity profiles with acoustic-scattering models to perform a least-squares inversion. Using this approach, it is possible to estimate the dissipation rate of turbulent kinetic energy for some regions of the internal wave, and the length and numerical abundance of the dominant biological scatterer, euphausiids, in others.
Keywords: acoustics, inverse methods, microstructure, zooplankton
Received 31 July 2002; accepted 31 December 2002.
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