Sound Propagation Research Articles

Modeling and simulation analysis of hydroacoustic field under ice

In order to study the effect of polar ice on sound propagation in seawater, the finite element method was used to establish a seawater sound propagation model with and without ice, and the influence of the presence of ice on the seawater sound propagation law was analyzed. The simulation results show that the energy of sound propagation in seawater has a certain loss when there is an ice layer compared with the case of no ice layer. Through frequency domain analysis, the propagation process of sound energy in seawater can be clearly seen. Normally, the sound energy generated by a point source at a suitable location will return to the seawater after passing through the sea surface, while after the addition of the ice layer, part of the sound energy generated by the point source will be lost to the air through the ice layer, resulting in a reduction of the acoustic energy returned to the seawater. As a result, there is less acoustic energy in the seawater than in the ice-free case.

Sound propagation modeling in forests using the transmission line matrix method: Comparison with experimental in situ measurements

We present efforts to adapt the time-domain Transmission Line Matrix (TLM) method for modeling sound propagation in forests. It is relevant to professionals and researchers in environmental acoustics and to those interested in studying sound propagation in outdoor environments using numerical modeling techniques. The study aims to demonstrate the applicability of the method in complex media where sound waves undergo multiple reflections combined with ground effects during their propagation from a sound source to a receiver point. The TLM method is used to numerically model sound propagation in a 3D forest geometry generated based on a real tree distribution case. Data from an experimental campaign conducted in the rainforest of French Guyana are used as a reference. The results show an encouraging comparison between them and the in situ measurements, even if the hypotheses made to adapt the input data in the model were strong. We find that more measurement points and more specifications (ground impedance measurements, canopy density, etc.) about the experimental site are needed for further simulations, even if obtaining them presents technical difficulties.

Teaching concepts of acoustics in air—Part 3, reverberation

This paper has been written to participate in the “Education in Acoustics” session at the 2024 joint conference of the Canadian Acoustical Association and the Acoustical Society of America. It is written to build on Parts 1 and 2 of this series and similarly contains materials extracted from 30 years of teaching to Architects at the University of Waterloo and Dalhousie University in Halifax. Part 1 dealt primarily with sound propagation in air and the concepts of longitudinal wave motion, speed, frequency and wavelength and related effects which relate to what we perceive as pitch. Part 2 expanded on those concepts by discussing superposition and the definition and measurement of sound pressure, decibels and the decibel scale and how to manage decibels, all of which we perceive as loudness. Part 3 deals with reverberation, which is arguably the most important aspect of how sound propagates in indoor spaces. It affects both our ability to communicate and how we experience and perceive the quality of the acoustical environment. Practical demonstrations are provided to enhance learning of the concept of Reverberation. These include “hands on” demonstrations including physical experimentation, an audio demonstration and written materials to advance the concept.

How will climate change affect the underwater sound environment? Modelling the potential effects of climate change on the oceanic speed of sound

The purpose of this study is to create a year-by-year prediction model for surface-level oceanic speed of sound in different future climate scenarios and discuss how these results may be relevant for current and future work in underwater acoustics. It is already understood that sound propagation and speed in the oceans will be affected by future changes of oceanic pressure, temperature, salinity, and acidity. Certain trends of future sound speed have been analyzed in precedent studies; however, there are some information gaps and the availability of future oceanic sound speed models for use by the acoustical industry is lacking. This study intends to fill in some of these gaps and initiate an interdisciplinary discussion between both research and industry professionals in the field of acoustics.

