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Journal ArticleDOI

Broadband classification and statistics of echoes from aggregations of fish measured by long-range, mid-frequency sonar.

TL;DR: Sparsely distributed, spatially compact fish aggregations were measured in the Gulf of Maine using a long-range broadband sonar using a computationally efficient, physics-based model that accounts for beam-pattern and waveguide effects as well as the scattering response of aggregations of fish.
Abstract: For horizontal-looking sonar systems operating at mid-frequencies (1–10 kHz), scattering by fish with resonant gas-filled swimbladders can dominate seafloor and surface reverberation at long-ranges (i.e., distances much greater than the water depth). This source of scattering, which can be difficult to distinguish from other sources of scattering in the water column or at the boundaries, can add spatio-temporal variability to an already complex acoustic record. Sparsely distributed, spatially compact fish aggregations were measured in the Gulf of Maine using a long-range broadband sonar with continuous spectral coverage from 1.5 to 5 kHz. Observed echoes, that are at least 15 decibels above background levels in the horizontal-looking sonar data, are classified spectrally by the resonance features as due to swimbladder-bearing fish. Contemporaneous multi-frequency echosounder measurements (18, 38, and 120 kHz) and net samples are used in conjunction with physics-based acoustic models to validate this appro...
Citations
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Journal ArticleDOI
TL;DR: It is shown that fish populations in continental shelf environments can be instantaneously imaged over thousands of square kilometers and continuously monitored by a remote sensing technique in which the ocean acts as an acoustic waveguide.
Abstract: Fish populations in continental shelf environments are instantaneously imaged over thousands of square kilometers and continuously monitored by a remote sensing technique in which the ocean acts as an acoustic waveguide [Science 311, 660–663 (2006)]. The technique, ocean acoustic waveguide remote sensing (OAWRS), has revealed the instantaneous horizontal structural characteristics and volatile short‐term behavior of very large fish shoals, containing tens of millions of fish and stretching for many kilometers. The former follows a fractal or power‐law spectral process, indicative of structural similarity at all scales. The latter features compressional waves of fish population density that travel roughly an order of magnitude faster than fish can swim. Here we present an overview of OAWRS imagery documenting fish activity over a 2‐week period in the Spring of 2003 at the edge of the continental shelf, roughly 200 km south of Long Island, NY. Until now, continental shelf environments have been monitored with highly localized line‐transect methods from slow‐moving research vessels. These methods significantly undersample fish populations in time and space, leaving an incomplete and ambiguous record of abundance and behavior.

112 citations

Journal ArticleDOI
TL;DR: This study further substantiates the unique utility of such sonar systems as an ecosystem monitoring tool, and illustrates the importance of considering the impact of the presence of fish on sonar applications.
Abstract: The twilight feeding migration of fish around a shallow water artificial reef (a shipwreck) was observed by a horizontal-looking, mid-frequency sonar The sonar operated at frequencies between 18 and 36 kHz and consisted of a co-located source and horizontal line array deployed at 4 km from the reef The experiment was conducted in a well-mixed shallow water waveguide which is conducive to characterizing fish aggregations at these distances Large aggregations of fish were repeatedly seen to emerge rapidly from the shipwreck at dusk, disperse into the surrounding area during the night, and quickly converge back to the shipwreck at dawn This is a rare, macroscopic observation of an ecologically-important reef fish behavior, delivered at the level of aggregations, instead of individual fish tracks that have been documented previously The significance of this observation on sonar performance associated with target detection in the presence of fish clutter is discussed based on analyses of echo intensity and statistics Building on previous studies of long-range fish echoes, this study further substantiates the unique utility of such sonar systems as an ecosystem monitoring tool, and illustrates the importance of considering the impact of the presence of fish on sonar applications

5 citations


Cites background or methods from "Broadband classification and statis..."

  • ...This parameter combination is identical to those used in Jones et al. (2017)....

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  • ...…interaction of sound with ocean boundaries (sea surface and seafloor) and water column sound speed variabilities can make biological interpretation of echoes from a horizontallooking sonar a challenging task (Gauss et al., 2004; Jones et al., 2014; Jones et al., 2017; Pedersen and Trevorrow, 1999)....

