Sound Propagation In Ocean Research Articles

Predicting ocean pressure field with a physics-informed neural network.

Ocean sound pressure field prediction, based on partially measured pressure magnitudes at different range-depths, is presented. Our proposed machine learning strategy employs a trained neural network with range-depth as input and outputs complex acoustic pressure at the location. We utilize a physics-informed neural network (PINN), fitting sampled data while considering the additional information provided by the partial differential equation (PDE) governing the ocean sound pressure field. In vast ocean environments with kilometer-scale ranges, pressure fields exhibit rapidly fluctuating phases, even at frequencies below 100 Hz, posing a challenge for neural networks to converge to accurate solutions. To address this, we utilize the envelope function from the parabolic-equation technique, fundamental in ocean sound propagation modeling. The envelope function shows slower variations across ranges, enabling PINNs to predict sound pressure in an ocean waveguide more effectively. Additional PDE information allows PINNs to capture PDE solutions even with a limited amount of training data, distinguishing them from purely data-driven machine learning approaches that require extensive datasets. Our approach is validated through simulations and using data from the SWellEx-96 experiment.

Using Bayesian optimization to refine laboratory tank sound propagation modeling

Because ocean measurements are costly, a laboratory water tank provides opportunities to take scaled measurements and develop approaches to machine learning that are transferable to ocean acoustic problems. These applications are better achieved if reflections off the side walls are significantly reduced. To reduce these reflections, the side walls of the tank are lined with Aptile SF5048 echo reducing tiles made by Precision Acoustics. This work studies the extent to which two ocean sound propagation models (namely ORCA and BELLHOP) can predict relative transmission loss as a function of source-receiver range and frequency. The modeling parameters of sound speed and density that determine the reflections at the bottom of the tank were refined through a Bayesian optimization algorithm. We found that the optimized parameters improve the model-data agreement and that the models fit the data at certain frequencies corresponding mainly to peaks in the echo reduction for the Aptile panels. This agreement implies that at certain frequencies, sound propagation in our tank acts as it would in a large body of water. Using our tank as a testbed for developing machine learning algorithms is a reasonable approach.

OPTIMUM PROPAGATION IN OCEAN: THE COMPARISON BETWEEN NORMAL MODE AND EMPIRICAL FRANCOIS-GARRISON FORMULA

There are not only theory but also the empirical formula to deal with the problem of sound propagation in ocean. As such the Normal mode and Francois-Garrison are typical methods. Optimum sound propagation in ocean is the way we unify these two methods. In this paper, we investigate the transmission losses of both Normal mode and Francois- Garrison at some frequencies (170Hz, 800Hz, 100 KHz) at shallow water conditions (Tonkin gulf). The calculated and simulation results show that the optimum is achieved when the Normal mode is used at low frequencies whereas the Francois-Garrison is used at high frequencies.

Ocean Sound Propagation in a Changing Climate: Global Sound Speed Changes and Identification of Acoustic Hotspots

AbstractClimate change is a relevant threat on a global scale, leading to impacts on ecosystems and ocean biodiversity. A considerable fraction of marine life depends on sound. Marine mammals, in particular, exploit sound in all aspects of their life, including feeding and mating. This work explores the impact of climate change in sound propagation by computing the three‐dimensional global field of underwater sound speed. The computation was performed based on present conditions (2006–2016) and a “business‐as‐usual” future climate scenario (Representative Concentration Pathway 8.5), identifying two “acoustic hotspots” where larger sound speed variations are expected. Our results indicate that the identified acoustic hotspots will present substantial climate‐change‐induced sound speed variations toward the end of the century, potentially affecting the vital activities of species in the areas. Evidence is provided of the impact of such variation on underwater sound transmission. As an example of a species impacted by underwater transmission, we considered one marine mammal endangered species, the North Atlantic right whale (Eubalaena glacialis), in the northwestern Atlantic Ocean. To the best of our knowledge, this is the first global‐scale data set of climate‐induced sound speed changes expected under a future scenario. This study provides a starting point for policies oriented research to promote the conservation of marine ecosystems and, in particular, endangered marine mammals.

