Measurements Of Sound Propagation Research Articles

Measuring excess attenuation in littoral environments: Evolution of a measurement system

Atmospheric sound propagation measurements over long distances are generally lacking in the literature. This work presents the evolution of the system deployed to collect high spatial and temporal resolution synchronized acoustic and meteorological data. Specifically, the mature configuration includes: a long-range acoustic device capable of source levels up to 140 dB; up to four 7-channel acoustic arrays; two 7-m temperature profiling masts; and a scanning Doppler LIDAR system for volumetric wind profiling at ranges up to several kilometers. This work presents lessons learned over the various iterations of the system such as the design and evolution of the excitation signal used; physical configuration of the components of the system; logistics and planning concerns; post-processing challenges; and quality control considerations.

Acoustic ducting by shelf water streamers at the New England shelfbreak.

Greater sound speed variability has been observed at the New England shelfbreak due to a greater influence from the Gulf Stream with increased meander amplitudes and frequency of Warm Core Ring (WCR) generation. Consequently, underwater sound propagation in the area also becomes more variable. This paper presents field observations of an acoustic near-surface ducting condition induced by shelf water streamers that are related to WCRs. The field observations also reveal the subsequent disappearance of the streamer duct due to the passage of a WCR filament. These two water column conditions are investigated with sound propagation measurements and numerical simulations.

Measurements of sound propagation in Mars' lower atmosphere

Acoustics has become extraterrestrial and Mars provides a new natural laboratory for testing sound propagation models compared to those ones on Earth. Owing to the unique combination of a microphone and two sound sources, the Ingenuity helicopter and the SuperCam laser-induced sparks, the Mars 2020 Perseverance rover payload enables the in situ characterization of unique sound propagation properties of the low-pressure CO2-dominated Mars atmosphere. In this study, we show that atmospheric turbulence is responsible for a large variability in the sound amplitudes from laser-induced sparks. This variability follows the diurnal pattern of turbulence. In addition, acoustic measurements acquired over one Martian year reveal a variation of the sound intensity by a factor of 1.8 from a constant source due to the seasonal cycle of pressure and temperature that significantly modifies the acoustic impedance and shock-wave formation. Finally, we show that the evolution of the Ingenuity tones and laser spark amplitudes with distance is consistent with one of the existing sound absorption models, which is a key parameter for numerical simulations applied to geophysical experiments on CO2-rich atmospheres. Overall, these results demonstrate the potential of sound propagation to interrogate the Mars environment and will therefore help in the design of future acoustic-based experiments for Mars or other planetary atmospheres such as Venus and Titan.

Sound propagation measurements using an autonomous underwater vehicle acoustic array in the New England shelf break acoustics network

The New England shelf break is a highly dynamic region, which experiences complex spatial and temporal water-column variations due to interactions with warm core rings originating from the gulf stream. This widely varying ocean environment leads to changes in sound speed and acoustic propagation. Acoustic payload-equipped autonomous underwater vehicles (AUVs) are advantageous for sound propagation measurements in such environments due to their ability to detect changes with greater spatial resolution compared to fixed moorings. An AUV-towed acoustic array was tested and deployed in the New England Shelf Break Acoustics (NESBA) experiment in May 2021. The acoustic AUV system was comprised of a modified REMUS 600 vehicle, a hull-mounted 3.5 kHz transducer, and a towed multi-channel linear hydrophone array. The AUV sound source was tested at the Dodge Pond Naval Facility to characterize the effect of AUV body resonance, and the resulting calibration was incorporated into the data processing. Propagation paths between the AUV, acoustic moorings, and a ship-towed sound source were studied to investigate the acoustic effects of varying physical oceanographic conditions and biological scattering layers. These measurements also enabled investigation of the local seabed conditions and sub-bottom layering structure. [Work supported by the Office of Naval Research.]