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  • ...…experiments in the late 1960s (e.g., Rusby et al., 1973; Weston and Andrews, 1990; Weston and Revie, 1971), and more recently to image highly dynamic pelagic fish shoals over the scale of a continental shelf (e.g., Gauss et al., 2009; Jones et al., 2017; Makris et al., 2006; Makris et al., 2009)....

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  • ...The heavy tail with non-Rayleigh slope was the result of scattering from a finite number of highlights of the wreck in combination with the strong modulation of echo amplitudes due to highlight positions in the directional sonar beam (Chu and Stanton, 2010; Jones et al., 2017)....

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Journal ArticleDOI
01 Aug 2022
TL;DR: In this paper , the authors examined the potential to classify reef fish based on the fine-scale gas-bearing swim bladder morphology quantified from three-dimensional computed-tomography models.
Abstract: Commercially available broadband echosounders have the potential to classify acoustic targets based on their scattering responses, which are a function of their species-specific morphological and physiological properties. This is particularly important in complex environments with biologically diverse fish assemblages. Using theoretical acoustic scattering models among 130 fishes across six species, we examine the potential to classify reef fish based on the fine-scale gas-bearing swim bladder morphology quantified from three-dimensional computed-tomography models. Modeled echoes of the swim bladder for an incident broadband sound source (30–200 kHz) and across a range of orientation angles (±44°) are acoustically simulated using the boundary element method. Backscatter models present characteristics that are consistent within species and distinguishable among them. Broadband and multifrequency echoes are classified and compared with Bayesian, support vector machine, k-nearest neighbor, and convolutional neural network estimators. Classifiers have higher accuracies (>70%) when noise is not present and perform better when applied to broadband spectra than multifrequency data (42, 70, 100, 132, 160, 184 kHz). The modeling and classification approaches presented indicate that a taxonomic distinction based on morphologically dependent scattering responses is possible and may provide the capacity to acoustically discriminate among fish species.
DOI
TL;DR: In this article, a pattern-analysis-based detection approach was proposed to serve as a warning system for the existence of nearby sea turtles, where the authors focus on the challenge of overcoming the low signal-to-clutter ratio (SCR) caused by reverberations.
Abstract: Abundant in coastal areas, sea turtles are affected by high-intensity acoustic anthropogenic sounds. In this article, we offer a pattern-analysis-based detection approach to serve as a warning system for the existence of nearby sea turtles. We focus on the challenge of overcoming the low signal-to-clutter ratio (SCR) caused by reverberations. Assuming that, owing to low SCR, target reflections within the point cloud are received in groups, our detector searches for patterns through clustering to identify possible “blobs” in the point cloud of reflections, and to classify them as either clutter or a target. Our unsupervised clustering is based on geometrical and spectral constraints over the blob's member relations. In turn, the classification of identified blobs as either a target or clutter is based on features extracted from the reflection pattern. To this end, assuming that reflections from a sea turtle are stable but include spectral diversity due to distortions within the turtle's body, we quantify the stability of the blob's members and the entropy of their reflection spectrum. We test our detector in both the modeled simulations, and at sea, for the detection of sea turtles released after rehabilitation. The results show robustness to highly fluctuating target intensity and ability to detect at low SCR.
Proceedings ArticleDOI
17 Jun 2019
TL;DR: A design for underwater objects identification is suggested using super-resolution beamforming and the distinctions between the low-speed object (such as buoy or low speed AUV) and the beacon can be observed in spatial-temporal spectrum.
Abstract: In underwater environment, the low speed target recognition has been a challenge problem. A design for underwater objects identification is suggested in this paper. The construction can be used in harbor surveillance and ocean environment inspection. Utilizing super-resolution beamforming, the distinctions between the low-speed object (such as buoy or low speed AUV) and the beacon can be observed in spatial-temporal spectrum. Corresponding to the features of power differences and spatial spectrum variance in vertical direction, the low-speed object can be separated from beacon. The data from lake experiment is dealt with and illustrate the method.

Cites methods from "Broadband classification and statis..."

  • ...In [5], fish aggregations classification was investigated for horizontal-looking sonar at mid-frequencies (1-10kHz), based on the properties including swimbladder and density....

