Research

19 pages, 3996 KiB

Open AccessArticle

Spatial Coherence Comparisons between the Acoustic Field and Its Frequency-Difference and Frequency-Sum Autoproducts in the Ocean

by Nicholas J. Joslyn, Alexander S. Douglass and David R. Dowling

Acoustics 2022, 4(3), 764-782; https://0-doi-org.brum.beds.ac.uk/10.3390/acoustics4030046 - 07 Sep 2022

Cited by 1 | Viewed by 2414

Abstract

The frequency-difference and frequency-sum autoproducts, quadratic products of complex acoustic field amplitudes at two frequencies, may mimic genuine acoustic fields at the difference and sum frequencies of the constituent fields, respectively. Autoproducts have proven useful in extending the useable frequency range for acoustic [...] Read more.

The frequency-difference and frequency-sum autoproducts, quadratic products of complex acoustic field amplitudes at two frequencies, may mimic genuine acoustic fields at the difference and sum frequencies of the constituent fields, respectively. Autoproducts have proven useful in extending the useable frequency range for acoustic remote sensing to frequencies outside a recorded field’s bandwidth. In array signal processing applications, the spatial coherence of the field often sets performance limits. This paper presents results for the spatial coherence of the genuine field, the frequency-difference autoproduct, and the frequency-sum autoproduct as determined from data collected during the Cascadia Open-Access Seismic Transects (COAST 2012) experiment. In this experiment, an airgun array providing a 10 to 200 Hz signal was repeatedly fired off the coast of Washington state, and the resulting acoustic fields were recorded by a nominal 8 km long, 636-element towed horizontal array. Based on hundreds of airgun firings from a primarily shore-parallel transect, both autoproducts were found to extend field coherence to frequencies outside the genuine field’s bandwidth and to produce longer coherence lengths than genuine fields, in most cases. When used for matched-field processing, the same data illustrate the benefits of the autoproducts’ extended coherence. Full article

(This article belongs to the Special Issue Underwater Acoustics)

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23 pages, 1214 KiB

Open AccessArticle

BDREA Betta and Dolphin Pods Routing via Energy Scarcity Aware Protocol for Underwater Acoustic Wireless Sensor Networks (UAWSNs)

by Hamza Zradgui and Khalil Ibrahimi

Acoustics 2022, 4(3), 656-678; https://0-doi-org.brum.beds.ac.uk/10.3390/acoustics4030040 - 26 Aug 2022

Cited by 1 | Viewed by 1900

Abstract

There exist numerous applications for deploying Underwater Wireless Sensor Networks (UWSNs), including submarine detection, disaster prevention, oil and gas monitoring, off-shore exploration, and military target tracking. The acoustic sensor nodes are deployed to monitor the underwater environment, considering the area under observation. This [...] Read more.

There exist numerous applications for deploying Underwater Wireless Sensor Networks (UWSNs), including submarine detection, disaster prevention, oil and gas monitoring, off-shore exploration, and military target tracking. The acoustic sensor nodes are deployed to monitor the underwater environment, considering the area under observation. This research work proposes an energy scarcity-aware routing protocol for energy efficient UWSNs. Moreover, it aims to find the feasible region on the basis of the objective function, in order to minimize the energy tax and extend the network life. There are three different sensors nodes in the network environment, i.e., anchor nodes, relay nodes, and the centralized station. Anchor nodes originate data packets, while relay nodes process them and broadcast between each other until the packets reach the centralized station. The underline base scheme Weighting Depth and Forwarding Area Division Depth-Based Routing (WDFAD-DBR) for routing is based on the depth differences of the first- and second-hop nodes of the source node. The propose work, Betta and Dolphin Pods Routing via Energy Scarcity Aware protocol (BDREA) for packet forwarding from the forwarding nodes considers the first and second hops of the source node, i.e., the packet advancement, the network traffic, the distance to the centralized station, and the inverse normalized energy of the forwarding zone. It is observed that the proposed work improves the performance parameters by approximately 50% in terms of energy efficiency, and prolongs the network life compared to Dolphin and Whale Pod (DOW-PR) protocols. Furthermore, the energy efficiency directly relates to the other parameters, and its enhancement can be seen in terms of an 18.02% reduction in end-to-end delay when compared with the Weighting Depth and Forwarding Area Division Depth-Based Routing (WDFAD-DBR) protocol. Furthermore, BDREA improves the Packet Delivery Ratio (PDR) by approximately 8.71%, compared to DOW-PR, and by 10% compared with the benchmark, WDFAD-DBR, the energy tax by 50% in comparison to DOW-PR, the end-to-end delay by 18%, and the APD by 5% in comparison to WDFAD-DBR. Full article