Graduate programs in physical, engineering, and underwater acoustics at the Naval Postgraduate School

The Departments of Physics and of Electrical and Computer Engineering at the Naval Postgraduate School offer graduate programs in acoustics leading to MS and PhD degrees in applied physics and engineering acoustics. Engineering acoustics degrees can be completed in either traditional or distance learning modes. The departments also offer stand-alone academic certificate programs in fundamentals of engineering acoustics, underwater acoustics, and sonar system applications, with a set of three certificates leading to a MS degree in engineering acoustics. MS and PhD programs are interdisciplinary, with courses and laboratory work drawn principally from the fields of physics and electrical engineering. Subjects covered include waves and oscillations; fundamentals of physical and structural acoustics; the generation, propagation, and reception of sound in the ocean; civilian and military applications of sonar systems; and acoustic signal processing. Topics of recent theses and dissertations include development and field testing of novel sensors for atmospheric and ocean acoustics, modeling and measurements of ambient noise and sound propagation in the ocean, sound scattering in underwater waveguides, acoustic vector sensors and vector field properties, acoustic communications, noise interferometry, time reversal in acoustics, geo-acoustic inversion, acoustic remote sensing of the ocean, and acoustics of autonomous underwater and aerial vehicles.

Measurement and modeling of sound propagation over continental slope in the South China Sea.

Measurements along two ship tracks were obtained in an experiment to investigate the properties of acoustic propagation over the continental slope in the South China Sea. The measured data show a notable difference in transmission loss about 35 dB as sound crosses different geodesic paths. Numerical simulations indicate that the range and azimuth-dependent geological properties control the level of the transmission loss and lead to this large transmission loss fluctuation. In addition, the model also suggests some small-scale features of horizontal refraction effect caused by irregular topography, but they are not observed in the measured data.

On the Measurement and Simulation of Flow-Acoustic Sound Propagation in Turbochargers

<div class="section abstract"><div class="htmlview paragraph">Most of today’s internal combustion engines are turbocharged by combined radial compressors and turbines for downsizing. This mostly leads to reduced orifice noise of both intake and exhaust systems, but the detailed damping mechanisms remain yet unknown. Intake and exhaust systems are developed with 1D-CFD simulations, but validated acoustic sub-models for turbochargers are not yet available. Therefore the aim of this publication is studying the turbocharger’s silencing capabilities and subsequently develop new acoustic turbocharger models.</div><div class="htmlview paragraph">The acoustic properties of the turbocharger can be well described by transmission loss. In addition to thermodynamic variations, parameter variations with wastegate and VTG systems were also performed. A total of four turbochargers of very different sizes were investigated. Low frequency attenuation is dominated by impedance discontinuities, increasing considerably with mass flow and pressure ratio. High frequency transmission loss is generated by destructive interferences in the stator, which depend on the stator mass flow distribution and the turbocharger size.</div><div class="htmlview paragraph">A new generic turbocharger model was developed to model both low frequency impedance discontinuities and high-frequency interferences by combining a generic geometric housing model with dynamically controlled energy terms and conventional turbocharger maps. The high thermodynamic quality is a necessary prerequisite for the high acoustic accuracy achieved. The model could be validated and the accuracy was increased by as much as 5 dB, especially for higher frequencies of engine noise.</div></div>

Geoacoustic inversion of 3.5-kHz towed receiver data from the KOREX-17

The Korea Reverberation Experiment 2017 (KOREX-17) was conducted in a shallow water located in the south of the Geoje island, Korea. During the experiment, sound propagation measurements were made using a 3.5-kHz CW signal along different 2 tracks to a distance of ~10 km from a bottom-mounted source, ARMS (Autonomous Reverberation Measurement System). The signals were received by a SRH (Self Recording Hydrophone), which was towed at a depth of ~20 m during the measurements. The sound speed profile was almost iso-velocity, and the sediment at the site was mainly composed of silt having a mean grain size of 6 phi. Since the sound propagation in shallow water is greatly influenced by sound interaction with the sediment, geoacoustic inversion was tried using a genetic algorithm based matched field processing in which the measured acoustic pressure field was compared to the simulated field predicted by a parabolic-equation based propagation model (RAM). The results are compared to the geoacoustic parameters obtained by the empirical relationship to mean grain size and a sediment layering information obtained by a chirp sonar survey. [Work supported by Agency for Defense Development, Korea (UD170014DD).]The Korea Reverberation Experiment 2017 (KOREX-17) was conducted in a shallow water located in the south of the Geoje island, Korea. During the experiment, sound propagation measurements were made using a 3.5-kHz CW signal along different 2 tracks to a distance of ~10 km from a bottom-mounted source, ARMS (Autonomous Reverberation Measurement System). The signals were received by a SRH (Self Recording Hydrophone), which was towed at a depth of ~20 m during the measurements. The sound speed profile was almost iso-velocity, and the sediment at the site was mainly composed of silt having a mean grain size of 6 phi. Since the sound propagation in shallow water is greatly influenced by sound interaction with the sediment, geoacoustic inversion was tried using a genetic algorithm based matched field processing in which the measured acoustic pressure field was compared to the simulated field predicted by a parabolic-equation based propagation model (RAM). The results are compared to the geoacoustic parameters ob...

