Research

17 pages, 516 KiB

Open AccessArticle

Random Matrix Theory for Sound Propagation in a Shallow-Water Acoustic Waveguide with Sea Bottom Roughness

by Denis V. Makarov, Pavel S. Petrov and Michael Yu. Uleysky

J. Mar. Sci. Eng. 2023, 11(10), 1987; https://doi.org/10.3390/jmse11101987 - 14 Oct 2023

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The problem of sound propagation in a shallow sea with a rough sea bottom is considered. A random matrix approach for studying sound scattering by the water–bottom interface inhomogeneities is developed. This approach is based on the construction of a statistical ensemble of [...] Read more.

The problem of sound propagation in a shallow sea with a rough sea bottom is considered. A random matrix approach for studying sound scattering by the water–bottom interface inhomogeneities is developed. This approach is based on the construction of a statistical ensemble of the propagator matrices that describe the evolution of the wavefield in the basis of normal modes. A formula for the coupling term corresponding to inter-mode transitions due to scattering by the sea bottom is derived. The Weisskopf–Wigner approximation is utilized for the coupling between waterborne and sediment modes. A model of a waveguide with the bottom roughness described by the stochastic Ornstein–Uhlenbeck process is considered as an example. Range dependencies of mode energies, modal cross coherences and scintillation indices are computed using Monte Carlo simulations. It is shown that decreasing the roughness correlation length enhances mode coupling and facilitates sound scattering. Full article

(This article belongs to the Special Issue Sound Scattering in the Ocean)

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14 pages, 363 KiB

Open AccessArticle

Formal Derivations of Mode Coupling Equations in Underwater Acoustics: How the Method of Multiple Scales Results in an Expansion over Eigenfunctions and the Vectorized WKBJ Solution for the Amplitudes

by Mikhail Trofimov, Sergey Kozitskiy, Alena Zakharenko and Pavel Petrov

J. Mar. Sci. Eng. 2023, 11(4), 797; https://doi.org/10.3390/jmse11040797 - 07 Apr 2023

Cited by 3 | Viewed by 815

Abstract

In this study formal derivation of mode coupling equations in underwater acoustics is revisited. This derivation is based on the method of multiple scales from which modal expansion of the field emerges, and the vectorized WKBJ equation for the coefficients in this expansion [...] Read more.

In this study formal derivation of mode coupling equations in underwater acoustics is revisited. This derivation is based on the method of multiple scales from which modal expansion of the field emerges, and the vectorized WKBJ equation for the coefficients in this expansion are obtained in an automatic way. Asymptotic analysis accomplished in this work also establishes a connection between coupled mode parabolic equations in three-dimensional case and the generalized WKBJ solution that emerges as its two-dimensional counterpart. Despite the fact that similar mode coupling equations can be found in literature, in our study a new systematic and formalized approach to their derivation is proposed. A theorem that guarantees asymptotic conservation of the energy flux in the considered two-dimensional waveguide is also proven. Full article

(This article belongs to the Special Issue Sound Scattering in the Ocean)

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22 pages, 10620 KiB

Open AccessArticle

Use of Interference Patterns to Control Sound Field Focusing in Shallow Water

by Sergey Pereselkov, Venedikt Kuz’kin, Matthias Ehrhardt, Sergey Tkachenko, Pavel Rybyanets and Nikolay Ladykin

J. Mar. Sci. Eng. 2023, 11(3), 559; https://doi.org/10.3390/jmse11030559 - 06 Mar 2023

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Abstract

The possibility of controlling localized fields in multimode shallow water waveguides based on the principle of interference invariance was studied. Within the framework of the numerical experiments in a wide frequency range of 100–350 Hz and range intervals of 10–100 km, the possibilities [...] Read more.

The possibility of controlling localized fields in multimode shallow water waveguides based on the principle of interference invariance was studied. Within the framework of the numerical experiments in a wide frequency range of 100–350 Hz and range intervals of 10–100 km, the possibilities of focusing the sound field by wavefront reversal and controlling of the focusing of the focal spot by frequency tuning in shallow water waveguides was analyzed. The focal spot scanning was carried out by frequency tuning with a fixed distribution of the sound field at receiving and transmitting vertical antenna apertures. A comparative analysis of the features of focusing and focal spot control for summer and winter stratification of the water layer was carried out. It is shown that the parameters of the focal spot during frequency tuning were more stable in the winter waveguide. It is demonstrated that the sound frequency tuning had a piecewise continuous character and was carried out on a domain of one continuous track and jump-passing on the other track in accordance with the waveguide interference fringes in the range–frequency domain. Full article

