Sound Speed Dispersion Research Articles

Depth and frequency dependence of geoacoustic properties on the New England Mud Patch from reflection coefficient inversiona).

Muddy sediments cover significant portions of continental shelves, but their physical properties remain poorly understood compared to sandy sediments. This paper presents a generally applicable model for sediment-column structure and variability on the New England Mud Patch (NEMP), based on trans-dimensional Bayesian inversion of wide-angle, broadband reflection-coefficient data in this work and in two previously published reflection-coefficient inversions at different sites on the NEMP. The data considered here include higher frequencies and larger bandwidth and cover lower reflection grazing angles than the previous studies, hence, resulting in geoacoustic profiles with significantly better structural resolution and smaller uncertainties. The general sediment-column structure model includes an upper mud layer in which sediment properties change slightly with depth due to near-surface processes, an intermediate mud layer with nearly uniform properties, and a geoacoustic transition layer where properties change rapidly with depth (porosity decreases and sound speed, density, and attenuation increase) due to increasing sand content in the mud above a sand layer. Over the full frequency band considered in the new and two previous data sets (400-3125 Hz), there is no significant sound-speed dispersion in the mud, and attenuation follows an approximately linear frequency dependence.

Study on the effect of seafloor sound speed dispersion on sound propagation

As one of the boundaries of ocean waveguide, the acoustic properties of seafloor sediments have been a hot research problem in ocean acoustic propagation and acoustic field modeling. The existing research has shown that the sound velocity in seafloor sediment is frequency dependent. In order to solve the problem that the sedimentary sound speed dispersing often be ignored in actual applications, this article uses the parabolic Newton to iterate to solve the dispersion equation to obtain the characteristic value of the normal mode. And the impact of frequency dispersion of sediment sound speed through simulation are studied. The results show that the sound wave in the time domain will appear more obvious broadening phenomenon, and the propagation loss will be reduced after considering the sound velocity dispersion of the sediment. Also, with the increase of frequency, the more obvious the effect of sound velocity dispersion on the sound propagation in the frequency range of sound velocity dispersion.

Derivation of acoustical streaming equations for nonlinear and dispersive fluids

The equations of streaming generated by an acoustic mod propagating in a nonlinear dispersive medium (exhibiting absorption and dispersion of phase sound speed) are derived with an arbitrarily shaped incident acoustical field assumed. This field may be periodic or non-periodic. A general dispersion model represented by a convolution operator taking into account relaxation effects was taken into account. Making the assumption of a periodic acoustic field from the general streaming equation.The quasi-stationary flow is driven by a force given by the average value of the dispersion operator with respect to the velocity and acoustic pressure fields. In the spectral representation, it is given by the weighted spectral power density distribution of the acoustic field. The weight of the distribution is the dispersion coefficient - the eigenvalue of the dispersion operator. A new result also reveals the effect of the refractive index deviation on the driving force of streaming. The possibility of generalizing the description of streaming in the simplest case of a non-Newtonian fluid was analyzed. The Reiner-Revlin model of a simple liquid was assumed. It was also noted that the streaming model in the Maxwell liquid is analytically solvable. It was found that asymptotic states of streaming in this model and the Navier-Stokes model are identical.The derivations use new methods different from those used so far. They are based on the separation of nonlinear modes in the momentum transport equation and on the properties of the Gauss-Weierstrass function for the Fick diffusion operator. So far, the method of successive approximations has been used. The consistency of the obtained equations with the assumptions was checked. The obtained formulas generalize the known descriptions of the form of forces driving streaming and extend their application to the case of nonlinear propagation.