Frank Press, A life of magnitude

Frank Press, 19th president of the National Academy of Sciences, died on Wednesday, January 29, 2020, at his home in Chapel Hill, North Carolina, at the age of 95. His career spanned the golden age of postwar science, and its arc took him to the highest levels of leadership in academia and government. Frank served in many roles with great distinction and is remembered for his sharp intellect and steady leadership and for his self-composure, fair-mindedness, and good judgment. Few scientists of the past century have had such an enduring impact on United States science policy and the organization of the federal scientific enterprise. Frank Press. Image credit: Ohio History Connection/Joseph Munroe. Frank was born in New York City, the child of Russian emigres, graduating from the Samuel J. Tilden High School in the East Flatbush section of Brooklyn in 1941. He received his bachelor’s degree in physics from the City College of New York in 1944 and enrolled as a graduate student at Columbia University. Frank married Billie Kallick in 1946, when he was 21 years old. She was the love of his life and constant companion until her death in 2009. At Columbia, Frank studied sound propagation in oceans under the supervision of the geophysicist and oceanographer Maurice “Doc” Ewing. He received his doctorate in 1949, the same year that Ewing founded the Lamont Geological Observatory on a cliff overlooking the Hudson River. With generous funding from the Defense Department, Ewing and his two assistant professors, Frank and Joe Worzel, quickly developed Lamont into a world-class research laboratory. Frank learned a lot from Ewing’s hard-driving style and quoted his advice, “Make a better instrument or measure in a place where no one else has been and a great discovery will come your way.” Following this dictum, Frank expanded … [↵][1]1Email: tjordan{at}usc.edu. [1]: #xref-corresp-1-1

Effective representation of sound propagation in ocean using Hartree-Fock Bogoliubov theory

Physical insight into the complexities of sound propagation in the ocean can be achieved by considering effective waveguides; for example, Zhao et al., “Modeling of Green's function with bottom reflective parameters (P,Q) instead of Geoacoustic parameters,” J. C. A. 22(1), 1440005, (2014).). In principle, effective waveguide representations can enhance the efficacy of solving the statistical inverse problem. Inspired by such work, an attempt is made to utilize methods to solve the quantum many-body problem. One way to solve the nuclear many-body problem (NMBP) is to transform a group of strongly interacting particles into a set of weakly interacting particles within a potential that results from the collective nature of the two-body interactions. The most noteworthy of these approaches is the Hartree-Fock-Bogoliubov (HFB) theory. In analogy with the NMBP we replace an ocean acoustics problem that is described by a set of strongly coupled modes with a self-consistent modal potential that contains all the long-range quasi-mode correlations. Computational results are provided that compares the standard coupled mode solution to the HFB generated solution.

Optimal Path Design of Underwater Acoustic Network Based on RAP

Reliable Acoustic Path (RAP) is one of the special physical phenomenon in the deep ocean sound propagation, in a certain extent, it can reflect the deep-ocean sound propagation characteristics. In this paper, the sound propagation characteristics in RAP are analyzed, and the transmission loss is calculated by Bellhop acoustic software, which is used to determine if the network nodes can connect. In this article, with the dynamic grid planning algorithm, the node layout scheme for the optimal path in deep-ocean underwater acoustic network based on the deep-ocean underwater acoustic network node.

Random Matrix Theory for Low-Frequency Sound Propagation in the Ocean: A Spectral Statistics Test

Problem of long-range sound propagation in the randomly-inhomogeneous deep ocean is considered. We examine a novel approach for modeling of wave propagation, developed by Hegewisch and Tomsovic. This approach relies on construction of a wavefield propagator using the random matrix theory (RMT). We study the ability of the RMT-based propagator to reproduce properties of the propagator corresponding to direct numerical solution of the parabolic equation. It is shown that mode coupling described by the RMT-based propagator is basically consistent with the direct Monte-Carlo simulation. The agreement is worsened only for relatively short distances, when long-lasting cross-mode correlations are significant. It is shown that the RMT-based propagator with properly chosen range step can reproduce some coherent features in spectral statistics.