Acoustic propagation through a biological deep scattering layer at the New England shelf break

The New England Shelf Break is a dynamic ocean environment with strong spatial variability due to complex physical processes and interactions with warm core rings originating from the Gulf Stream. An acoustic autonomous underwater vehicle (AUV) was deployed in the New England Shelf Break Acoustics (NESBA) experiment in May 2021 to investigate environmental variability and its effect on sound propagation. The AUV system was comprised of a modified REMUS 600 vehicle with a hull-mounted 3.5 kHz transducer, a downward-facing EK80 echosounder, and a towed linear hydrophone array. Shipboard EK80 data measured during the AUV mission showed the presence of a biological deep scattering layer. Preliminary analysis of AUV source signals passing through the layer suggested significant attenuation compared to signals not passing through the layer. To investigate this further, a parabolic equation (PE) model with range-dependent attenuation patches in the water column was constructed to replicate the biological attenuation through the scattering layer. The model uses estimates of absorption and scattering derived from shipboard and AUV EK80 data. Through this study we aim to better understand the scattering effects of this deep biological layer on acoustic propagation. [Work supported by the Office of Naval Research.]

Verifying turbulence models in the atmospheric boundary layer by acoustical means

The impacts of turbulence on sound propagation in the atmospheric boundary layer (ABL) are important in many practical applications such as acoustic source localization, sonic boom propagation, and auralization of flying aircraft. However, turbulence impacts can vary dramatically in response to changing meteorological conditions. To address this issue, a turbulence spectral model has been introduced that captures the complexities of turbulence generation by wind shear, buoyancy instabilities, and ground blocking in the ABL. An experiment on vertical and slanted sound propagation through the ABL was conducted to verify the model. Various statistical characteristics of sound signals, including variances of the log-amplitude and phase fluctuations, coherences, and signal probability distributions were measured and compared to theoretical predictions. The dependence of the statistics on meteorological conditions was found to be accurately predicted in conditions of well-developed turbulence, as occurs in windy conditions and the daytime. Predictions in conditions of weak and intermittent turbulence, as often occur at night and around sunrise and sunset, remain challenging.

Subsurface acoustic ducts in the Northern California current system.

This study investigates the subsurface sound channel or acoustic duct that appears seasonally along the U.S. Pacific Northwest coast below the surface mixed layer. The duct has a significant impact on sound propagation at mid-frequencies by trapping sound energy and reducing transmission loss within the channel. A survey of the sound-speed profiles obtained from archived mooring and glider observations reveals that the duct is more prevalent in summer to fall than in winter to spring and offshore of the shelf break than over the shelf. The occurrence of the subsurface duct is typically associated with the presence of a strong halocline and a reduced thermocline or temperature inversion. Furthermore, the duct observed over the shelf slope corresponds to a vertically sheared along-slope velocity profile, characterized by equatorward near-surface flow overlaying poleward subsurface flow. Two potential duct formation mechanisms are examined in this study, which are seasonal surface heat exchange and baroclinic advection of distinct water masses. The former mechanism regulates the formation of a downward-refracting sound-speed gradient that caps the duct near the sea surface, while the latter contributes to the formation of an upward-refracting sound-speed gradient that defines the duct's lower boundary.

Solutions to muddy (geoacoustic inversion) problems

Waveguide propagation is a ubiquitous topic in ocean acoustics. This presentation focuses on low-frequency (f < 500 Hz) sound propagation in coastal oceans (water depth shallower than 500 m). These environments are highly dynamical and complex, and act as dispersive waveguides, bounded by the sea-surface and the seafloor. The underwater acoustic field can thus be described by a set of modes that propagate with frequency-dependent speeds. Propagation of transient acoustic signals to a distant receiver (range > 1 km) accrues multi-modal dispersion information about the propagation medium. To extract relevant information about the oceanic environment from the acoustic recording, physics-based processing methods must be used. In this presentation, I will briefly review modal propagation and time-frequency analysis. I will then show how these approaches can be combined into a non-linear signal processing method dedicated to extracting modal information from a single receiver: this information is the foundation of a transdimensional inversion method used to characterize the oceanic environment. This method will be used to perform geoacoustic inversion on the New England Mud Patch. Using several datasets collected under different oceanographic conditions, I will notably demonstrate a successful estimation of the seafloor properties, consistent with geophysical core measurements and other inversion studies, even when the water column is dynamical and mostly unknown.