Identifying gas composition based on the decomposed relaxation strength from sound-speed dispersion

Measuring the sound-speed dispersion in excitable gases demonstrates its potential for gas detection owing to its low measurement error. However, identifying the gas composition of a multi-component gas mixture remains a challenge in this method. The relaxation strength of the gas mixture determines the change in speed dispersion and depends on the gas composition. In this paper, we propose a method for identifying the gas composition based on relaxation strength. First, we extracted the decomposed relaxation strength from sound-speed dispersion and clarified the contribution of individual gas component to the decomposed relaxation strength. Second, we identified the gas composition by the relative change in the decomposed relaxation strength due to the variation in the environment temperature, and calculate the gas concentration by the ratio of the decomposed relaxation strength to the relaxation strength of the corresponding pure gas. Thus, complete identification can be performed for a multi-component gas mixture using the proposed method. For gas mixtures containing CO2,CH4 and N2, the simulations and experimental results validated the robustness and effectiveness of the proposed method.

High-Frequency Dependence of Acoustic Properties of Three Typical Sediments in the South China Sea

The acoustic characteristics of three fine-grained sediments (silty sand, silt, silty clay) in the South China Sea (SCS) were measured and analyzed at high frequency range of 27–247 kHz. The measurement results show that the sound speed dispersion is a positive linear relation at the measured frequency range, and the attenuation follows nonlinear frequency dependence, α = kfn, where n ranges from 0.59 to 0.85 for the three different sediments in the SCS. The frequency dependence of sound speed and attenuation were compared with the published literature. It was found that for silty clay, clayey silt, silt, and silty sand, the dispersion characteristics of these four sediments are basically consistent; in general, the dispersion of coarse particles is significant, and that of fine particles is weak, and permeability is the key parameter that determines the inflection point of high frequency to low frequency. By modeling these sediments with the Biot–Stoll model, it was found that the Biot–Stoll model can better predict the frequency-dependent characteristics of sound attenuation in a high-frequency band under the matching constraints of sound speed dispersion characteristics, indicating that the Biot–Stoll model has good applicability to different types of sediments in a high-frequency band.

Statistical Inference of Sound Speed and Attenuation Dispersion of a Fine-Grained Marine Sediment

Acoustic recordings of signals in the 1.5–4.0-kHz band were analyzed for information about the sound speed and attenuation frequency dispersion of a fine-grained sediment found in the New England Mudpatch. Analysis of piston cores established prior bounds for a geophysical parameterization of a seabed model that predicts Kramers–Kronig dispersion relations. Sediment layers are described by the Buckingham viscous grain shearing (VGS) model that accounts for the effects of overburden pressure of compressional and shear speeds and attenuations. A statistical inverse problem was solved by using multiple samples of received levels recorded on two vertical line arrays as a function time and hydrophone depth for six frequencies in the 1.5–4.0-kHz band. A statistical inference model that assumed both model parameters and data samples are random variables quantified information content from marginalization of a conditional posterior probability distribution for the geophysical parameters that characterize the mud layer. From the inferred geophysical parameter point estimates the sediment sound speed and attenuation frequency dispersion are predicted and compared to previously reported direct measurements. Also, the predicted sound-speed gradient in the mud sediment from the VGS model is compared to a previous inference that utilized explosive sources.

Synthesizing the frequency-dependent sound relaxational absorption by three-frequency sound speeds in excitable gases

Capturing the frequency-dependent sound relaxational absorption in excitable gases has the potential of wide applications in gas detection; however, it is still challenging to accurately measure it in real time. With the aid of the relationship between effective compression coefficient and acoustic relaxation process, an approach to synthesize the frequency-dependent sound relaxational absorption is proposed by using the sound speeds at three frequencies under a single pressure that are far easier to be precisely measured in real time. The proposed approach includes three steps. Firstly, the relaxation strength is calculated from the low-frequency and the high-frequency sound speeds measured at two selected frequencies; secondly, the adiabatic constant pressure relaxation time is calculated from the sound speed measured at the third frequency within the range where the sound relaxational absorption is significant; finally, the frequency-dependent sound relaxational absorption and sound speed dispersion are synthesized by the real and imaginary parts of the normalized high-frequency effective adiabatic coefficient. For gases containing CH4, CO2, CL2 and N2, the synthesized results are consistent with the experimental data. Our approach provides a real-time acoustic solution with higher accuracy and implementation convenience for gas detecting.

