Measurement of Low-Frequency Sound Attenuation in Marine Sediment
TL;DR: In this paper, an experimental method for estimating marine sediment attenuation at low frequencies in shallow water was proposed, where the experimental geometry is short range between a vertical line array and multiple source depths to cover bottom reflections over a wide span of grazing angles.
Abstract: Marine sediment compressional wave attenuation and its frequency dependence have been active topics in the ocean acoustics community. To support the predictions of the frequency dependence of the sediment attenuation, experimental studies are essential for providing the observations of the sediment attenuation as a function of frequency in different environments, such as sediment type, source-receiver range, water depth, etc. This paper proposes an experimental method for estimating marine sediment attenuation at low frequencies in shallow water. The experimental geometry is short range between a vertical line array and multiple source depths to cover bottom reflections over a wide span of grazing angles. Single bounce bottom-reflected (BR) and sub-bottom-reflected signals are used in the analysis to obtain the best approximation of the sediment intrinsic attenuation. The attenuation estimating method is demonstrated on chirp data (1.5-4.5 kHz) collected on the New Jersey Continental Shelf during the 2006 Shallow Water Experiment (SW06). The data indicate a linear frequency dependence of the compressional wave attenuation for clay rich sediments on the outer shelf, and the estimated value is 0.15 dB/? within the frequency band of 1.75-3.15 kHz. The observation of small sound-speed dispersion of ~ 15 m/s over the frequency band is consistent with a linear frequency dependence of attenuation.
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TL;DR: In this article, an acoustic wave equation for pressure accounting for viscoelastic attenuation is derived from visco-elastic equations of motion, assuming that the relaxation moduli are completely monotonic (CM).
Abstract: An acoustic wave equation for pressure accounting for viscoelastic attenuation is derived from viscoelastic equations of motion. It is assumed that the relaxation moduli are completely monotonic (CM). The acoustic equation differs significantly from the equations proposed by Szabo (1994) and in several other papers. Integral representations of dispersion and attenuation are derived. General properties and asymptotic behavior of attenuation and dispersion in the low and high-frequency range are studied. The results are compatible with experiments. The relation between the asymptotic properties of attenuation and wavefront singularities is examined. The theory is applied to some classes of viscoelastic models and to the quasi-linear attenuation reported in seismology.
17 citations
30 Sep 2021
TL;DR: In this article, the progress in geoacoustic inversion over the past several decades is reviewed, and a review is separated into two parts: the first part reviews developments in model-based inversion methods, and the second part reviews the development in geo-acoustic models.
Abstract: This paper reviews the progress in geoacoustic inversion over the past several decades. The review is separated into two parts. The first part reviews developments in model-based inversion methods ...
13 citations
TL;DR: This paper utilizes acoustic normal mode dispersion curves, mode shapes, and modal-based longitudinal horizontal coherence to define a three-objective optimization problem for geoacoustic parameter estimation to applied to long-range combustive sound source data obtained from L-shaped arrays deployed on the New Jersey continental shelf.
Abstract: When using geoacoustic inversion methods, one objective function may not result in a unique solution of the inversion problem because of the ambiguity among the unknown parameters. This paper utilizes acoustic normal mode dispersion curves, mode shapes, and modal-based longitudinal horizontal coherence to define a three-objective optimization problem for geoacoustic parameter estimation. This inversion scheme is applied to long-range combustive sound source data obtained from L-shaped arrays deployed on the New Jersey continental shelf in the summer of 2006. Based on the sub-bottom layering structure from the Compressed High-Intensity Radiated Pulse reflection survey at the experimental site, a two-layer (sand ridge overlaying a half-space basement) range-independent sediment model is utilized. The ambiguities of the sound speed, density, and depth of the sand ridge layer are partially removed by minimizing these objective functions. The inverted seabed sound speed over a frequency range of 15–170 Hz is comparable to the ones from direct measurements and other inversion methods in the same general area. The inverted seabed attenuation shows a nonlinear frequency dependence expressed as αb=0.26f1.55(dB/m) from 50 to 500 Hz or αb=0.32f1.65(dB/m) from 50 to 250 Hz, where f is in kHz.
12 citations
TL;DR: In this article, a matched field inversion (MFI) was used to estimate the sediment/bottom parameters using a moving source and single receiver using a synthetic horizontal line array (SHLA).