(This article belongs to the Special Issue Underwater Acoustics)

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20 pages, 6925 KiB

Open AccessArticle

Investigation of Alberich Coating to Optimise Acoustic Stealth of Submarines

by Callum Daniels and Noel Perera

Acoustics 2022, 4(2), 362-381; https://0-doi-org.brum.beds.ac.uk/10.3390/acoustics4020022 - 11 Apr 2022

Viewed by 3798

Abstract

Due to the nature of their deployment, very few people know the location and course of a submarine during its time at sea, including only a handful of the ship’s crew. The possibility of immediate retaliation by the UK and her allies is [...] Read more.

Due to the nature of their deployment, very few people know the location and course of a submarine during its time at sea, including only a handful of the ship’s crew. The possibility of immediate retaliation by the UK and her allies is aided by the submarine’s ability to remain undetected by SONAR at all times. To investigate one method for improving acoustic stealth, a finite element model (FEM) was created on ANSYS to model a unit-cell of an Alberich coating and impeding sound wave representative of SONAR. A simplification of a widely used acoustic impedance equation was adopted into MATLAB code to attain values of impedance that were applied to the model in place of a water loading boundary. Using the results given by five sets of simulations, an optimised Alberich coating was modelled, containing a 26 mm spherical cavity, 40 mm anechoic layer and 30 mm long steel backplate. This optimised model improved the acoustic stealth of submarines by displaying greater acoustic absorption at both ends of the frequency range, compared with other models used, showing that Alberich-style coatings can be used to improve acoustic stealth, to combat new low-frequency SONAR. Full article

(This article belongs to the Special Issue Underwater Acoustics)

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19 pages, 6047 KiB

Open AccessArticle

Underwater Target Localization Using Opportunistic Ship Noise Recorded on a Compact Hydrophone Array

by Mojgan Mirzaei Hotkani, Jean-Francois Bousquet, Seyed Alireza Seyedin, Bruce Martin and Ehsan Malekshahi

Acoustics 2021, 3(4), 611-629; https://0-doi-org.brum.beds.ac.uk/10.3390/acoustics3040039 - 08 Oct 2021

Cited by 4 | Viewed by 3565

Abstract

In this research, a new application using broadband ship noise as a source-of-opportunity to estimate the scattering field from the underwater targets is reported. For this purpose, a field trial was conducted in collaboration with JASCO Applied Sciences at Duncan’s Cove, Canada in [...] Read more.

In this research, a new application using broadband ship noise as a source-of-opportunity to estimate the scattering field from the underwater targets is reported. For this purpose, a field trial was conducted in collaboration with JASCO Applied Sciences at Duncan’s Cove, Canada in September 2020. A hydrophone array was deployed in the outbound shipping lane at a depth of approximately 71 m to collect broadband noise data from different ship types and effectively localize the underwater targets. In this experiment, a target was installed at a distance (93 m) from the hydrophone array at a depth of 25 m. In this study, a matched field processing (MFP) algorithm is utilized for localization. Different propagation models are presented using Green’s function to generate the replica signal; this includes normal modes in a shallow water waveguide, the Lloyd-mirror pattern for deep water, as well as the image model. We use the MFP algorithm with different types of underwater environment models and a proposed estimator to find the best match between the received signal and the replica signal. Finally, by applying the scatter function on the proposed multi-channel cross correlation coefficient time-frequency localization algorithm, the location of target is detected. Full article

(This article belongs to the Special Issue Underwater Acoustics)

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16 pages, 3665 KiB

Open AccessArticle

Active Control of Submerged Systems by Moving Mass

by Mohammad Yaghoub Abdollahzadeh Jamalabadi

Acoustics 2021, 3(1), 42-57; https://0-doi-org.brum.beds.ac.uk/10.3390/acoustics3010005 - 13 Jan 2021

Cited by 1 | Viewed by 2951

Abstract

In this study, the active vibration control of a rectangular plate submerged in water was investigated. Mass dampers were attached to the plate, and the system was modeled via assumed mode. Water is modeled as an inviscid fluid with moving boundaries at fluid–solid [...] Read more.