Reconstruction of Thermocline Depth based on Machine Learning

The thermocline, as a special structure in the ocean temperature field, has an important impact on sound propagation, material transport, and human underwater activities in the ocean. Using existing methods, the thermocline is distributed underwater and cannot be observed in real-time and with high spatiotemporal accuracy. It can only be calculated from measured data. In previous studies, it was demonstrated that the ocean thermocline is significantly correlated with its sea surface elements. Based on machine learning methods, this paper uses sea level anomaly, sea surface temperature, sea surface salinity, time, longitude and latitude, as well as the vertical gradient method to calculate the depth of the thermocline as data. By constructing a Random Forest model, the regression relationship between the thermocline and sea surface elements and spatiotemporal elements is obtained, this thermocline reconstruction model has a good fitting effect on thermocline depth, with a fitting coefficient of 0.85, and its accuracy has been evaluated. This paper also evaluated the feature importance of the six input data of the model. The results showed that the three sea surface parameters had similar importance, with sea surface temperature having the most significant impact on the depth of the thermocline. The final model can achieve rapid reconstruction of thermocline depth using sea surface information.

Effect of oceanographic fluctuations on geo-acoustic inversions and source localization using ships of opportunity

Several merchant ship-radiated noise events were recorded in two separate seabed characterization experiments in the New England Mudpatch region in 2017 (SBCEX17) and 2022 (SBCEX22). These shallow water acoustic experiments were conducted under different oceanographic conditions, resulting in fluctuations in sound propagation. Several statistical inference approaches are used to invert geo-acoustic parameters such as sound speed and density in a mud over sand sediment (See https://doi.org/10.1121/10.0008419). In this work, we explore the effect of sound speed profile fluctuations in the water column on geo-acoustic inversions in the 360–1100 Hz frequency band. Inversions based on measured and simulated data using acoustic models are provided to support our findings. The results demonstrate that sediment parameters become more sensitive to oceanographic variations as the frequency increases and, therefore, sound speed profile fluctuations in the water column need to be taken into close consideration for more accurate geo-acoustic inversions. [Work supported by ONR].

Tony Embleton—Distinguished researcher, successful manager, consummate acoustician

Tony F. W. Embleton was a distinguished researcher in acoustics. His early career focused on practical noise control projects and experimental non-linear acoustics. Later, Tony made important contributions to the understanding of sound propagation outdoors. Tony spent much of his career at the National Research Council of Canada (NRCC). His professional homes were the ASA and the CAA. Tony received numerous awards from the ASA for his work, including the R. Bruce Lindsay Award in 1964, the ASA Silver Medal in Noise in 1986, and the ASA Gold Medal in 2002 “For fundamental contributions to understanding outdoor sound propagation and noise control and for leadership in the Society.” Tony recognized the value of professional organizations and served the ASA as Vice-President (1977–78) and President (1980–81). He also understood the importance of practical applications in acoustics serving as ASA Standards Director (1993–97), navigating the organization through a tough period, and growing the program toward a solid future. Most importantly, Tony was known for his kind and generous spirit, and his outreach and inspiration to newer colleagues. Many of us are the grateful beneficiaries of his gentle enthusiasm.

Sandiaoling eco-friendly tunnel soundscape and virtual reality analysis

Soundscape of Sandiaoling Ecological Tunnel, a 1.852 km bike path tunnel, has been studied for the taxonomy of sound sources, equivalent sound pressure levels, and the perceived sonic quality. This paper focuses on examining simulated sound source propagations in the tunnel using both omni and directional sound sources with Odeon Room Acoustic software. Additionally, it compares the specific receivers’ auralizations with in situ recorded sounds in a virtual reality model along with a questionnaire to evaluate the distinctions between the two. The preliminary results showed that the simulated sonic quality in tunnel is less reverberant than expected. Proximity of receivers to sound source, the boundary of air to source and receivers inside tunnel as well as the absorption, scattering and transparency coefficients of materials used in simulated model are adjusted. Future work will explore into audio post-production and visual effects.