(This article belongs to the Special Issue Sound Scattering in the Ocean)

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15 pages, 727 KiB

Open AccessArticle

Mesh Optimization for the Acoustic Parabolic Equation

by Mikhail Lytaev

J. Mar. Sci. Eng. 2023, 11(3), 496; https://doi.org/10.3390/jmse11030496 - 25 Feb 2023

Cited by 1 | Viewed by 1139

Abstract

This work is devoted to increasing the computational efficiency of numerical methods for the one-way Helmholtz Equation (higher-order parabolic equation) in a heterogeneous underwater environment. The finite-difference rational Padé approximation of the propagation operator is considered, whose artificial computational parameters are the grid [...] Read more.

This work is devoted to increasing the computational efficiency of numerical methods for the one-way Helmholtz Equation (higher-order parabolic equation) in a heterogeneous underwater environment. The finite-difference rational Padé approximation of the propagation operator is considered, whose artificial computational parameters are the grid cell sizes and reference sound speed. The relationship between the parameters of the propagation medium and the artificial computational parameters is established. An optimized method for automatic determination of the artificial computational parameters is proposed. The optimization method makes it possible to account for any propagation angle and arbitrary variations in refractive index. The numerical simulation results confirm the adequacy and efficiency of the proposed approach. Automating the selection process of the computational parameters makes it possible to eliminate human errors and avoid excessive consumption of computational resources. Full article

(This article belongs to the Special Issue Sound Scattering in the Ocean)

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16 pages, 1638 KiB

Open AccessArticle

Low-Frequency Sound Propagation in an Underwater Waveguide with a Giant Gassy Pockmark

by Alexander A. Komissarov, Denis V. Makarov, Andrey O. Kholmogorov and Renat B. Shakirov

J. Mar. Sci. Eng. 2023, 11(1), 211; https://doi.org/10.3390/jmse11010211 - 13 Jan 2023

Cited by 5 | Viewed by 1377

Abstract

Bottom formations known as pockmarks basically arise due to extensive gas emission. Active pockmarks are characterized by exceptionally high gas saturation and substantially reduced sound speed. The latter circumstance leads to strong attenuation of sound waves contacting with a pockmark. In the present [...] Read more.

Bottom formations known as pockmarks basically arise due to extensive gas emission. Active pockmarks are characterized by exceptionally high gas saturation and substantially reduced sound speed. The latter circumstance leads to strong attenuation of sound waves contacting with a pockmark. In the present paper, we study low-frequency sound propagation in a 10-km long waveguide crossing a giant pockmark. A new method of acoustic waveguide scanning based on measurement of the wavefield propagator is represented. This method allows one to explore attenuation anomalies associated with the presence of the gas-saturated bottom region. In particular, one can find out which beams fall into a pockmark area and therefore experience strong losses. Identifying such beams, as well as beams which avoid pockmark-assisted losses, one can estimate probable locations of the pockmark segment in the waveguide, provided information about the background medium is sufficient. Full article

(This article belongs to the Special Issue Sound Scattering in the Ocean)

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10 pages, 2358 KiB

Open AccessArticle

Angular Spectrum of Acoustic Pulses at Long Ranges

by Denis V. Makarov and Leonid E. Kon’kov

J. Mar. Sci. Eng. 2023, 11(1), 29; https://doi.org/10.3390/jmse11010029 - 27 Dec 2022

Viewed by 1209

Abstract

Long-range propagation of sound pulses in the deep ocean is considered. A new method for the estimation of the pulse angular spectrum is presented. The method is based on the Husimi transform of a wave field and can be realized with a short [...] Read more.

Long-range propagation of sound pulses in the deep ocean is considered. A new method for the estimation of the pulse angular spectrum is presented. The method is based on the Husimi transform of a wave field and can be realized with a short vertical array of nondirectional hydrophones. As a result, one obtains a diagram of the arrival pattern in the time–angle plane. The method is applied to a model of the underwater sound channel in the Sea of Japan. Special attention is paid to sound scattering on a cold synoptic eddy along the waveguide. It is shown that the synoptic eddy leads to a splitting of the individual ray’s arrivals into clusters with close angles and times. The random sound-speed perturbation induced by internal waves blurs these clusters into a fuzzy background and simultaneously broaden the angular spectrum of pulses. Nevertheless, it is found that the latter effect is relatively weak for short vertical arrays. In particular, it is shown that increasing the array length from 10 to 30 m results in the separation of the arrivals with opposite angles. Full article