In this study, the active vibration control of a rectangular plate submerged in water was investigated. Mass dampers were attached to the plate, and the system was modeled via assumed mode. Water is modeled as an inviscid fluid with moving boundaries at fluid–solid interaction surfaces and applied forces on the plate being calculated by Bernoulli equation. The natural frequencies of the plate in vacuum and in water (for partial and fully submerged cases) found from numerical calculations are compared with experimental results to prove the accuracy of the model. Subsequently, for frequency computations, particular frequencies were chosen and active damping was applied for them. To actively control the plate’s vibration by a moving mass with static stable methods, the displacement data of some points were used as input. First, to increase the damping of target mode at low-frequency, the negative acceleration feedback control algorithm in modal-space was applied. Then, the decentralized method was examined. Both methods were successful in suppressing vibration of the submerged rectangular plate. Full article

(This article belongs to the Special Issue Underwater Acoustics)

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10 pages, 6560 KiB

Open AccessArticle

Application of Waveguide Invariant Theory to Analysis of Interference Phenomenon in Deep Ocean

by Yuan Yao, Chao Sun and Xionghou Liu

Acoustics 2020, 2(3), 595-604; https://0-doi-org.brum.beds.ac.uk/10.3390/acoustics2030031 - 06 Aug 2020

Cited by 2 | Viewed by 3766

Abstract

When a hydrophone is deployed under the critical depth in deep ocean, the interference pattern will be complex and variable. The waveguide invariant is no longer constant and is treated as a distribution. The interference pattern is impacted by refracted and surface reflected [...] Read more.

When a hydrophone is deployed under the critical depth in deep ocean, the interference pattern will be complex and variable. The waveguide invariant is no longer constant and is treated as a distribution. The interference pattern is impacted by refracted and surface reflected (RSR) modes, as well as surface reflected and bottom reflected (SRBR) modes together. This phenomenon is illustrated by numerical simulation and explained by the waveguide invariant theory in this paper. The theory demonstrates: (1) The interference pattern in zone-b corresponds to the waveguide invariant

β_{R S R}

that varies quickly and leads to the slope change, which is contributed by RSR modes whose phase velocity is less than the sound velocity at seafloor; (2) The interference pattern in zone-a1 and zone-c1 is corresponding to the

β_{S R B R W S}

that is the approximately 0.7 and leads to the stable slope, which is contributed by SRBR modes whose phase velocity is between the sound velocity at seafloor and sediment velocity; (3) The interference pattern in zone-a2 and zone-c2 is corresponding to the

β_{S R B R S H}

which hardly varies at low frequency but varies fiercely with source frequency increasing, so the striations are complex with high frequency, which is contributed by SRBR modes whose phase speed is between sediment speed and half space speed. Full article

(This article belongs to the Special Issue Underwater Acoustics)

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17 pages, 3741 KiB

Open AccessArticle

The Use of Soundscapes to Monitor Fish Communities: Meaningful Graphical Representations Differ with Acoustic Environment

by Rita Carriço, Mónica A. Silva, Manuel Vieira, Pedro Afonso, Gui M. Menezes, Paulo J. Fonseca and Maria Clara P. Amorim

Acoustics 2020, 2(2), 382-398; https://0-doi-org.brum.beds.ac.uk/10.3390/acoustics2020022 - 13 Jun 2020

Cited by 5 | Viewed by 4238

Abstract

Many marine animals produce sounds in several phases of their life cycles, either actively or as a byproduct of their activities, such as during mate attraction or when moving. Recent studies of underwater soundscapes have proved passive acoustic monitoring to be a cost-effective, [...] Read more.