High frequency dependence of sound speed and attenuation in coral sand sediments

The acoustic properties of seafloor coral sand sediments are of significant meaning for accurately modeling underwater sound propagation in sea areas around coral reef islands. To ultrasonically measure coral sand sediments with different grain sizes, sediment samples from coral islands were screened and remolded into five types of samples with different grain sizes. This study measured the sound speed and attenuation in the frequency range of 27–247 kHz and analyzed the frequency dependence of the acoustic properties. The results showed that the sound speed increased significantly with frequency, suggesting an approximately linear relation. The sound speed dispersion in the coarse-grained sediments was larger than that in the fine-grained sediments. The measured attenuation data showed a variable frequency dependence among the different sediment types. The measured data were compared with Biot-Stoll model (BS model) predictions, and the fitting results showed that intergranular pores can lead to sound speed data-model mismatches. The attenuation data-model comparisons revealed that sediments with different grain sizes have different sound wave energy loss mechanisms. The BS model with grain contact squirt flow and shear drag (BICSQS model) can match the attenuation data more consistently than the BS model. The results show that scattering is an important factor in sound attenuation in coral sand sediment and the attenuation scattering factors for different grain size sediments were provided.

Analytical relationship between sound relaxational absorption and sound speed dispersion in excitable gases

Analytical relationship between sound relaxational absorption and sound speed dispersion in excitable gases

Key role of retardation and non-locality in sound propagation in amorphous solids as evidenced by a projection formalism.

We investigate acoustic propagation in amorphous solids by constructing a projection formalism based on separating atomic vibrations into two, "phonon" (P) and "non-phonon" (NP), subspaces corresponding to large and small wavelengths. For a pairwise interaction model, we show the existence of a "natural" separation lengthscale, determined by structural disorder, for which the isolated P subspace presents the acoustic properties of a nearly homogenous (Debye-like) elastic continuum, while the NP one encapsulates all small scale non-affinity effects. The NP eigenstates then play the role of dynamical scatterers for the phonons. However, at variance with a conjecture of defect theories, their spectra present a finite low frequency gap, which turns out to lie around the Boson peak frequency, and only a small fraction of them are highly localized. We then show that small scale disorder effects can be rigorously reduced to the existence, in the Navier-like wave equation of the continuum, of a generalized elasticity tensor, which is not only retarded, since scatterers are dynamical, but also non-local. The full neglect of both retardation and non-locality suffices to account for most of the corrections to Born macroscopic moduli. However, these two features are responsible for sound speed dispersion and have quite a significant effect on the magnitude of sound attenuation. Although it remains open how they impact the asymptotic, large wavelength scaling of sound damping, our findings rule out the possibility of representing an amorphous solid by an inhomogeneous elastic continuum with the standard (i.e., local and static) elastic moduli.

Assessing The Influence of Internal and Viscous Friction on Dispersion and Sound Attenuation in Unconsolidated Marine Sediments

The study analyzes influence of internal and viscous dissipation on sound propagation of in unconsolidated marine sediments. The main provisions of M. Buckingham’s GS theory of intergranular friction are presented. According to GS theory, sediments are considered as a single-phase medium, sound attenuation is explained by internal friction alone, and viscous dissipation is neglected. A modification of GS theory is presented, which transforms it to two-phase. Instead of a single-phase equation of state, an equation of state of a two-phase medium is applied, previously derived in a study by work I.A. Chaban. Substitution of this equation of state into the dispersion relation of GS theory leads to a quadratic equation, the roots of which give the wavenumbers of two types of waves, fast and slow, in an unconsolidated medium with internal friction (GS + EC, grain shearing + effective compressibility). The results given by the modified theory are compared with the results of experimental measurements taken from open sources. It is shown that significant sound speed dispersion at medium frequencies results from the conservative influence of the fluid, and attenuation, from the combined dissipative effect of internal and viscous losses. The types of media and frequency ranges are revealed in which attenuation is determined mainly by the forces of internal or viscous friction.