Calculations of low-frequency wind noise along a low two-dimensional hill surface

Measurement of outdoor sound propagation is often limited by wind noise, i.e. pressure fluctuations from atmospheric turbulence, especially for infrasound and low audible frequencies. Over a flat ground surface, the spectral density of wind noise can be predicted by the shear-turbulence mechanism for static pressure fluctuations using a mirror flow atmospheric turbulence model for the inhomogeneous surface-blocking effect. This study moves beyond a flat ground model to consider the effects of flow distortion by weak topography on surface wind noise, specifically, flow over a low two-dimensional hill, free from separation, at large Froude number. The integral solution for the pressure Poisson equation is used as a starting point, with turbulence modeled by the mirror flow in surface-following coordinates. The perturbation analysis of Hunt et al. [Q. J. R. Meteorol. Soc. 114(484), 1435–1470 (1988)] is used to model the mean shear rate as a function of elevation and distance over the hill. For upwind, downwi...

Estimation of sound speed and attenuation in muddy sediments using spatial coherence measurements of sound propagation

In the spring of 2017, a multi-national and multi-institute shallow water propagation experiment was conducted in the New England Mud Patch in order to study the acoustic properties in muddy sediments. Different types of acoustic signals (i.e., 31-g explosive charges, combustive sound source, multi-tone, and linear frequency modulation signals) deployed at various ranges, depths and azimuths were measured by one L-shaped array, one horizontal line array, and several vertical line arrays within the 30 km × 10 km experimental area. In this paper, these measured signals are first utilized to obtain the correlation coefficients for vertical coherence (VC) and longitudinal horizontal coherence (LHC), which are sensitive to the seabed geo-acoustic parameters. These spatial coherence measurements are then applied in the VC and LHC based geo-acoustic inversion algorithms [Wan et. al. JASA, 2016] to infer sound speed and attenuation in muddy sediments. Finally, the results from VC and LHC based geo-acoustic invers...

A comparison between directly measured and inferred wave speeds from an acoustic propagation experiment in Currituck Sound.

An acoustic propagation experiment was conducted in Currituck Sound to characterize low-frequency propagation in a very-shallow-water estuarine environment. The water column properties were homogeneous over the study area, and the emphasis of this work is on understanding the propagation effects induced by the estuarine bed. During the experiment, low-frequency sound propagation measurements of waterborne sound and interface waves were acquired, and direct measurements of the compressional and shear wave properties were obtained at high frequencies. The propagation data consist of signals from a Combustive Sound Source recorded on bottom mounted geophones and a vertical line array of hydrophones. A statistical inference method was applied to obtain an estimate of the sediment compressional and shear wave speed profiles as a function of depth within the estuarine bed. The direct measurements were obtained in situ by inserting probes 30 cm into the sediment. Sediment acoustics models were fit to the high-frequency in situ data to enable comparison with the inferred low-frequency wave speeds. Overall, good agreement was found between the directly measured and inferred wave speeds for both the compressional and shear wave data.

Acoustical characterization of a seagrass meadow in the Lower Laguna Madre

This talk presents preliminary results from an experiment conducted in the Lower Laguna Madre, Texas to characterize the physical and acoustical properties in a meadow of Thalassia testudinum. Concurrent measurements were collected using (1) acoustic probes, (2) side-scan and parametric sonar, (3) broadband propagation, and (4) sediment cores. The acoustic probes provided localized, direct measurements of sound propagation in the seagrass canopy as well as geoacoustic properties (compressional and shear wave speed and attenuation) of the seagrass-bearing sediment. The side-scan and parametric sonars were used to survey for seagrass abundance and sub-bottom layering. Broadband signals produced by a combustive sound source were recorded at several ranges by hydrophones and geophones and were used to infer geoacoustic properties of the seagrass and underlying sediment for rapid environmental assessment. The sediment cores were analyzed in the laboratory using both low-frequency resonator measurements and high frequency travel-time measurements to estimate compressional wave speed, after which they were sectioned and measurements of sediment grain size, porosity, and biomass were obtained. The combination of these data sets provides a unique characterization of the geoacoustic properties of a seagrass meadow. [Work sponsored by ARL:UT IR&D and ONR.]

