Low-frequency acoustic backscattering by volumetric inhomogeneities in deep-ocean sediments

Tang, Dajun; Frisk, George V.; Sellers, Cynthia J.; Li, Dan

doi:10.1121/1.413641

Cited by 11 publications

(8 citation statements)

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“…As part of the Acoustic Reverberation Special Research Program (A RSRP), low-frequency bottom scattering from a deep ocean sediment pond was measured using an omnidirectional source and a vertical line receiving array deployed near the bottom. Sediment volume heterogeneities in two irregular layers beneath the water/sediment interface were found to be the major contributors to the measured scattered fields [1]. In this work, efforts have been made to model backscattering from 3-D sediment volume heterogeneities and to compare the results with the ARSRP backscattering data.…”

Section: Introductionmentioning

confidence: 99%

Bottom volume scattering—Modeling and data analysis

Frisk

Tang

1998

The Journal of the Acoustical Society of America

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Section: Introductionmentioning

confidence: 99%

Bottom volume scattering—Modeling and data analysis

Frisk

Tang

1998

The Journal of the Acoustical Society of America

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“…The model is expected to interpret the phenomena which have been observed in the ARSRP site A sediment scattering experiment [9,10].…”

Section: Objective and Approachmentioning

confidence: 99%

“…So we see from the above that the single stationary point treatment in the far-field approximation works better in a high-attenuation bottom than in a low-attenuation one. Both in the ARSRP low-frequency sediment scattering experiment and the CBBL high-frequency scattering experiment at the Eckernfoerde Bay site, strong scattering layers are found to be a certain distance away from the water j sediment interface [9,6]. So we will choose a scattering layer with a thickness of 50>.…”

Section: ~-40mentioning

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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“…The scattering is influenced by the roughness of the interfaces between the water and bottom and subbottom layers as well as inhomogeneities ͑Medwin and Clay, 1998; Ogilvy, 1991;Urick, 1983;Jackson et al, 1986a, b;Jackson and Briggs, 1992;Jackson and Ivakin, 1998;Stanic et al, 1989;Tang et al, 1994Tang et al, , 1995Richardson and Briggs, 1996; There are both continuously varying inhomogeneities and discrete ones. Rocks, shells, and gas pockets are among the discrete inhomogeneities.…”

Section: Introductionmentioning

confidence: 99%

On acoustic scattering by a shell-covered seafloor

Stanton

2000

The Journal of the Acoustical Society of America

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Acoustic scattering by the seafloor is sometimes influenced, if not dominated, by the presence of discrete volumetric objects such as shells. A series of measurements of target strength of a type of benthic shelled animal and associated scattering modeling have recently been completed ͑Stanton et al., ''Acoustic scattering by benthic and planktonic shelled animals,'' J. Acoust. Soc. Am., this issue͒. The results of that study are used herein to estimate the scattering by the seafloor with a covering of shells at high acoustic frequencies. A simple formulation is derived that expresses the area scattering strength of the seafloor in terms of the average reduced target strength or material properties of the discrete scatterers and their packing factor ͑where the reduced target strength is the target strength normalized by the geometric cross section of the scatterers and the averaging is done over orientation and/or a narrow range of size or frequency͒. The formula shows that, to first order, the backscattering at high acoustic frequencies by a layer of shells ͑or other discrete bodies such as rocks͒ depends principally upon material properties of the objects and packing factor and is independent of size and acoustic frequency. Estimates of area scattering strength using this formula and measured values of the target strength of shelled bodies from Stanton et al. ͑this issue͒ are close to or consistent with observed area scattering strengths due to shell-covered seafloors published in other papers.

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Low-frequency acoustic backscattering by volumetric inhomogeneities in deep-ocean sediments

Cited by 11 publications

References 0 publications

Bottom volume scattering—Modeling and data analysis

Bottom volume scattering—Modeling and data analysis

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

On acoustic scattering by a shell-covered seafloor

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