On the sound speed dispersion and the frequency dependence of sound attenuation in a fine-grained sediment in the New England Mud Patch

The study on the sound speed dispersion and the frequency dependence of sound attenuation in marine sediments is of great importance in understanding the physics of sound propagation in the sea bottom. Modal dispersion curves (MDC) have only been utilized to estimate the low-frequency sound speed. At higher frequencies (i.e., above a few hundred hertz), arrival time difference for different modes generally become smaller and MDC is difficult to extract because of the cross-mode interference. This paper applies time-frequency representations (TFR) with high time-frequency resolution (e.g., optimal-kernel and center-affine-filtered TFR) to broadband acoustic signals (e.g., 31g explosive and combustive source signals) detonated along the 15-km Northwest-Southeast tracks during the Seabed Characterization Experiment in the New England Mud Patch, which has a surface fine-grained sediment layer overlying a sandy bottom. The resulting high-resolution broadband (150–1500 Hz) MDC, in conjunction with TL data, are fed to a previously developed two-step dimension-reduced geoacoustic inversion algorithm including modal dispersion-based inversion for sound speed and energy-based inversion for attenuation [IEEE J. Ocean. Eng., 44, in print, (2019)]. The estimated sound speed and attenuation are compared with the theoretical results from seabed geoacoustic models for fine-grained sediments. [Work supported by ONR Ocean Acoustics (322OA).]The study on the sound speed dispersion and the frequency dependence of sound attenuation in marine sediments is of great importance in understanding the physics of sound propagation in the sea bottom. Modal dispersion curves (MDC) have only been utilized to estimate the low-frequency sound speed. At higher frequencies (i.e., above a few hundred hertz), arrival time difference for different modes generally become smaller and MDC is difficult to extract because of the cross-mode interference. This paper applies time-frequency representations (TFR) with high time-frequency resolution (e.g., optimal-kernel and center-affine-filtered TFR) to broadband acoustic signals (e.g., 31g explosive and combustive source signals) detonated along the 15-km Northwest-Southeast tracks during the Seabed Characterization Experiment in the New England Mud Patch, which has a surface fine-grained sediment layer overlying a sandy bottom. The resulting high-resolution broadband (150–1500 Hz) MDC, in conjunction with TL data, are ...

Research on the sediment acoustic properties based on a water coupled laboratory measurement system

The high-frequency acoustic properties of seafloor sediments are very significant in seafloor study and underwater acoustic study field. In order to measure the sound speed and the attenuation for the small-scale sediment cores more accurately, this study developed a water coupled acoustic laboratory measurement system based on Richardson-Briggs technique. This method used the correlation comparison of waveforms received in sediment core and in identical reference tubes filled with water to measure sound speed and attenuation. The sound speed and attenuation of a clayey silt sediment sample were measured using the water coupled acoustic laboratory measurement system. This frequency dependence of the sound speed and attenuation showed that the clayey silt sediment has a weak positive sound speed dispersion, while the attenuation increases with a strong positive gradient within the measurement frequency range. This study also noted that the measured sound speed ratio match well with the empirical equations from literature. The measured attenuation factor data can fall in the Hamilton’s empirical prediction range.

A micro-mechanical model for the Biot theory of acoustic waves in a fully saturated granular material

In the context of the classical Biot theory for acoustic waves in a fully-saturated granular material, we improve upon the constitutive relation of the solid phase by means of micro-mechanical modeling. This is needed to explain discrepancies on the dependency of the frequency with the sound speed attenuation and dispersion between present models and experiment. As first step, we provide a more detailed description of the interaction between the particles and water. A Standard Linear Solid model is proposed to represent the behavior at contact level between particles immersed in a compressible fluid.