Effects of atmospheric nonstationarity on models of low-frequency surface wind noise

Measurements of sound propagation in the atmosphere are often limited by wind noise, particularly at low frequencies. The spectrum of wind noise at the ground surface, i.e. turbulent static pressure, can be modeled by the dominant shear-turbulence mechanism within the atmospheric boundary layer. This model assumes statistically-stationary boundary-layer turbulence, and as in the atmospheric sciences, quasi-stationarity is hypothesized to justify the assumption. However, this hypothesis is not uniformly valid, due to the diurnal cycle and large-scale atmospheric dynamics, and should be tested. This study applies several existing tests of nonstationarity to atmospheric measurements from a field experiment near Laramie, Wyoming and characterizes their relevance to simultaneous recordings of wind noise by flush-mounted infrasound sensors. By estimating the parameters for a mirror flow model of boundary-layer turbulence from the anemometer records, surface pressure model spectra are compared with the experimental wind noise. The performance of both the atmospheric turbulence and wind noise models are assessed with respect to each nonstationarity test.

Measurement of atmospheric sound propagation and meteorological parameters to support development of an acoustic propagation model

Acoustic propagation over long distances is affected by many conditions including atmospheric properties, topography, vegetation, source characteristics, and frequency content. This work presents the results of a set of measurements of acoustic propagation of impulsive sound in the low kilohertz frequency range. These measurements are made over flat ground with limited vegetation at propagation ranges of up to 400 m. At multiple locations along the propagation path, the temperature, pressure, and relative humidity, along with altitude and GPS position are recorded to provide high spatial resolution characterization of the air column in the propagation path. A mast-mounted weather station at the acoustic source provides a record of wind speed and direction at ground level. These measurements are intended to inform related efforts developing a model of acoustic propagation that uses a Crank-Nicolson Parabolic Equation implementation. The measured transmission loss will be compared to preliminary results fro...

Seabed attenuation inversion from broadband reverberation measurements in the Yellow Sea

The Yellow Sea 1996 experiment was the first joint China-U.S. shallow water experiment conducted in August, 1996. The water depth is 75 m with a deviation of ±1 m at the experimental area. The seabed sound speed and attenuation in this experiment have been successfully estimated using the sound propagation measurements [Wan, Zhou, and Rogers, J. Acoust. Soc. Am. 128(2), 2010]. During this experiment, the monostatic reverberation data produced by 1-kg TNT shots provide a spatial sampling of the acoustic field and contains the information of seabed acoustic properties. Thus, the present paper uses the inverted seabed sound speed from the aforementioned propagation measurements as a constraint condition and analyzes the reverberation data for seabed attenuation inversion. The broadband normal mode filter is applied to the reverberation data received by a 32-element vertical line array. The reverberation level of the first three modes is obtained as a function of range to extract the modal attenuation coefficients. The seabed attenuation is inferred by minimizing the difference between the theoretical and measured modal attenuation coefficients. The inverted seabed attenuation over a frequency range of 400–1000 Hz shows non-linear frequency dependence.

Laboratory scale measurements of three-dimensional sound propagation in the presence of a tilted penetrable bottom

Results of laboratory-scale measurements of long-range across-slope pulse propagation in three-dimensional wedge-shaped oceanic waveguides with a sandy bottom are reviewed. The experimental data considered were collected during two laboratory-scale experimental campaigns that were led in 2006 and 2007 (after a required calibration phase) in the large indoor shallow-water tank of the LMA-CNRS laboratory in Marseille. Operational frequencies and water depths were chosen to produce a reduced number of propagating modes so as to facilitate the analysis of the received signals. The experimental data contain strong 3-D effects like mode shadow zones and multiple mode arrivals, all consistent with well-known three-dimensional effects described in the literature. The data are compared with numerical solutions obtained using a fully three-dimensional parabolic equation based model. Comparisons are performed in both time domain (received signals at distinct ranges and depths) and frequency domain (TL-versus-range curves at distinct depths for several discrete frequencies). In both cases, the experimental data are in good agreement with the numerical predictions.

