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At the 2003 spring meeting of the Acoustical Society of America, Darin Soukup presented a poster on recent research results on acoustic scattering of low-frequency sound in shallow water environments-an especially challenging environment because of the acoustic interactions with rough sea surfaces, complex water volumes, and variable sediments on the sea bottom. Describing his research with advisor Bob Odom, Darin says, "Through theoretical and numerical work, we attempt to model seismo-acoustic wave propagation in a realistic shallow water environment where anisotropy, gradients, discontinuities, and random heterogeneities may be present."
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Seismic energy in the ocean-undersea earthquakes and volcanism, for example-is converted to acoustic energy that propagates efficiently across entire ocean basins. Several factors, including the rough sea bottom and low-velocity sediment covers, scatter the energy from high- to low-order modes, which have their maximum amplitudes in the SOFAR channel. Heterogeneous anisotropic media such as marine sediments are especially effective scatters. Understanding the propagation of seismo-acoustic waves in shallow water environments then relies on treating the bottom and sub-bottom as elastic solids, and representing the ocean acoustic signal as a superposition of modes. Darin explains, "It is into this framework that we are able to incorporate the effects of rough surface scattering, anisotropy, and volume scattering."
Bob Odom recruited Darin after seeing his graduate application because his background in physics and mathematics at California Polytechnical State University made him a good fit with Odom's research programs. Not long after Darin arrived, Odom asked him to figure out how to run a program that computes the elastic modes of an anisotropic half-space. A colleague at another university wrote the program and published a paper on it, but because the tensor notation in the paper was very compact, Darin derived the results for himself and worked out all the elements of the tensors so he could compare them with the code. He found a number of bugs in the code, and then went on to add a section so that a realistic ocean model could be added to the upper layers. "When I saw the tenacity and careful attention to detail," notes Odom, "I knew I had a truly first-rate graduate student!"
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