Frequency dependence of sound speed and attenuation in fine-grained sediments from 25 to 250 kHz based on a probe method

The frequency dependence of the sound speed and attenuation in seafloor sediments was measured in a laboratory by using a probe method at the frequency range of 25–250 kHz. The standard deviation of repeated sound speed measurement in fresh water is about 2.82 m/s. Repeated measurement of attenuation shows a minimum standard deviation of 0.58 dB at 25 kHz and a maximum standard deviation of 3.06 dB/m at 250 kHz. The measurement results indicate that the sound speeds vary from 1638 to 1658 m/s in sandy silt sediments and from 1548 to 1571 m/s in clayey silt sediments. The attenuation increases from 14.2 to 51.9 dB/m in sandy silt sediments and from 7.8 to 31.7 dB/m in clayey silt sediments. The measured sound speed dispersion in sandy silt sediment agrees reasonably with the predictions of the Biot-Stoll model, the Grain-Shearing model, and the Effective Density Fluid model (EDFM). The measured sound speed in clayey silt sediment agrees better with the predictions of the GS model than that of the Biot-Stoll model and the EDFM. The measured attenuation is more consistent with f1/2 dependence than the f1 dependence, and is similar to the predictions of Biot-Stoll model and the EDFM.

Estimating low-frequency sediment sound speed dispersion from the horizontal coherence of the head wave excited by a light helicopter

A series of shallow-water acoustic experiments has been conducted off the coast of southern California using a Robinson R44 helicopter as a low-frequency (≈ 13–3500 Hz) sound source. The aim of the experiments was to recover the sound speed of a fine to very-fine sand sediment from the horizontal coherence of the head wave excited in the water column by the helicopter. Two hydrophones, separated horizontally by approximately 15 m and situated 0.5 m above the seabed, received the head-wave signals, allowing the coherence function to be formed over the bandwidth of the airborne source. The sediment sound speed was recovered by matching the zero crossings of the measured coherence function to those predicted from a recently developed theory of head-wave generation in shallow water. Using this technique, the dispersion in the sediment sound speed can be estimated over a frequency range extending between 27 Hz, the lowest zero crossing of the coherence function, and 3.5 kHz, the bandwidth of the source. In the middle of the frequency band, the sound speed of the sediment was estimated to be 1682 ± 16 m/s, consistent with the known sediment type. [Research supported by ONR, SMART(DOD), NAVAIR, and SIO.]A series of shallow-water acoustic experiments has been conducted off the coast of southern California using a Robinson R44 helicopter as a low-frequency (≈ 13–3500 Hz) sound source. The aim of the experiments was to recover the sound speed of a fine to very-fine sand sediment from the horizontal coherence of the head wave excited in the water column by the helicopter. Two hydrophones, separated horizontally by approximately 15 m and situated 0.5 m above the seabed, received the head-wave signals, allowing the coherence function to be formed over the bandwidth of the airborne source. The sediment sound speed was recovered by matching the zero crossings of the measured coherence function to those predicted from a recently developed theory of head-wave generation in shallow water. Using this technique, the dispersion in the sediment sound speed can be estimated over a frequency range extending between 27 Hz, the lowest zero crossing of the coherence function, and 3.5 kHz, the bandwidth of the source. In the...

Sound speed dispersion characteristics of three types of shallow sediments in the southern yellow sea

ABSTRACTTo accurately characterize sound speed dispersion of shallow sediments in the Southern Yellow Sea, three types of sediments, i.e., silt, clayey silt, and silty clay, were selected to measure the sound speeds at 25–250 kHz. Over the frequency range, the sound speeds vary approximately from 1,536 to 1,565 m s−1 in silt sediment, from 1,511 to 1,527 m s−1 in clayey silt sediment, and from 1,456 to 1,466 m s−1 in silty clay sediment. The sound speed exhibits a slow increase with frequency in a nearly linear gradient, but these three types of sediments have different sound speed dispersion characteristics. The silt sediment with relatively coarse grains has the most significant sound speed dispersion, while the sound speed dispersions of the two others are relatively weak. Comparison between the measured dispersions and the model predictions shows that the grain-shearing model can match the measured data at most of frequencies. Nevertheless, when the grain bulk modulus was assigned 3.2 × 1010 Pa according to relevant references, the Biot–Stoll model predictions were higher than the measured values at high frequencies; when it was assigned a relatively small value of 2.8 × 1010 Pa, the model predictions achieved optimal matching with the measured values.

