The Effect of Attenuation from Fish on Passive Detection of Sound Sources in Ocean Waveguide Environments

Attenuation from fish can reduce the intensity of acoustic signals and significantly decrease detection range for long-range passive sensing of manmade vehicles, geophysical phenomena, and vocalizing marine life. The effect of attenuation from herring shoals on the Passive Ocean Acoustic Waveguide Remote Sensing (POAWRS) of surface vessels is investigated here, where concurrent wide-area active Ocean Acoustic Waveguide Remote Sensing (OAWRS) is used to confirm that herring shoals occluding the propagation path are responsible for measured reductions in ship radiated sound and corresponding detection losses. Reductions in the intensity of ship-radiated sound are predicted using a formulation for acoustic attenuation through inhomogeneities in an ocean waveguide that has been previously shown to be consistent with experimental measurements of attenuation from fish in active OAWRS transmissions. 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. Experimental measurements of attenuation presented here confirm previous theoretical predictions that common heuristic formulations employing free space scattering assumptions can be in significant error. Waveguide scattering and propagation theory is found to be necessary for accurate predictions.

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

Remote Sensing ◽

10.3390/rs13224546 ◽

2021 ◽

Vol 13 (22) ◽

pp. 4546

Author(s):

Daniel Duane ◽

Olav Rune Godø ◽

Nicholas C. Makris

Keyword(s):

Remote Sensing ◽

Population Density ◽

Scattering Theory ◽

Wide Area ◽

Propagation Path ◽

Line Transect ◽

Economic Resource ◽

Nordic Seas ◽

Acoustic Waveguide ◽

Sensing Range

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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Optical Analysis of Ball Bearing Starvation

Journal of Lubrication Technology ◽

10.1115/1.3451591 ◽

1971 ◽

Vol 93 (3) ◽

pp. 349-361 ◽

Cited By ~ 172

Author(s):

L. D. Wedeven ◽

D. Evans ◽

A. Cameron

Keyword(s):

Film Thickness ◽

Ball Bearing ◽

Point Contact ◽

Experimental Measurements ◽

Line Contact ◽

Optical Analysis ◽

Grease Lubrication ◽

Theoretical Predictions ◽

Pressure Stress ◽

Starvation Conditions

Elastohydrodynamic oil film measurements for rolling point contact under starvation conditions are obtained using optical interferometry. The experimental measurements present a reasonably clear picture of the starvation phenomenon and are shown to agree with theoretical predictions. Starvation inhibits the generation of pressure and, therefore, reduces film thickness. It also causes the overall pressure, stress, and elastic deformation to become more Hertzian. Additional experiments using interferometry illustrate: the cavitation pattern, lubricant entrapment, grease lubrication, ball spin, and edge effects in line contact.

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Bioinspired aerofoil adaptations: the next steps for theoretical models

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2019.0070 ◽

2019 ◽

Vol 377 (2159) ◽

pp. 20190070 ◽

Cited By ~ 3

Author(s):

Lorna J. Ayton

Keyword(s):

Experimental Data ◽

Theoretical Models ◽

Theoretical Modelling ◽

Experimental Measurements ◽

Far Field ◽

Acoustic Analogy ◽

Trailing Edge ◽

Trailing Edge Noise ◽

Theoretical Predictions ◽

Field Noise

The extended introduction in this paper reviews the theoretical modelling of leading- and trailing-edge noise, various bioinspired aerofoil adaptations to both the leading and trailing edges of blades, and how these adaptations aid in the reduction of aerofoil–turbulence interaction noise. Attention is given to the agreement between current theoretical predictions and experimental measurements, in particular, for turbulent interactions at the trailing edge of an aerofoil. Where there is a poor agreement between theoretical models and experimental data the features neglected from the theoretical models are discussed. Notably, it is known that theoretical predictions for porous trailing-edge adaptations do not agree well with experimental measurements. Previous works propose the reason for this: theoretical models do not account for surface roughness due to the porous material and thus omit a key noise source. The remainder of this paper, therefore, presents an analytical model, based upon the acoustic analogy, to predict the far-field noise due to a rough surface at the trailing edge of an aerofoil. Unlike previous roughness noise models which focus on roughness over an infinite wall, the model presented here includes diffraction by a sharp edge. The new results are seen to be in better agreement with experimental data than previous models which neglect diffraction by an edge. This new model could then be used to improve theoretical predictions for far-field noise generated by turbulent interactions with a (rough) porous trailing edge. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.