Abstract: A midfrequency (2–6 kHz) geoacoustic parameter inversion approach is proposed using a moving source and single receiver. The source motion creates a synthetic horizontal line array (SHLA), and the received signals, by source–receiver reciprocity, can be used to estimate the sediment/bottom parameters using matched field inversion (MFI). Using a wideband signal, the arrival times of multipaths are estimated using compressive sensing, from which one can estimate the source–receiver range, water depth, sediment thickness, and sound speed. This information is difficult to get at low frequencies due to the limited bandwidth. MFI is carried out using the frequency-coherent cost function and does not require the data to be precisely synchronized. Sensitivities of inversion of geoacoustic parameters are also studied. Performance using the SHLA is shown to be comparable to that using the conventional horizontal and vertical line array, and is shown to be sensitive to sediment attenuation—one of the difficult parameters to estimate. The proposed scheme uses short range (50–150 m) data, and requires a low-level source that can be carried by an autonomous underwater vehicle (AUV). With the AUV traveling between nodes in a distributed sensors network, the inversion can be conducted over a large area.
6 citations
Cites background or methods from "Measurement of Low-Frequency Sound ..."
..., sBR) on a vertical or horizontal array [13], [14]....
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...[4]–[7], or horizontal linear array (HLA) [8]–[12] deployed at a distance (kilometers) from the source, using methods such as matched field inversion (MFI) [1], [2], [8]–[11], broadband arrival times analysis [6], [13], [14], and modal dispersion techniques [3], [15], etc....
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TL;DR: The first attempt of an experimental benchmark of geo-acoustic inversion methods was made in this paper, where the authors focused on data from experiments carried out at a common site during the shallow water 2006 (SW06) experiment.
Abstract: Over the past 25 years, there has been significant research activity in development and application of methods for inverting acoustical field data to estimate parameters of geoacoustic models of the ocean bottom. Although the performance of various geoacoustic inversion methods has been benchmarked on simulated data, their performance with experimental data remains an open question. This article constitutes the first attempt of an experimental benchmark of geoacoustic inversion methods. To do so, the article focuses on data from experiments carried out at a common site during the Shallow Water 2006 (SW06) experiment. The contribution of the article is twofold. First, the article provides an overview of experimental inversion methods and results obtained with SW06 data. Second, the article proposes and uses quantitative metrics to assess the experimental performance of inversion methods. From a sonar performance point of view, the benchmark shows that no particular geoacoustic inversion method is definitely better than any other of the ones that were tested. All the inversion methods generated adequate sound-speed profiles, but only a few methods estimated attenuation and density. Also, acoustical field prediction performance drastically reduces with range for all geoacoustic models, and this performance loss dominates over intermodel variability. Overall, the benchmark covers the two main objectives of geoacoustic inversion: obtaining geophysical information about the seabed, and/or predicting acoustic propagation in a given area.
4 citations
Cites background from "Measurement of Low-Frequency Sound ..."
...MF [18], [19] (black); Turgut [23] (blue)....
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...5, along with the midfrequency measured values by Jiang and Jiang and Chapman [19] and Turgut [23] obtained from spectral ratio data....
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...modal group velocity inversion [15]–[17], and travel time inversion [18] and [19]....
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...MF [18] and [19], Turgut [23], Yang et al....
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...[18] and Jiang and Chapman [19] and Choi et al....
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References
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TL;DR: In this article, a theory for the propagation of stress waves in a porous elastic solid containing compressible viscous fluid is developed for the lower frequency range where the assumption of Poiseuille flow is valid.
Abstract: A theory is developed for the propagation of stress waves in a porous elastic solid containing compressible viscous fluid. The emphasis of the present treatment is on materials where fluid and solid are of comparable densities as for instance in the case of water‐saturated rock. The paper denoted here as Part I is restricted to the lower frequency range where the assumption of Poiseuille flow is valid. The extension to the higher frequencies will be treated in Part II. It is found that the material may be described by four nondimensional parameters and a characteristic frequency. There are two dilatational waves and one rotational wave. The physical interpretation of the result is clarified by treating first the case where the fluid is frictionless. The case of a material containing viscous fluid is then developed and discussed numerically. Phase velocity dispersion curves and attenuation coefficients for the three types of waves are plotted as a function of the frequency for various combinations of the characteristic parameters.