Laboratory measurements of sound speed and attenuation dispersion in calcareous sediments from coral reefs

The calcareous sediment is an important type seafloor sediment exist in coral reef island sea areas. The acoustic properties of calcareous sediment are significant for modeling sound propagation and underwater reverberation. In order to analyze the frequency dependence of sound speed and attenuation in calcareous sediments, the sediments were firstly screened and remodeled in plexiglass tubes in laboratory, and the sound speed and attenuation were measured at the frequency range of 27–247 kHz. The grain sizes of sediment samples were <0.075 mm, 0.075-0.5 mm, 0.5-1 mm, 1–2 mm, and 2–4 mm, respectively. The sound speeds of different grain-size sample were 1564.83–1607.36 m/s, 1564.82–1607.36 m/s, 1527.76–1553.69 m/s, 1529.40–1594.72 m/s, and 1541.87–1596.51 m/s, respectively. The attenuation were 24.94–206.35 dB/m, 20.78–208.75 dB/m, 9.66–271.94 dB/m, 12.33–310.36 dB/m, and 12.60–293.60 dB/m, respectively. The sound speeds and attenuation were found to increase remarkable with frequency. The fine grained sediments have higher sound speed than the coarser sediments, which due to the higher bulk density and lower porosity of fine grained sediments. The dispersion gradients of sound speed and attenuation in coarser sediments were more remarkable than that in fine-grained sediments, which may due to the higher tortuosity of coarser sediments.

Sediment sound speed dispersion inferences from broadband reflection coefficient measurements

The frequency dependence, or dispersion, of sound speed in marine sediments has been a topic of considerable interest and remains a research topic. While experiments on well-sorted sediments (having a narrow range of grain sizes) show promising concordance with theory, the more typical continental shelf sediments exhibit a rather wide range of grain sizes. A major experimental challenge is to measure in-situ sound speed over a sufficiently wide frequency range, such that the underlying mechanisms (e.g., viscous or friction) that control intrinsic dispersion can be isolated. Broadband 1.8-10 kHz seabed reflection measurements in the TREX13 experiment show a critical angle that is very nearly frequency independent. When effects of wavefront curvature, sound speed gradients, layering, and roughness are taken into account, this observation indicates that sediment sound speed must also be nearly independent of frequency. [Research supported by the ONR Ocean Acoustics Program.]

Study on sound-speed dispersion in a sandy sediment at frequency ranges of 0.5–3 kHz and 90–170 kHz

In order to study the properties of sound-speed dispersion in a sandy sediment, the sound speed was measured both at high frequency (90–170 kHz) and low frequency (0.5–3 kHz) in laboratory environments. At high frequency, a sampling measurement was conducted with boiled and uncooked sand samples collected from the bottom of a large water tank. The sound speed was directly obtained through transmission measurement using single source and single hydrophone. At low frequency, an in situ measurement was conducted in the water tank, where the sandy sediment had been homogeneously paved at the bottom for a long time. The sound speed was indirectly inverted according to the traveling time of signals received by three buried hydrophones in the sandy sediment and the geometry in experiment. The results show that the mean sound speed is approximate 1710–1713 m/s with a weak positive gradient in the sand sample after being boiled (as a method to eliminate bubbles as much as possible) at high frequency, which agrees well with the predictions of Biot theory, the effective density fluid model (EDFM) and Buckingham’s theory. However, the sound speed in the uncooked sandy sediment obviously decreases (about 80%) both at high frequency and low frequency due to plenty of bubbles in existence. And the sound-speed dispersion performs a weak negative gradient at high frequency. Finally, a water-unsaturated Biot model is presented for trying to explain the decrease of sound speed in the sandy sediment with plenty of bubbles.