The internal wave prediction component of the Integrated Ocean Dynamics and Acoustics Project

The accuracy of ocean sound propagation modeling depends on properly representing the environment. The water column portion of this has phenomena and features that are time- and space-dependent, covering a huge range of scales. Nonlinear internal gravity waves (nonlinear internal waves, NIW) in shallow areas are important features that are moving, evolving and anisotropic, and whose effects can be handled properly only with 3D sound modeling. Thus, 3D NIW field predictions would be needed for comprehensive modeling. One challenging part of our project to make acoustic condition forecasts from available data involves making this 3D NIW field prediction using data-assimilating regional models that do not faithfully handle NIW. Our methods for extracting internal tide signals from the models, analyzing their propagation into regions where they transform in reality to NIW (but not in the models), and predicting NIW conditions in these regions are explained here. Outstanding challenges such as how to parameterize internal-tide coupled mode propagation on slopes and how to model highly nonlinear crossing NIW groups will be presented. The question of what constitutes an effective NIW prediction for acoustic purposes will be addressed.

Recent studies of three-dimensional sound propagation in Ocean based on wave theory method

Recent studies of three-dimensional sound propagation in Ocean based on wave theory method

The study of sono-elasticity of floating bodies in the acoustical environment of shallow sea

A concept combining sono-elasticity research field with oceanic sound propagation research field in developed in this paper. The paper formulates in details about how to transfer the sono-elasticity dynamic equations together with oceanic sound propagation equations in theoretical model into related numerical program by using the PEKERIS neritic acoustic environment as an example. The further verification of this approach and related computing program, and analyses on characteristics of the structural vibration and acoustic radiation in neritic acoustic environment are also provided in the paper by analyzing the problem of a elastic spherical shell as an example. Keywords:Sono-elasticity; Sound propagation; Shallow sea; Spherical shell.

Statistics of low-frequency normal-mode amplitudes in an ocean with random sound-speed perturbations: Shallow-water environments

Second- and fourth-moment mode-amplitude statistics for low-frequency ocean sound propagation through random sound-speed perturbations in a shallow-water environment are investigated using Monte Carlo simulations and a transport theory for the cross-mode coherence matrix. The acoustic observables of mean and mean square intensity are presented and the importance of adiabatic effects and cross-mode coherence decay are emphasized. Using frequencies of 200 and 400 Hz, transport theory is compared with Monte Carlo simulations in a canonical shallow-water environment representative of the summer Mid-Atlantic Bight. Except for ranges less than a horizontal coherence length of the sound structure, the intensity moments from the two calculations are in good agreement. Corrections for the short range behavior are presented. For these frequencies the computed mode coupling rates are extremely small, and the propagation is strongly adiabatic with a rapid decay of cross-mode coherence. Coupling effects are predicted to be important at kilohertz frequencies. Decay of cross-mode coherence has important implications for acoustic interactions with nonlinear internal waves: For the case in which the acoustic path is not at glancing incidence with a nonlinear internal-wave front, adiabatic phase randomizing effects lead to a significantly reduced influence of the nonlinear waves on both mean and mean square intensity.

Transport equations for cross-frequency transport equations for acoustic intensity moments

The second and fourth moment mode-amplitude statistics for ocean sound propagation through random sound-speed perturbations are investigated using exact transport theory for the cross-frequency cross-mode coherence matrix. These exact equations are derived using the method of successive approximations, originally developed by Klyatskin and Tartarskii. These equations allow the determination of the validity of the usual transport equation (involving the Markov approximation), which is the first order approximation (in a infinite sequence of approximations to the exact equations). The range scales for the approach to the asymptotic behavior of the intensity moments, and the decay of the cross-modal coherence is easily determined at all frequencies.