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References
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Journal ArticleDOI
TL;DR: In this article, a split-step Pade solution for the parabolic equation (PE) method is derived for problems involving very wide propagation angles, large depth variations in the properties of the waveguide, and elastic ocean bottoms.
Abstract: A split‐step Pade solution is derived for the parabolic equation (PE) method. Higher‐order Pade approximations are used to reduce both numerical errors and asymptotic errors (e.g., phase errors due to wide‐angle propagation). This approach is approximately two orders of magnitude faster than solutions based on Pade approximations that account for asymptotic errors but not numerical errors. In contrast to the split‐step Fourier solution, which achieves similar efficiency for some problems, the split‐step Pade solution is valid for problems involving very wide propagation angles, large depth variations in the properties of the waveguide, and elastic ocean bottoms. The split‐step Pade solution is practical for global‐scale problems.

682 citations

Journal ArticleDOI
27 Mar 2009-Science
TL;DR: By quantifying the formation processes of vast oceanic fish shoals during spawning, it is shown that a rapid transition from disordered to highly synchronized behavior occurs as population density reaches a critical value and general theoretical predictions believed to apply in nature irrespective of animal species are confirmed.
Abstract: Similarities in the behavior of diverse animal species that form large groups have motivated attempts to establish general principles governing animal group behavior. It has been difficult, however, to make quantitative measurements of the temporal and spatial behavior of extensive animal groups in the wild, such as bird flocks, fish shoals, and locust swarms. By quantifying the formation processes of vast oceanic fish shoals during spawning, we show that (i) a rapid transition from disordered to highly synchronized behavior occurs as population density reaches a critical value; (ii) organized group migration occurs after this transition; and (iii) small sets of leaders significantly influence the actions of much larger groups. Each of these findings confirms general theoretical predictions believed to apply in nature irrespective of animal species.

200 citations

Journal ArticleDOI
03 Feb 2006-Science
Abstract: Until now, continental shelf environments have been monitored with highly localized line-transect methods from slow-moving research vessels. These methods significantly undersample fish populations in time and space, leaving an incomplete and ambiguous record of abundance and behavior. We show that fish populations in continental shelf environments can be instantaneously imaged over thousands of square kilometers and continuously monitored by a remote sensing technique in which the ocean acts as an acoustic waveguide. The technique has revealed the instantaneous horizontal structural characteristics and volatile short-term behavior of very large fish shoals, containing tens of millions of fish and stretching for many kilometers.

198 citations

Journal ArticleDOI
TL;DR: The mean TS of herring was found to be significantly dependent on the depth (pressure) and the gonadosomatic index, which are the additional parameters included in the new TS relationship.
Abstract: Target-strength (TS) experiments on captive, adult herring have been conducted at intervals over several years to investigate the acoustic effect of pressure and seasonal changes on fish physiology. Experiments in a large, net pen (4500 m 3 ) were done at 18, 38, and 120 kHz frequencies with calibrated, split-beam echosounders. The main ex situ results at 38 kHz, including a vertical-excursion experiment, were combined with in situ TS data collected at 38 kHz with a probing, split-beam transducer lowered into the dense herring layers, recorded during two surveys in the wintering area of the Norwegian spring-spawning stock. Multiple-linear regression analysis was used to investigate the functional relationship between TS and the measured parameters. The mean TS of herring was found to be significantly dependent on the depth (pressure) and the gonadosomatic index. These are the additional parameters included in the new TS relationship.

145 citations

Journal ArticleDOI
TL;DR: In this article, an efficient method is presented to numerically simulate stochastic internal-wave-induced sound-speed perturbation fields in deep ocean environments, where the sound speed perturbations are represented as an internal wave eigenfunction expansion in which WKB amplitude scaling and stretching of the depth coordinate are exploited.
Abstract: An efficient method is presented to numerically simulate stochastic internal-wave-induced sound-speed perturbation fields in deep ocean environments. The sound-speed perturbation field is represented as an internal-wave eigenfunction expansion in which WKB amplitude scaling and stretching of the depth coordinate are exploited. Individual realizations of the sound-speed perturbation field are constructed by evaluating a multidimensional fast Fourier transform of a complex-valued function whose modulus has a known simple form and whose phase is random. Approximations made are shown to be consistent with approximations built into the Garrett–Munk internal-wave spectrum, which is the starting point of this analysis. Both time-varying internal-wave fields in three space dimensions and frozen fields in a vertical plane are considered.

139 citations