Laboratory measurements of sound propagation in a continuously stratified ocean containing internal waves

A tank experiment is being conducted to explore sound propagation in a continuously stratified ocean containing internal gravity waves that produce fluctuations in acoustic signals. The tank is filled with water of increasing salinity with increasing depth in the fluid; the variation in salinity results in a 150 m/s variation of the sound speed over the 50 cm-depth fluid. Sound arrival times determined in three-dimensional hydrophone scans map out the sound diffraction pattern in the stratified fluid. Good agreement is found between the measurements and results obtained from wavefront modeling by ray acoustics. Sound fluctuations produced by internal waves are measured for several acoustic track locations and at different phases of the internal waves that radiate from a mechanical wave generator. Internal wave fields measured by particle image velocimetry provide input for a parabolic equation model, which is used to predict the sound fluctuations for comparison with measurements. This research is designed to improve the understanding and modeling of sound propagation and scattering by internal waves in the realistic oceans. [Research support: The 2013-14 ASA F. V. Hunt Postdoctoral Research Fellowship (L. Zhang) and ONR MURI Grant N000141110701 (WHOI).]

Elastic properties of the titanium alloy Ti-6Al-4V

The manuscript presents results of Young's modulus (E) measurements for two-phase titanium alloy Ti-6Al-4V. The estimation of elasticity modulus (E) was made using three independent methods: standard mechanical tests (tensile test) on an electronic dynamometer “Instron”, the method measurement of sound speed propagation and the method of nanoindentation using nanohardness – testing scanning machine “Nanoscan3D”. The elastic properties were studied for Ti-6Al-4V alloy in different structural states: nanostructured (NS), microcrystalline (MC) and coarse-grained (CG). The elastic modulus α - and β - phases were measured by means of nanoindatation methods. It is shown that a value of elasticity modulus E for the Ti – 6Al – 4V alloy in the CG state is less than in the NS state by more than 20% that is likely to be attributed to the change in amount ratio between α and β phases characterized by different elastic properties.

Magnetic anisotropy and magnetic phase transitions in RFe5Al7

RFe5Al7 (R – Gd, Tb, Dy, Ho, Er and Tm) single crystals have been studied by measurements of magnetization, sound propagation (in static and pulsed magnetic fields up to 60T) and specific heat. Fundamental magnetic properties have been determined and compared for all these materials. RFe5Al7 are highly anisotropic ferrimagnets. Spontaneous and field-induced magnetic phase transitions of anisotropic and exchange nature have been observed in RFe5Al7. Strong magnetoelastic interactions are manifested by pronounced acoustic anomalies at the phase transformations. The detected magnetization jumps provide important information on the R–Fe inter-sublattice exchange interactions.

Characteristics of sound propagation in shallow water over an elastic seabed with a thin cap-rock layer

Measurements of low-frequency sound propagation over the areas of the Australian continental shelf, where the bottom sediments consist primarily of calcarenite, have revealed that acoustic transmission losses are generally much higher than those observed over other continental shelves and remain relatively low only in a few narrow frequency bands. This paper considers this phenomenon and provides a physical interpretation in terms of normal modes in shallow water over a layered elastic seabed with a shear wave speed comparable to but lower than the water-column sound speed. A theoretical analysis and numerical modeling show that, in such environments, low attenuation of underwater sound is expected only in narrow frequency bands just above the modal critical frequencies which in turn are governed primarily by the water depth and compressional wave speed in the seabed. In addition, the effect of a thin layer of harder cap-rock overlaying less consolidated sediments is considered. Low-frequency transmission loss data collected from an offshore seismic survey in Bass Strait on the southern Australian continental shelf are analyzed and shown to be in broad agreement with the numerical predictions based on the theoretical analysis and modeling using an elastic parabolic equation solution for range-dependent bathymetry.