(This article belongs to the Special Issue Sound Scattering in the Ocean)

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11 pages, 9414 KiB

Open AccessArticle

Some Peculiarities of Low-Frequency Hydroacoustic Signals Behavior in Tomographic Studies of “Sea-Land-Sea” System

by Sergey Budrin, Grigory Dolgikh, Vladimir Chupin and Stanislav Dolgikh

J. Mar. Sci. Eng. 2022, 10(10), 1550; https://doi.org/10.3390/jmse10101550 - 20 Oct 2022

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Abstract

In this paper, we analyzed the results of experimental data processing in the study of regularities of propagation and transformation of low-frequency harmonic signals at the boundary of the “sea−land−sea” system. Harmonic signals at a carrier frequency of 33 Hz were generated by [...] Read more.

In this paper, we analyzed the results of experimental data processing in the study of regularities of propagation and transformation of low-frequency harmonic signals at the boundary of the “sea−land−sea” system. Harmonic signals at a carrier frequency of 33 Hz were generated by a low-frequency hydroacoustic radiator in Vityaz Bay. Then, they passed along the shelf of decreasing depth, transformed into seismoacoustic signals of the upper layer of the Earth’s crust and the bedrocks of Shultz Cape and excited hydroacoustic signals at the corresponding frequency in the shelf waters in the open part of the Sea of Japan. When processing the experiment results, we obtained the vertical distributions of the pressure field, caused by an acoustic low-frequency signal passing through the upper layer of the Earth’s crust. We presented the distributions of hydroacoustic and seismoacoustic energies. The obtained experimental data were compared with the simulations by the model, developed strictly according to the experiment scheme and the geological structure of the area. In the discussion of the obtained results, we explained a probable mechanism of acoustic energy propagation and the nature of the vertical distributions of the pressure field formation. Full article

(This article belongs to the Special Issue Sound Scattering in the Ocean)

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17 pages, 494 KiB

Open AccessArticle

Coupled-Mode Parabolic Equations for the Modeling of Sound Propagation in a Shallow-Water Waveguide with Weak Elastic Bottom

by Sergey Kozitskiy

J. Mar. Sci. Eng. 2022, 10(10), 1355; https://doi.org/10.3390/jmse10101355 - 22 Sep 2022

Cited by 5 | Viewed by 1575

Abstract

In this work, a mode parabolic equation method with interacting modes accounting for the weak elasticity at the bottom is developed. An important feature of the proposed method is that computations of elastic modes are avoided and that the solution is obtained in [...] Read more.

In this work, a mode parabolic equation method with interacting modes accounting for the weak elasticity at the bottom is developed. An important feature of the proposed method is that computations of elastic modes are avoided and that the solution is obtained in the form of expansion over acoustic modes. A numerical technique for solving resulting mode parabolic equations is developed, and the accuracy and efficiency of the resulting solution is validated by a direct comparison against source image solutions in the 3D wedge benchmark problem. Satisfactory agreement of the two solutions is achieved for sufficiently small values of shear wave speed that are typical for soft sediments of the sea bottom. The developed approach may be used for solving 3D problems of sound propagation with the elastic properties of bottom sediments taken into account. Full article

(This article belongs to the Special Issue Sound Scattering in the Ocean)

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20 pages, 20153 KiB

Open AccessArticle

On Sound Scattering and Acoustic Properties of the Upper Layer of the Sea with Bubble Clouds

by Vladimir A. Bulanov, Lubov K. Bugaeva and Andrey V. Storozhenko

J. Mar. Sci. Eng. 2022, 10(7), 872; https://doi.org/10.3390/jmse10070872 - 25 Jun 2022

Cited by 3 | Viewed by 1467

Abstract

The presence of bubbles near the sea surface under certain conditions leads to abnormal sound scattering and a significant change in the acoustic properties of the upper layer of the sea. The article presents some results of sound scattering studies under various sea [...] Read more.