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The overlapping roles of the inner ear and lateral line: the active space of dipole source detection

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2000.0650 ◽

2000 ◽

Vol 355 (1401) ◽

pp. 1115-1119 ◽

Cited By ~ 25

Author(s):

Christopher B. Braun ◽

Sheryl Coombs

Keyword(s):

Inner Ear ◽

Lateral Line ◽

Near Field ◽

Dipole Source ◽

Source Detection ◽

Sound Sources ◽

Distance Range ◽

Spatial Gradients ◽

Theoretical Predictions ◽

Benthic Fishes

The problems associated with the detection of sounds and other mechanical disturbances in the aquatic environment differ greatly from those associated with airborne sounds. The differences are primarily due to the incompressibility of water and the corresponding increase in importance of the acoustic near field. The near field, or hydrodynamic field, is characterized by steep spatial gradients in pressure, and detection of the accelerations associated with these gradients is performed by both the inner ear and the lateral line systems of fishes. Acceleration–sensitive otolithic organs are present in all fishes and provide these animals with a form of inertial audition. The detection of pressure gradients, by both the lateral line and inner ear, is the taxonomically most widespread mechanism of sound–source detection amongst vertebrates, and is thus the most likely primitive mode of detecting sound sources. Surprisingly, little is known about the capabilities of either the lateral line or the otolithic endorgan in the detection of vibratory dipole sources. Theoretical considerations for the overlapping roles of the inner ear and lateral line systems in midwater predict that the lateral line will operate over a shorter distance range than the inner ear, although with a much greater spatial resolution. Our empirical results of dipole detection by mottled sculpin, a benthic fish, do not agree with theoretical predictions based on midwater fishes, in that the distance ranges of the two systems appear to be approximately equal. This is almost certainly as a result of physical coupling between the fishes and the substrate. Thus, rather than having a greater active range, the inner ear appears to have a reduced distance range in benthic fishes, and the lateral line distance range may be concomitantly extended.

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Effect of multiple scattering and modal dispersion on population density imagery of Atlantic herring shoals with ocean acoustic waveguide remote sensing.

The Journal of the Acoustical Society of America ◽

10.1121/1.3249397 ◽

2009 ◽

Vol 126 (4) ◽

pp. 2293

Author(s):

Mark Andrews

Keyword(s):

Remote Sensing ◽

Population Density ◽

Multiple Scattering ◽

Atlantic Herring ◽

Acoustic Waveguide ◽

Modal Dispersion

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Effects of multiple scattering, attenuation, and dispersion on fish population density imaging with ocean‐acoustic waveguide remote sensing.

The Journal of the Acoustical Society of America ◽

10.1121/1.3507978 ◽

2010 ◽

Vol 128 (4) ◽

pp. 2279-2279

Author(s):

Mark Andrews ◽

Zheng Gong ◽

Purnima Ratilal

Keyword(s):

Remote Sensing ◽

Population Density ◽

Multiple Scattering ◽

Fish Population ◽

Acoustic Waveguide ◽

Scattering Attenuation ◽

Attenuation And Dispersion

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Analytic Calculations of the Branching Ratio and CP Violation in Bs0 → Ds+Ds− Decay

Modern Physics Letters A ◽

10.1142/s0217732320501229 ◽

2020 ◽

Vol 35 (15) ◽

pp. 2050122

Author(s):

H. R. Khan ◽

E. H. Raslan ◽

R. A. Reem

Keyword(s):

Cp Violation ◽

Decay Width ◽

Branching Ratio ◽

Gluon Condensate ◽

Analytic Calculation ◽

Experimental Measurements ◽

Meson Decays ◽

First Order ◽

Theoretical Predictions ◽

Charge Parity

We present an analytic calculation of Branching Ratio (BR) and Charge-Parity (CP) violating asymmetries of the [Formula: see text] meson decays to [Formula: see text] by calculating the amplitude and the decay width of the process including the chiral loop and gluon condensate to first-order. We find the BR of [Formula: see text] which is in agreement with other experimental measurements and theoretical predictions. We also calculate the direct CP violation, CP violation in mixing and CP violation due to interference which are [Formula: see text], [Formula: see text] and [Formula: see text], respectively.

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