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High Frequency Bottom Interaction in Range Dependent Biot Media

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LONG TERM GOALS. The long term objective of this project is to understand the dominant physical mechanisms responsible for propagation, attenuation and scattering in low shear velocity, porous sediments such as found on continental margins. Many Navy acoustic systems operate at high frequencies in shallow water over soft, fluid-saturated sedimentary bottoms. In many environments the bottom has range dependent properties such as seafloor roughness or volume heterogeneities within the seafloor. To optimize the performance of these Navy systems it is necessary to fully understand the behavior of acoustic wave propagation and scattering in these complex environments. OBJECTIVES. The finite difference method has proven to be useful in studying acoustic wave propagation in complex media where other methods become invalid. We propose here to extend our Numerical Scattering Chamber, which is based on the finite difference method, to include poro-elastic effects based on Biot theory. With the extended code we will study propagation and scattering effects in real high frequency data from sedimentary environments. Prior work in non-porous media shows that scattering from wavelength size heterogeneities can be responsible for body waves in the sub-bottom that would not be predicted based on Snell s Law Ray Theory using mean medium properties. This phenomenon will cause anomalous sub-bottom penetration and will be relevant for accurately predicting forward and back scatter from realistic environments. We anticipate that similar mechanisms will take place in Biot media and we need to quantify the effect of porosity on the bottom penetration issue. How far below the seafloor do we need to know geophysical parameters in order to accurately predict backscatter in porous environments

Subject Categories:

  • Physical and Dynamic Oceanography
  • Acoustics

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