Many marine animals produce sounds in several phases of their life cycles, either actively or as a byproduct of their activities, such as during mate attraction or when moving. Recent studies of underwater soundscapes have proved passive acoustic monitoring to be a cost-effective, non-invasive tool to understand ecological processes, especially when sampling in adverse conditions or at great depth. Four days of sound recordings at three seamounts from the Azorean archipelago were examined to assess the suitability of different sound graphical representations to characterize different acoustic environments that contrast in the contribution of vocal fish communities. Long-term spectrograms, sound pressure level, spectral probability densities and the Acoustic Complexity Index (ACI) were computed for two shallow seamounts (Formigas and Princesa Alice, c. 35 m) and one deep seamount (Condor, 190 m) using graphics with different time spans. Only in Formigas, which presented the highest occurrence of fish sounds, was it possible to observe temporal patterns of fish vocal activity in the graphical representations. We highlight that habitats with a higher diversity and abundance of sounds are the most suitable targets for these methods, while in locations with a low prevalence of fish sounds a combination of several methods would be recommended. Full article

(This article belongs to the Special Issue Underwater Acoustics)

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8 pages, 410 KiB

Open AccessCommunication

A Comparison of Optimal SONAR Array Amplitude Shading Coefficients

by Benjamin A. Cray and Ivars Kirsteins

Acoustics 2019, 1(4), 808-815; https://0-doi-org.brum.beds.ac.uk/10.3390/acoustics1040047 - 02 Oct 2019

Cited by 5 | Viewed by 3636

Abstract

This paper compares two different approaches to deriving shading coefficients (weights) for optimal first order and second order directional sensors (that is; sonobuoys, vectors and dyadic sensors). The first approach is an analytical or a physics-based derivation, involving computations with gradients and linearized [...] Read more.

This paper compares two different approaches to deriving shading coefficients (weights) for optimal first order and second order directional sensors (that is; sonobuoys, vectors and dyadic sensors). The first approach is an analytical or a physics-based derivation, involving computations with gradients and linearized momentum; the second is an adaptive minimum variance distortionless response (MVDR) derivation, which finds weights that minimize the cross spectral density (CSD) matrix. The two approaches are shown to be equivalent. In other words, the adaptive MVDR processing procedure does indeed converge to a physics-based solution, without any pre-existing physical knowledge of the behavior of the acoustic field. This suggests that adaptive algorithms innately seek physics-based solutions when these solutions are optimum. The intent of this short communication is not to advocate for one type of adaptive processing method over another. The observation that is presented here is important though, it confirms that at least in an idealized noise field, adaptive processing converges on an optimal set of shading coefficients, similarly derived based on well-established physical acoustics. Full article

(This article belongs to the Special Issue Underwater Acoustics)

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Graphical abstract

19 pages, 1652 KiB

Open AccessArticle

Applicability of Acoustic Concentration Measurements in Suspensions of Artificial and Natural Sediments Using an Acoustic Doppler Velocimeter

by Oliver Chmiel, Ivo Baselt and Andreas Malcherek

Acoustics 2019, 1(1), 59-77; https://0-doi-org.brum.beds.ac.uk/10.3390/acoustics1010006 - 19 Dec 2018

Cited by 12 | Viewed by 4697

Abstract

For the investigation of turbulence and particles, interaction measurement systems are required, which are able to measure velocity and concentration fluctuations simultaneously. Acoustic Doppler Velocimeters (ADV) are widely used for velocity and turbulence measurements in natural and artificial flows. Based on the acoustic [...] Read more.

For the investigation of turbulence and particles, interaction measurement systems are required, which are able to measure velocity and concentration fluctuations simultaneously. Acoustic Doppler Velocimeters (ADV) are widely used for velocity and turbulence measurements in natural and artificial flows. Based on the acoustic sonar theory, a model is presented that correlates the ADV’s Signal-to-Noise Ratio (SNR) and the suspended solids concentration of several natural (Ems Estuary, Lake Eixendorf, Lake Altmühl) and artificial sediments (Chinafill, quartz powder, bentonite, metakaolin) for the range 0.001 g/L–50 g/L. Within the presented method, the sound absorption in water and on particles is considered in a continuous approach for sampling frequencies up to 100 Hz. The widely-used log-linear relation between the SNR and the concentration, which is only valid for low concentrations, was extended for the high concentration regime. Measurement results show a similar behavior of the SNR with respect to varying suspended solid concentrations for different sediments. However, the analysis of the fit parameters shows systematic differences depending on the type of sediment. It is concluded that the proposed model is applicable as well for laboratory use as for measurements in rivers and estuaries. Finally, we discuss the reliability of the results and the methodology with regard to measurements in rivers, lakes, and estuaries. Full article

(This article belongs to the Special Issue Underwater Acoustics)

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