Acoustic scattering in the ocean from velocity and density fluctuations in the sediments

Yamamoto, Tokuo

doi:10.1121/1.414662

Cited by 54 publications

(29 citation statements)

References 17 publications

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“…Traditionally, Gaussian and exponential correlation functions have often been used because of their mathematical simplicity (14,33,35]. Recently, a power-law type of correlation function has attracted more interest [53,63]. Meanwhile, Yamamoto, in his measurement of velocity variability using crosswell acoustic tomography, found the measured power spectra approximate a power law [64].…”

Section: Correlation Functions Of Sound Speed Variationsmentioning

confidence: 99%

“…Recently, Yamamoto [39] used the same approach as Chernov's [33) to model density and sound speed fluctuations in the sediment. The above fluctuations were described by a power law distribution and the parameters were estimated from crosswen tomography.…”

Section: Morse and Ingardmentioning

confidence: 99%

“…The necessity to include pore-elastic effects in t he scattering model remains an open question [18], and we will regard the bottom as an acoustic fluid. The free-space Green's function, together with the transmission coefficient at the water/bottom interface has been used in some work [24,53]. Despite its simplicity, it cannot incorporate the interface wave contribution at subcritical grazing angle for a fast bottom.…”

Section: Statement Of the Problemmentioning

confidence: 99%

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Modeling of monostatic bottom backscattering from three-dimensional volume inhomogeneities and comparisons with experimental data

Li¹

1997

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Acoustic propagation in the ocean inevitably encounters inhomogeneities of various types, which give rise to scattering. Acoustic scattering from rough water /bottom interfaces comprised of exposed rocks and sea mountains gives way to volumetric scattering in areas with fiat interfaces and thick sediment cover. The data analysis of the ARSRP backscattering experiment revealed that random inhomogeneities in two irregular layers beneath the seafloor were the primary contributors to oblique backscattering in a sediment pond on the western flank of the Mid-Atlantic Ridge. In this thesis, an attempt has been made to model monostatic backscattering from 3-D volume inhomogeneities in the sediment and to compare the results with the ARSRP backscattering data.A scattering process cannot be modeled correctly without a proper account of the incident field . Several approximate propagation models have been evaluated against the exact solution, while the appropriateness of using the equivalent surface scattering strength in volume scattering characterizations is studied. This study concludes that precautions need to be taken in modeling both the propagation effects and the scattering mechanisms associated with the bottom volume scattering process.A volume scattering model based on perturbation theory and the Born approximation is developed incorporating contributions from both sound speed and density fluctuations. With the propagation part handled accurately by OASES and random fluctuations generated effectively by a new scheme modified from the spectral method, the model is capable of simulating the monostatic backscattered field and time series due to 3-D volumetric sediment inhomogeneities. Both the characteristic length scale and power spectrum descriptions of the random inhomogeneities are shown to have great impact on the backscattered field by parameter studies in a free-space scenario. The important roles played by horizontal anisotropy and the vertical correlation of the random field have been demonstrated. Density fluctuations are further confirmed to be the dominant force in backscattering. The model matches the ARSRP backscattering data very well , with the fluctuations of sound speed and density in the two irregular layers described by a power law type of power spectrum. To my fellow-students in 5-007 and 5-435, thank you for t he wonderful atmosphere that you have created and t he team-work spirit t hat I have enjoyed. Believe me, you are t he best.Life would not have been so fun without all my friends. Qing, Henry, and Chenyang, how about playing some Tetris the next t ime we get together? And t hank you for introducing me t o the "real world" . Wenjie and Co. , guess no card game is scheduled for now. Thank you, Elaine, for many "Sloanish" advice, Lia ng-wu, for the ride to chase t he sunset, Richard , for the parties, and Feng, for making me a part-time Ashdowner. Helen, Lan and Xiaoou, I will surely not forget t he summer at Cape Cod.My most grateful thanks goes to my parents and my sister. You are ...