Moving cargo, keeping whales: Investigating solutions for ocean noise pollution

Human activities introduce high levels of noise into the ocean. Commercial shipping, in particular, has increased to the point that ships make a larger contribution to ocean noise than natural noise sources for most ocean locations and over a broad range of frequencies. Primeval ocean noise levels, those that would have been experienced before the advent of human-made noise in the ocean, are largely unknown. Ocean noise monitoring efforts began post-industrialization, leaving baseline sound levels under which marine organisms evolved unclear. This study modeled primeval (wind-driven) ocean noise levels and modern (ship noise plus wind noise) ocean noise levels in the Santa Barbara Channel off Southern California. The modern noise levels were validated with acoustic measurements from two sites equipped with High-frequency Acoustic Recording Packages. There was good agreement between the modern noise level models when compared to measured levels for high frequencies, and at a site shielded by islands from long range sound propagation. The lower frequency acoustic environment, modeled at 50 Hz, was more degraded than the higher frequency noise levels, modeled at 1000 Hz. This model can be used to identify target regions and times for noise reduction efforts, as well as model future scenarios for noise reduction to identify techniques with the greatest potential for conservation.

Development of a biofidelic acoustic test fixture and evaluation in impulsive noise

Here, we describe the development and use of a novel biofiedlic head surrogate for evaluating head and hearing protection devices against impulsive, shock, and blast insults. The head surrogate, derived from biomedical imagery, includes biofidelic pinnea, ear canals, and skull. In addition to microphones positioned at the ear canal terminus, the surrogate includes accelerometers and a hydrophone to provide an estimate of sound propagation through the bone-conduction pathways. This allows use of the surrogate to estimate a device's ability to attenuate bone-conducted pressure waves. We discuss the tradeoffs between biofidelity, manufacturability, instrumentation, and cost. We will show example data from various test campaigns, including the estimating the attenuation of the bone-conduction pathway afforded by different helmet systems during a 178 dB SPL (peak) shock insult. We will conclude with a look towards the future, including potentially updating the underlying three dimensional models to align with modern biomedical models and databases.

Graduate acoustics at Brigham Young University

Graduate studies in acoustics at BYU prepare students for industry, research, and academia by complementing in-depth coursework with publishable research. Coursework provides students with a foundation in acoustical principles, practices and measurement skills, including a experimental techniques and technical writing. Labs across the curriculum cover calibration, directivity, scattering, absorption, laser Doppler vibrometry, experimental methods for dynamic structures, lumped-element mechanical systems, equivalent circuit modeling, arrays, filters, room acoustics, active noise control, and near-field acoustical holography. Recent thesis and dissertation topics include active noise control, directivity, room acoustics, energy-based acoustics, time reversal, nondestructive evaluation, vibration and acoustics of aerospace vehicles, biomedical applications, flow-based acoustics, voice production, aeroacoustics, sound propagation modeling, nonlinear propagation, high-amplitude noise analyses, machine and deep learning applied to ambient noise level prediction, crowd noise interpretation, and underwater acoustic source localization, and ocean environment classification. Graduate students are expected to present research at professional meetings and publish in peer-reviewed acoustics journals. Graduate students often serve as peer mentors to undergraduate students on related projects and may participate in field experiments to gain additional experience. @BYUAcoustics

The Graduate Program in Acoustics at Penn State

The Graduate Program in Acoustics at Penn State offers graduate degrees (M.Eng., M.S., Ph.D.) in Acoustics, with courses and research opportunities in a wide variety of subfields. Our 820 alumni are employed around the world in military and government labs, academic institutions, consulting firms, and consumer audio and related industries. Our 40 + faculty from several disciplines conduct research and teach courses in structural acoustics, nonlinear acoustics, architectural acoustics, signal processing, aeroacoustics, biomedical ultrasound, transducers, computational acoustics, noise and vibration control, acoustic metamaterials, psychoacoustics, and underwater acoustics. Course offerings include fundamentals of acoustics and vibration, electroacoustic transducers, signal processing, acoustics in fluid media, sound and structure interaction, digital signal processing, experimental techniques, acoustic measurements and data analysis, ocean acoustics, architectural acoustics, noise control engineering, nonlinear acoustics, outdoor sound propagation, computational acoustics, biomedical ultrasound, flow induced noise, spatial sound and three-dimensional audio, and the acoustics of musical instruments. Distance education students pursuing the M.Eng. degree join resident students in a hybrid classroom environment. This poster highlights faculty research areas, laboratory facilities, student demographics, successful graduates, and recent enrollment and employment trends.