The presence of bubbles near the sea surface under certain conditions leads to abnormal sound scattering and a significant change in the acoustic properties of the upper layer of the sea. The article presents some results of sound scattering studies under various sea conditions, up to stormy conditions, when extensive bubble clouds arise. By the method of unsteady acoustic spectroscopy, data on the size distribution of bubbles at various depths have been obtained, which can be described by a power function with exponential decay at small bubble sizes of the order of 10 microns. Estimates of the gas content in bubble clouds and their influence on the acoustic characteristics of the upper layer of the sea have been carried out. It is shown that at sufficiently high concentrations, sharp increases in absorption and dispersion of the sound velocity are observed. Modeling of sound propagation in the presence of a quasi-homogeneous bubble layer shows that it leads both to a change in the laws of the average decay of the sound field along the sound propagation path and to a change in the shallow spatial structure of the field. Full article

(This article belongs to the Special Issue Sound Scattering in the Ocean)

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17 pages, 4651 KiB

Open AccessArticle

On Average Losses of Low-Frequency Sound in a Two-Dimensional Shallow-Water Random Waveguide

by Oleg E. Gulin and Igor O. Yaroshchuk

J. Mar. Sci. Eng. 2022, 10(6), 822; https://doi.org/10.3390/jmse10060822 - 15 Jun 2022

Cited by 4 | Viewed by 1497

Abstract

For a low-frequency sound signal propagating in a two-dimensionally inhomogeneous shallow-water waveguide, the influence of random bathymetry (fluctuating bottom boundary) was considered based on the local-mode approach and statistical modeling using first-order evolution equations. The study was carried out in shallow sea conditions [...] Read more.

For a low-frequency sound signal propagating in a two-dimensionally inhomogeneous shallow-water waveguide, the influence of random bathymetry (fluctuating bottom boundary) was considered based on the local-mode approach and statistical modeling using first-order evolution equations. The study was carried out in shallow sea conditions corresponding to the coastal waveguides of the Russian Arctic seas. Here, a feature was the presence of an almost homogeneous water layer with various characteristics of seabed sediments. To describe the latter, a random model of the impedance was adopted. For the conditions of a strongly penetrable bottom boundary, on average, the calculations predicted adequate weak effects of bathymetry fluctuations on the average sound intensity compared to the effect of fluctuations in the sediment parameters and volumetric random inhomogeneities of the water column. In addition, it was shown that, in terms of statistics, the roughness of the bottom boundary perturbed the average sound intensity in a shallow-water waveguide differently than volumetric fluctuations in the speed of sound. The dependence of the statistical effects (the first and second moments of the signal intensity) on the parameters of the waveguide and the frequency range was studied. As a result of numerical modeling, comparative quantitative estimates of the influence of both the random roughness of the bottom interface and fluctuations of bottom sediment parameters on the average losses of the propagating signal, not presented in the literature, were obtained. Full article

(This article belongs to the Special Issue Sound Scattering in the Ocean)

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18 pages, 1850 KiB

Open AccessArticle

Surface Waves Prediction Based on Long-Range Acoustic Backscattering in a Mid-Frequency Range

by Alexey V. Ermoshkin, Dmitry A. Kosteev, Alexander A. Ponomarenko, Dmitrii D. Razumov and Mikhail B. Salin

J. Mar. Sci. Eng. 2022, 10(6), 722; https://doi.org/10.3390/jmse10060722 - 25 May 2022

Cited by 5 | Viewed by 1715

Abstract

Underwater acoustic echosounding for surface roughness parameters retrieval is studied in a frequency band that is relatively new for such purposes. During the described 2-weeks sea experiment, 1–3 kHz tonal pulses were emitted from an oceanographic platform, located on the northern Black Sea [...] Read more.

Underwater acoustic echosounding for surface roughness parameters retrieval is studied in a frequency band that is relatively new for such purposes. During the described 2-weeks sea experiment, 1–3 kHz tonal pulses were emitted from an oceanographic platform, located on the northern Black Sea shelf. Doppler spectra of the resulting reverberation were studied. The frequency band of the acoustic system, selected for this study, is chosen due to the fact that the sound propagation range is large enough for remote sensing in a coastal zone, and the resolution cell size does not limit the research. Backscattering of acoustical signals was received for distances around two nautical miles. However, it turned to be quite difficult to interpret the obtained data since backscattering spectrum shape was influenced by a series of effects, resulting in a complicated link to wind waves and currents’ parameters. Significant wave height and dominant wave frequency were estimated as the result of such signals processed with the use of machine learning tools. A decision-tree-based mathematical regression model was trained to solve the inverse problem. Wind waves prediction is in a good agreement with direct measurements, made on the platform, and machine learning results allow physical interpretation. Full article

(This article belongs to the Special Issue Sound Scattering in the Ocean)

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