Feasibility of Ocean Acoustic Waveguide Remote Sensing (OAWRS) of Atlantic Cod with Seafloor Scattering Limitations

• Published in: Remote Sensing
• Main Authors: Ankita D. Jain, Anamaria Ignisca, Dong Hoon Yi, Purnima Ratilal, Nicholas C. Makris
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2013
• Subjects: acoustic remote sensing; wide-area fish detection; OAWRS; waveguide propagation; Atlantic cod; fisheries; seafloor scattering; Science; Q; atlantic cod
• Online Access: https://doi.org/10.3390/rs6010180; https://doaj.org/article/8e9c8a7558cf4b80b1728431d8c862ac

Recently reported declines in the population of Atlantic cod have led to calls for additional survey methods for stock assessments. In combination with conventional line-transect methods that may have ambiguities in sampling fish populations, Ocean Acoustic Waveguide Remote Sensing (OAWRS) has been shown to have a potential for providing accurate stock assessments (Makris N.C., et al. Science 2009, 323, 1,734–1,737; 54th Northeast Regional Stock Assessment Workshop (54th SAW) US Department of Commerce, Northeast Fisheries Science Center, 2012). The use of OAWRS technology enables instantaneous wide-area sensing of fish aggregations over thousands of square kilometers. The ratio of the intensity of scattered returns from fish versus the seafloor in any resolution cell typically determines the maximum fish detection range of OAWRS, which then is a function of fish population density, scattering amplitude and depth distribution, as well as the level of seafloor scattering. With the knowledge of oceanographic parameters, such as bathymetry, sound speed structure and attenuation, we find that a Rayleigh–Born volume scattering approach can be used to efficiently and accurately estimate seafloor scattering over wide areas. From hundreds of OAWRS measurements of seafloor scattering, we determine the Rayleigh–Born scattering amplitude of the seafloor, which we find has a ƒ2,4 frequency dependence below roughly 2 kHz in typical continental shelf environments along the US northeast coast. We then find that it is possible to robustly detect cod aggregations across frequencies at and near swim bladder resonance for observed spawningconfigurations along the U.S. northeast coast, roughly the two octave range 150–600 Hzfor water depths up to roughly 100 m. This frequency range is also optimal for long-rangeocean acoustic waveguide propagation, because it enables multimodal acoustic waveguidepropagation with minimal acoustic absorption and forward scattering losses. As the sensingfrequency moves away from the resonance peak, ...