Effects of seabed corrugation and stratification on 3D acoustic propagation along the New England Shelf Break

Acoustic signals transmitted and recorded during the New England Shelf Break Acoustics Experiment in 2021 (NESBA) display evidence of complex scattering effects which were not captured in in situ modeling efforts. In particular, although the acoustic parabolic equation models used can predict later arrivals of a single transmission, initial arrivals show mismatch between model predictions and observation. In this presentation, estimates of sub-bottom sediment structure are supplemented by a high-resolution model of the bathymetry to simulate 3D sound propagation across a realistic seabed. The influence of the seabed corrugation and stratification on acoustic arrival times is examined in the context of the NESBA environment. [This research is supported by the Office of Naval Research].

Highlights from the technical committee on noise

The Technical Committee on Noise (TCNS) includes researchers and industry practitioners interested in understanding noise generation from a variety of sources, its propagation, and its impact on structures, objects, and people. The goal of reducing the impact of this noise, or unwanted sound, has led to innovative model development, measurement techniques, mitigation strategies, and input towards the establishment of regulations. Community noise definition and abatement is of particular interest and motivates the advancement of research on a variety of topics, such as transportation noise from traditional and new vehicles, hearing protection, jet and rocket noise, building systems noise and vibration, atmospheric sound propagation, soundscapes, and low-frequency sound. The diverse technical background of TCNS members is essential, given the interdisciplinary nature of this research, and it is mirrored in the topics of special sessions typically held jointly with other ASA technical committees.

Evaluation of data-driven neural operators in ocean acoustic propagation modeling

Various types of neural networks have been employed to tackle a wide range of complex partial differential equations (PDEs) and ordinary differential equations (ODEs). Notably, neural operators such as DeepONet and FNO show promise in handling these problems, offering potential real-time prediction capabilities. In contrast to physics-informed neural network (PINN) methods, neural operators primarily derive insight from extensive, well-prepared datasets. In the context of ocean acoustic propagation modeling, where the challenge involves solving the wave or Helmholtz equation given specific boundary conditions, this study focuses on assessing the performance of data-driven neural operators in predicting sound pressure. Unlike conventional approaches that map between finite-dimensional Euclidean spaces, neural operators excel in learning mappings between infinite-dimensional function spaces—a particularly advantageous feature in sound propagation modeling tasks. This research specifically delves into evaluating the generalization capabilities of neural operators when applied to sound propagation modeling in a range-independent shallow water environment. By exploring the neural operators' effectiveness in this domain, the study aims to contribute valuable insights into their potential applications for real-world ocean acoustics simulations.

Energy density source levels of underwater explosive charges

This paper presents experimental measurements of energy density source levels of small explosive charges for high frequencies to 18 kHz. The experiments were carried out using Signals Underwater Sound (SUS) charges deployed at a deep water site in a coastal fiord north of Vancouver BC. The waveform of an underwater explosion is characterized by a high intensity shock wave signal followed by a series of bubble pulses of decreasing intensity. The bubble pulses dominate the SUS energy density spectrum at frequencies below 1 kHz, but at higher frequencies the spectrum is dominated by the characteristics of the decay envelope of the shock wave signal. The explosive material in SUS charges is packed in a thin cylindrical cavity, resulting in a non-uniform decay envelope with secondary pulses when detonated, and a non-spherical distribution of the radiated sound. The impact of the cylindrical charge shape on energy density source level was investigated experimentally. Data were recorded for SUS deployments that generated in-line and broadside sound propagation to the receiver with respect to the axis of the cylindrical charge. Experimental measurements indicate significant differences in the high frequency SUS energy density spectrum depending upon the SUS and receiver geometry.