Instantaneous 3D Continental-Shelf Scale Imaging of Oceanic Fish by Multi-Spectral Resonance Sensing Reveals Group Behavior during Spawning Migration

Yi, Dong Hoon; Gong, Zheng; Jech, J. Michael; Ratilal, Purnima; Makris, Nicholas C.

doi:10.3390/rs10010108

Cited by 11 publications

(17 citation statements)

References 34 publications

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“…The modeled scattering strength SS model of a shoal with mean shoal depth z 0 , shoal thickness H and neutral buoyancy depth z nb at frequency f is calculated [30,31] from SS model (z 0 , H, z nb , n A , f ) = 10 log 10 1 H z 0 +H/2…”

Section: Consistency Between Backscattered Returns and Attenuationmentioning

confidence: 99%

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: Consistency Between Backscattered Returns and Attenuationmentioning

confidence: 99%

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

et al. 2019

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“…The analytic expressions for ν ρ ( ) n s (Eqs. (4), (5) and (6)) and µ ρ τ ( , ) n s (Eqs. (7) and (8)) require the first two statistical moments of the inhomogeneities' scatter function densities.…”

Section: Analytic Expressions For the Mean And Temporal Correlation Omentioning

confidence: 99%

Predicting the Effects of Random Ocean Dynamic Processes on Underwater Acoustic Sensing and Communication

Cho

Makris

2020

Sci Rep

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Acoustics is the primary means of sensing and communication in the ocean for humans and many marine animals. Natural fluctuations in the ocean, however, degrade these abilities in ways that have been previously difficult to forecast. Here, we address this issue by predicting sensing and communication degradation in terms of acoustic attenuation, dispersion and temporal decorrelation at typical operational ranges and frequencies in continental-shelf environments. This is done with analytic expressions derived from first physical principles. The analytic expressions provide the statistics of the acoustic field after forward propagating through an ocean waveguide containing 3-D random inhomogeneities from the independent or combined effects of rough sea-surfaces, nearsea-surface air bubbles and internal waves. The formulation also includes Doppler effects caused by the inhomogeneities' random horizontal motion, enabling modeling and prediction over a wide range of environments and frequencies. Theoretical predictions are confirmed with available acoustic measurements in several continental-shelf environments using standard oceanographic measurements for environmental support. We quantify how the acoustic signals decorrelate over timescales determined by the underlying temporal coherence of ocean dynamic processes. Surface gravity waves and near-sea-surface air bubbles decorrelate acoustic signals over seconds or less, whereas internal waves affect acoustic coherence at timescales of several to tens of minutes. Doppler spread caused by the inhomogeneities' motion further reduces acoustic temporal coherence, and becomes important at the high frequencies necessary for communication and fine-scale sensing. We also show that surface gravity waves and bubbles in high sea states can cause increasingly significant attenuation as frequency increases. The typical durations of marine mammal vocalizations that carry over great distances are found to be consistent with the coherence timescales quantified here and so avoid random distortion of signal information even by incoherent reception. Acoustics is the primary means of sensing and communication in the ocean for applications in such diverse areas as ocean resource management, marine ecology, climatology, oceanography and national defense 1-9. This is due to the severe attenuation of electromagnetic waves in water 3. Current ocean sensing limitations make marine resource management challenging. Without significant improvements in ocean sensing it will be difficult to address the unprecedented decline in many oceanic species recently described and predicted by the United Nations 10. Many marine animals also use acoustics to communicate, navigate, and locate food 11-13. Natural fluctuations and resulting inhomogeneities in the ocean such as surface waves, internal waves and bubbles, however, can significantly degrade acoustic sensing and communication abilities 14-18 by introducing attenuation, dispersion and coherence losses that limit operational ranges, time windows and freq...

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“…Previous OAWRS experiments have revealed the diel shoaling patterns of massive fish groups, including vertical migrations of shoaling herring measured from changes in the resonance frequency of the fish as they move from deep water to their spawning locations [9]. OAWRS also revealed that shoaling fish tend to rapidly congregate in massive groups spanning tens of kilometers when the fish population density reaches a speciesspecific critical value [4].…”

Section: Introductionmentioning

confidence: 99%

Quantification of Wide-Area Norwegian Spring-Spawning Herring Population Density with Ocean Acoustic Waveguide Remote Sensing (OAWRS)

2021

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Norwegian spring-spawning herring are a critical economic resource for multiple nations in the North Atlantic and a keystone species of the Nordic Seas ecosystem. Given the wide areas that the herring occupy, it is difficult to accurately measure the population size and spatial distribution. Ocean Acoustic Waveguide Remote Sensing (OAWRS) was used to instantaneously measure the areal population density of Norwegian herring over more than one thousand square kilometers in spawning grounds near Ålesund, Norway. In the vicinity of the Ålesund trench near peak spawning, significant attenuation in signal-to-noise ratio and mean sensing range was observed after nautical sunset that had not been observed in previous OAWRS surveys in the Nordic Seas or in other regions. We show that this range-dependent decay along a given propagation path was caused by attenuation through dense herring shoals forming at sunset and persisting through the evening for transmissions near the swimbladder resonance peak. OAWRS transmissions are corrected for attenuation in a manner consistent with waveguide scattering theory and simultaneous downward directed local line-transect measurements in the region in order to produce instantaneous wide-area population density maps. Corresponding measured reductions in the median sensing range over the azimuth before ambient noise limitation are shown to be theoretically predictable from waveguide scattering theory and observed population densities. Spatial-temporal inhomogeneities in wide-area herring distributions seen synoptically in OAWRS imagery show that standard sparsely spaced line-transect surveys through this region during spawning can lead to large errors in the estimated population due to spatial and temporal undersampling.

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Instantaneous 3D Continental-Shelf Scale Imaging of Oceanic Fish by Multi-Spectral Resonance Sensing Reveals Group Behavior during Spawning Migration

Cited by 11 publications

References 34 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

Predicting the Effects of Random Ocean Dynamic Processes on Underwater Acoustic Sensing and Communication

Quantification of Wide-Area Norwegian Spring-Spawning Herring Population Density with Ocean Acoustic Waveguide Remote Sensing (OAWRS)

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