Target strength distributions of Pacific sardine schools: Model results at 500 Hz to 10 kHz

Love, Richard H.; Fialkowski, Joseph M.; Jagielo, Thomas H.

doi:10.1121/1.4966553

Cited by 4 publications

(3 citation statements)

References 28 publications

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“…These have traditionally been employed in the analysis of fisheries acoustic data where attenuation due to dense fish groups has been studied [18][19][20][21][22][23]. While free space formulations for attenuation from fish are valid for downward directed echosounders, we find that common heuristic approaches that employ free space scattering assumptions for attenuation from fish groups in long-range waveguide propagation can lead to significant errors [24][25][26].…”

Section: Introductionmentioning

confidence: 94%

The Effect of Attenuation from Fish Shoals on Long-Range, Wide-Area Acoustic Sensing in the Ocean

et al. 2019

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Acoustics is the primary means of long-range and wide-area sensing in the ocean due to the severe attenuation of electromagnetic waves in seawater. While it is known that densely packed fish groups can attenuate acoustic signals during long-range propagation in an ocean waveguide, previous experimental demonstrations have been restricted to single line transect measurements of either transmission or backscatter and have not directly investigated wide-area sensing and communication issues. Here we experimentally show with wide-area sensing over 360 • in the horizontal and ranges spanning many tens of kilometers that a single large fish shoal can significantly occlude acoustic sensing over entire sectors spanning more than 30 • with corresponding decreases in detection ranges by roughly an order of magnitude. Such blockages can comprise significant impediments to underwater acoustic remote sensing and surveillance of underwater vehicles, marine life and geophysical phenomena as well as underwater communication. This makes it important to understand the relevant mechanisms and accurately predict attenuation from fish in long-range underwater acoustic sensing and communication. To do so, we apply an analytical theory derived from first principles for acoustic propagation and scattering through inhomogeneities in an ocean waveguide to model propagation through fish shoals. In previous experiments, either the attenuation from fish in the shoal or the scattering cross sections of fish in the shoal were measured but not both, making it impossible to directly confirm a theoretical prediction on attenuation through the shoal. Here, both measurements have been made and they experimentally confirm the waveguide theory presented. We find experimentally and theoretically that attenuation can be significant when the sensing frequency is near the resonance frequency of the shoaling fish. Negligible attenuation was observed in previous low-frequency ocean acoustic waveguide remote sensing (OAWRS) experiments because the sensing frequency was sufficiently far from the swimbladder resonance peak of the shoaling fish or the packing densities of the fish shoals were not sufficiently high. We show that common heuristic approaches that employ free space scattering assumptions for attenuation from fish groups can lead to significant errors for applications involving long-range waveguide propagation and scattering.

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Section: Introductionmentioning

confidence: 94%

The Effect of Attenuation from Fish Shoals on Long-Range, Wide-Area Acoustic Sensing in the Ocean

et al. 2019

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“…These have traditionally been employed in the analysis of fisheries acoustic data where attenuation due to dense fish groups has been studied [11,46,17,49,3,63]. While free space formulations for attenuation from fish are valid for downward directed echosounders, we find that common heuristic approaches that employ free space scattering assumptions for attenuation from fish groups in long-range waveguide propagation can lead to significant errors [59,13,32].…”

Section: Introductionmentioning

confidence: 95%

“…While some of these experiments included synoptic echosounder measurements of fish density and vertical distribution [12,13], they did not include direct observations of the fish groups occluding the propagation path. A later study predicted that attenuation from sardine shoals off the west coast of the United States would be significant using measurements of shoal size and population density, but the study did not include experimental measurements of acoustic attenuation to compare with predictions [32]. Here, OAWRS is used to instantaneously image fish shoals that stretch for thousands of square kilometers and simultaneously measure attenuation from these shoals within the active OAWRS transmissions, as well as attenuation to ship-radiated tonals detected by Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS).…”

Section: -4mentioning

confidence: 99%

The effect of attenuation from fish on long-range active and passive acoustic sensing in the ocean

Duane¹

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Attenuation from fish can reduce the intensity of acoustic signals and significantly decrease detection range for long-range active and passive sensing in the ocean. This makes it important to understand the relevant mechanisms and accurately predict attenuation from fish in underwater acoustic sensing. Formulations for predicting attenuation from fish, however, depend on the accurate characterization of population density and spatial distribution of fish groups along long-range propagation paths, which is difficult to achieve using conventional survey methods. In previous investigations of attenuation from fish, population densities were inferred from reductions in the intensity of long-range acoustic signals caused by diel or seasonal shoaling patterns of fish groups. Here, Ocean Acoustic Waveguide Remote Sensing (OAWRS) is used to instantaneously image massive Norwegian herring shoals that stretch for thousands of square kilometers and simultaneously measure attenuation from these shoals within the active OAWRS transmissions, as well as attenuation to ship-radiated tonals detected by Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS). Reductions in signal intensity are predicted using a normal-mode-based analytical theory derived from first principles for acoustic propagation and scattering through inhomogeneities in an ocean waveguide. The predictions of the waveguide attenuation formulation are in agreement with measured reductions from attenuation, where the position, size, and population density of the fish groups are characterized using OAWRS imagery as well as in situ echosounder measurements of the specific shoals occluding the propagation path. Common heuristic formulations that employ free space scattering assumptions for attenuation from fish groups are not in agreement with measurements here, and waveguide scattering theory is found to be necessary for accurate predictions. It is experimentally and theoretically shown that attenuation can be significant when the sensing frequency is near the resonance frequency of the shoaling fish, where scattering losses from the fish swimbladders and damping from fish flesh is most significant. Negligible attenuation was observed in previous OAWRS and POAWRS surveys because the frequency of the acoustic signals was sufficiently far from the swimbladder resonance peak of the shoaling fish or the packing densities of the fish shoals were not sufficiently high.

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Computing bias and variance for Pacific sardine (Sardinops sagax) biomass estimated from aerial surveys in California nearshore waters

Dorval,

Lynn,

Porzio

et al. 2024

Fisheries Research

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Target strength distributions of Pacific sardine schools: Model results at 500 Hz to 10 kHz

Cited by 4 publications

References 28 publications

The Effect of Attenuation from Fish Shoals on Long-Range, Wide-Area Acoustic Sensing in the Ocean

The Effect of Attenuation from Fish Shoals on Long-Range, Wide-Area Acoustic Sensing in the Ocean

The effect of attenuation from fish on long-range active and passive acoustic sensing in the ocean

Computing bias and variance for Pacific sardine (Sardinops sagax) biomass estimated from aerial surveys in California nearshore waters

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