Scattering of acoustic energy from rough deep ocean seafloor: A numerical modeling approach

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dc.contributor.advisorLevander, Alan R.en_US
dc.creatorRobertsson, Johan Olof Andersen_US
dc.date.accessioned2009-06-04T00:11:35Zen_US
dc.date.available2009-06-04T00:11:35Zen_US
dc.date.issued1995en_US
dc.description.abstractThe highly heterogeneous and anelastic nature of deep ocean seafloor results in complex reverberation as acoustic energy incident from the overlaying water column interacts and scatters from it. To gain a deeper understanding of the mechanisms causing the reverberation in sonar and seafloor scattering experiments, we have developed numerical simulation techniques that are capable of modeling the principal physical properties of complex seafloor structures. A new viscoelastic finite-difference technique for modeling anelastic wave propagation in 2-D and 3-D heterogeneous media, as well as a computationally optimally efficient method for quantifying the anelastic properties in terms of viscoelastic mechanics are presented. A method for reducing numerical dispersion using a Galerkin-wavelet formulation that enables large computational savings is also presented. The widely different regimes of wave propagation occurring in ocean acoustic problems motivate the use of hybrid simulation techniques. HARVEST (Hybrid Adaptive Regime Visco-Elastic Simulation Technique) combines solutions from Gaussian beams, viscoelastic finite-differences, and Kirchhoff extrapolation, to simulate large offset scattering problems. Several scattering hypotheses based on finite-difference simulations of short-range acoustic scattering from realistic seafloor models are presented. Anelastic sediments on the seafloor are found to have a significant impact on the backscattered field from low grazing angle scattering experiments. In addition, small perturbations in the sediment compressional velocity can also dramatically alter the backscattered field due to transitions between pre- and post-critical reflection regimes. The hybrid techniques are employed to simulate deep ocean acoustic reverberation data collected in the vicinity of the northern mid-Atlantic ridge. In general, the simulated data compare well to the real data. Noise partly due to side-lobes in the beam-pattern of the receiver-array is the principal source of reverberation at lower levels. Overall, the employed seafloor models were found to model the real seafloor well. Inaccurately predicted events may partly be attributed to the intrinsic uncertainty in the stochastic seafloor models. For optimal comparison between real and HARVEST simulated data the experimental geometry should be chosen so that 3-D effects may be ignored, and to yield a cross-range resolution in the beam-formed acoustic data that is small relative to the lineation of the seafloor.en_US
dc.format.extent322 p.en_US
dc.format.mimetypeapplication/pdfen_US
dc.identifier.callnoTHESIS GEOL. 1995 ROBERTSSONen_US
dc.identifier.citationRobertsson, Johan Olof Anders. "Scattering of acoustic energy from rough deep ocean seafloor: A numerical modeling approach." (1995) Diss., Rice University. <a href="https://hdl.handle.net/1911/16873">https://hdl.handle.net/1911/16873</a>.en_US
dc.identifier.urihttps://hdl.handle.net/1911/16873en_US
dc.language.isoengen_US
dc.rightsCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.subjectGeophysicsen_US
dc.subjectAcousticsen_US
dc.subjectOcean engineeringen_US
dc.titleScattering of acoustic energy from rough deep ocean seafloor: A numerical modeling approachen_US
dc.typeThesisen_US
dc.type.materialTexten_US
thesis.degree.departmentEarth Scienceen_US
thesis.degree.disciplineNatural Sciencesen_US
thesis.degree.grantorRice Universityen_US
thesis.degree.levelDoctoralen_US
thesis.degree.nameDoctor of Philosophyen_US
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