Frequency domain analysis of acoustic wave propagation in heterogeneous media considering iterative coupling procedures between the method of fundamental solutions and Kansa's method

SUMMARYAcoustic wave propagation in heterogeneous media is a topic of significant interest in many areas of science and engineering, including aeroacoustics and sound propagation in oceans. In the present work, numerical frequency domain models based on the joint use of the method of fundamental solutions and of the radial basis function collocation method (also known as Kansa's method) are discussed. In this context, the method of fundamental solutions is used to model the homogeneous part of the propagation domain, while Kansa's method is employed to model the presence of heterogeneities. The coupling between the two parts of the propagation domain is performed iteratively, allowing independent spatial discretization between the different subdomains of the model (i.e. matching collocation points at common surfaces are not necessary). Additionally, an optimised algorithm, based on the use of a varying relaxation parameter, is employed to speed up and/or to ensure the convergence of the iterative coupling process. At the end of the paper, numerical results illustrate the applicability and potentialities of the proposed formulations. Copyright © 2011 John Wiley & Sons, Ltd.

波動的解析手法の海洋内音波伝搬解析への適用( 音響分野で活用される時間領域有限差分(FDTD)法)

波動的解析手法の海洋内音波伝搬解析への適用( 音響分野で活用される時間領域有限差分(FDTD)法)

Ocean noise level change in response to ocean acidification.

It has been known for several decades that reduction in ocean pH (increase in acidity) would have an impact on ocean sound content and propagation loss. Net flux of carbon dioxide into the ocean has already reduced pH in the upper ocean, and as a result has reduced absorption in those same waters. This trend will likely continue. Based on forecasts of oceanic pH profiles and sound sources, changes in ocean sound content (ambient noise) can be computed. In general, sound energy loss can be partitioned into intrinsic dissipation (the chemical relaxation absorption process) and dissipation in the seafloor, with the boundary loss being analogous to sub-unity reflectivity at the boundaries of a room or concert hall. Here, expected deep ocean noise level changes in various frequency bands from 0.1 to 10 kHz are presented. A model is used that includes basic propagation physics (including the sound channel), depth variability of absorption, loss of sound energy into seafloor, and distributed acoustic sources. At low frequency, little sound is absorbed, so absorption effects are muted. At higher frequencies, sound does not propagate far, also minimizing absorption effects. In the center of the band, there can be sizable effects.

RAY STABILITY FOR BACKGROUND SOUND SPEED PROFILES WITH TRANSITION

In this paper deep ocean sound propagation through random media is considered. The study is conducted within a ray theory framework, which facilitates the assessment of ray stability. Model ocean environments where there is a gradual transition between two ambient sound speed profiles, a single duct Munk profile and a double duct profile taken in the Eastern North Atlantic are examined. We build on the finding that the ambient sound speed structure controls ray stability [Beron-Vera & Brown, 2003], and extend this statement for sound speed profiles with transition. It is shown that launching basins, plots constructed by the Maximal Lyapunov Exponent and indicating desirable ray launching parameters, can be predicted by the unperturbed ray system using the nonlinearity parameter.

Ray methods in long-range deep ocean sound propagation.

Although ray methods have limitations, they remain extremely important because they provide insight into the underlying wave propagation physics that is difficult, if not impossible, to obtain by any other means. In this talk the utility of ray methods in long‐range deep ocean sound propagation will be discussed and illustrated. Topics to be discussed include ray‐mode duality and action quantization; adiabatic invariance for rays and modes; beamforming and Radon transforms; caustics and catastrophes; travel time sensitivity kernels, Fresnel zones and other measures of ray widths; nonlinear resonances, KAM theory, and mode coupling; the waveguide invariant and its ray equivalent; and beam dynamics—from weakly divergent to explosive. [Work supported by ONR.]

A chaos‐based wide‐angle parabolic equation model for sound propagation in random ocean.

Recently, the chaos‐based methods have attracted much attention in ocean acoustics committee. In this paper, a set of partial differential equations (PDEs), which are based on the wide‐angle parabolic equation and Wiener‐chaos decomposition, was established to investigate the propagation of sound propagation in the ocean environment with an arbitrary sound speed profile. Simultaneously, a numerical treatment of the PDEs, which employed an implicit difference scheme and a spectral method, was developed. By using this method, three cases with different kinds of randomness under a distinct ocean environment are studied numerically.

Sound propagation in ocean

Sound propagation in ocean