7,172 citations
"Measurement of Low-Frequency Sound ..." refers methods in this paper
...Corresponding representative theories are from Hamilton and Buckingham [1], [2] (linear) and Biot [3], [4] (nonlinear)....
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TL;DR: Geoacoustic models of the sea floor are basic to underwater acoustics and to marine geological and geophysical studies of the earth's crust, including stratigraphy, sedimentology, geomorphology, structural and gravity studies, geologic history, and many others as mentioned in this paper.
Abstract: Geoacoustic models of the sea floor are basic to underwater acoustics and to marine geological and geophysical studies of the earth’s crust, including stratigraphy, sedimentology, geomorphology, structural and gravity studies, geologic history, and many others A ’’geoacoustic model’’ is defined as a model of the real sea floor with emphasis on measured, extrapolated, and predicted values of those properties important in underwater acoustics and those aspects of geophysics involving sound transmission In general, a geoacoustic model details the true thicknesses and properties of sediment and rock layers in the sea floor A complete model includes water‐mass data, a detailed bathymetric chart, and profiles of the sea floor (to obtain relief and slopes) At higher sound frequencies, the investigator may be interested in only the first few meters or tens of meters of sediments At lower frequencies information must be provided on the whole sediment column and on properties of the underlying rocks Complete geoacoustic models are especially important to the acoustician studying sound interactions with the sea floor in several critical aspects: they guide theoretical studies, help reconcile experiments at sea with theory, and aid in predicting the effects of the sea floor on sound propagation The information required for a complete geoacoustic model should include the following for each sediment and rock layer In some cases, the state‐of‐the‐art allows only rough estimates, in others information may be nonexistent (1) Identification of sediment and rock types at the sea floor and in the underlying layers (2) True thicknesses and shapes of layers, and locations of significant reflectors (which may vary with sound frequencies) For the following properties, information is required in the surface of the sea floor, in the surface of the acoustic basement, and values of the property as a function of depth in the sea floor (3) Compressional wave (sound) velocity (4) Shear wave velocity (5) Attenuation of compressional waves (6) Attenuation of shear waves (7) Density (8) Additional elastic properties (eg, dynamic rigidity and Lame’s constant); given compressional and shear wave velocities and density, these and other elastic properties can be computed There is an almost infinite variety of geoacoustic models; consequently, the floor of the world’s ocean cannot be defined by any single model or even a small number of models; therefore, it is important that acoustic and geophysical experiments at sea be supported by a particular model, or models, of the area However, it is possible to use geological and geophysical judgement to extrapolate models over wider areas within geomorphic provinces To extrapolate models requires water‐mass data (such as from Nansen casts and velocimeter lowerings), good bathymetric charts, sediment and rock information from charts, cores, and the Deep Sea Drilling Project, echo‐sounder profiles, reflection and refraction records (which show detailed and general layering and the location of the acoustic basement), sound velocities in the layers, and geological and geophysical judgement Recent studies have provided much new information which, with older data, yield general values and restrictive parameters for many properties of marine sediments and rocks These general values and parameters, and methods for their derivation, are the main subjects of this paper
885 citations
TL;DR: In this paper, a unified theory of sound propagation in saturated marine sediments is developed on the basis of a linear wave equation, which includes a new dissipation term representing internal losses arising from interparticle contacts.
Abstract: A unified theory of sound propagation in saturated marine sediments is developed on the basis of a linear wave equation, which includes a new dissipation term representing internal losses arising from interparticle contacts. This loss mechanism, which shows a “memory” or hysteresis, is proposed as being responsible for the acoustic properties of sediments. To accommodate the memory, the loss term in the wave equation is formulated as a temporal convolution between the particle velocity and a material response function, h(t), which varies as t−n, where 0
170 citations
"Measurement of Low-Frequency Sound ..." refers methods in this paper
...Corresponding representative theories are from Hamilton and Buckingham [1], [2] (linear) and Biot [3], [4] (nonlinear)....
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TL;DR: In this article, nearly 100 collocated grab samples and in situ 65 kHz acoustic measurements were collected on the New Jersey middle and outer shelf within an area that had previously been mapped with multibeam backscatter and bathymetry data, and more recently with chirp seismic reflection profiling.
169 citations
TL;DR: The Oceanography 20, 4, 4 (2007): 156-167 as mentioned in this paper is the most cited work in this category and is published by the Oceanography Society (OS) for personal use.
Abstract: Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 4 (2007): 156-167.
145 citations