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Section: Correlation Functions Of Sound Speed Variationsmentioning

confidence: 99%

Section: Morse and Ingardmentioning

confidence: 99%

Section: Statement Of the Problemmentioning

confidence: 99%

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Modeling of monostatic bottom backscattering from three-dimensional volume inhomogeneities and comparisons with experimental data

Li¹

1997

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“…The work of many researchers has shown that this expression for bottom scattering strength is of the wrong form for small grazing angles for ocean sediments with a sound speed ratio close to or less than one (Holland, 1996). The effect of scattering from the sub-bottom volume of the sediment and from sub-bottom scattering horizons was noted in the results of the CST program and has been included in the modeling work by many researchers over the past 10 years (Mourad, 1993;Yamamoto, 1996;Holland, 1998). ) (Gauss, 2000).…”

Section: Aspm (Acoustic System Performance Model)mentioning

confidence: 99%

Advanced Physics-Based Modeling of Discrete Clutter and Diffuse Reverberation in the Littoral Environment

Neumann¹,

Holland²,

LePage³

2005

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Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. REPORT DATE FEB 20042. REPORT TYPE SPONSOR/MONITOR'S REPORT NUMBER(S) DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release, distribution unlimited SUPPLEMENTARY NOTESThe original document contains color images. ABSTRACTThe results of this Phase I STTR show that a number of the currently identified mechanisms responsible for geoclutter are understood and can be modeled. Charles Holland presents a summary of the observed target-like returns from mud volcanoes. The summary of existing diffuse reverberation models shows the approximations made in currently used models. The research by Kevin LePage presents a capability to directly model broadband time series using a coherent summation of narrowband predictions. This capability applied to both diffuse reverberation and recently to discrete clutter is recommended for continued development and transition into a configuration managed simulation product. Applications of this proposed simulation product have been identified within both the AEER and LAMP program in a meeting with representatives of these programs. At the end of the Phase I base program, the goals of a physics based simulation of a broadband time series including the effects of both discrete clutter and diffuse reverberation for frequencies below 5 KHz are attainable. The proposed Phase I option will allow the development of this simulation package to be continued in the time before the Phase II funding is in place.

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“…The preferential alignments in the Earth ranging from mineral orientations, grain, or micro cracks to regional fractures result in the seismic anisotropy (Crampin, 1994). According to spectral analysis of many cross-well acoustic tomograms and cores collected from seabed locations, the 3-D power spectra of velocity and density fluctuations in the seabed sediments are strongly anisotropic and dipping in general (Yamamoto, 1996). Gurevich (2003) investigated that elastic properties of fluid-saturated porous rocks with aligned fractures can be studied using the model of fractures as linear slip interfaces in an isotropic porous background.…”

Section: Introductionmentioning

confidence: 99%

Reflection and refraction of acoustic waves at poroelastic ocean bed

Vashishth

Sharma

2009

Earth Planet Sp

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Ocean bottom is considered as a plane interface between non-viscous liquid and anisotropic dissipative poroelastic solid. The dissipation comes from the viscosity of pore-fluid as well as the anelasticity of the porous frame. Biot's theory is used to derive a system of modified Christoffel equations for the propagation of plane harmonic waves in a porous medium. The non-trivial solution of this system is ensured by a determinantal equation. This equation is solved into a polynomial equation of degree eight, whose roots represent the vertical slowness values for the waves propagating upward and downward in a porous medium. The eight, numerically obtained, slowness values are identified with the four waves propagating towards (or away from) the boundary in the porous medium. Incidence of acoustic wave through the liquid at the interface results in its reflection and the refraction of four attenuating waves in the poroelastic medium. The energy partition among the reflected and refracted waves is calculated at the interface. Conservation of energy is obtained except in the case of partially opened surface pores of the porous medium. Energy refracted to the dissipative porous medium is expressed through an energy matrix. The four diagonal elements of this matrix represent the energy shares of the four inhomogeneous waves and the sum of all the off-diagonal elements of this matrix represents the interaction energy. Few significant results are extracted from the observations in the numerical examples studied. These results represent the effect of anisotropic symmetries, anelasticity, wave-frequency, opening, configuration and flow-impedance of pores, on the energy shares of reflected and refracted waves.

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Acoustic scattering in the ocean from velocity and density fluctuations in the sediments

Cited by 54 publications

References 17 publications

Modeling of monostatic bottom backscattering from three-dimensional volume inhomogeneities and comparisons with experimental data

Modeling of monostatic bottom backscattering from three-dimensional volume inhomogeneities and comparisons with experimental data

Advanced Physics-Based Modeling of Discrete Clutter and Diffuse Reverberation in the Littoral Environment

Reflection and refraction of acoustic waves at poroelastic ocean bed

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