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Kevin Williams

Liaison of SEG & Senior Principal Physicist

Associate Professor, Oceanography

Email

williams@apl.washington.edu

Phone

206-543-3949

Biosketch

Kevin Williams' research efforts include theoretical and experimental examination of scattering from, and propagation within, ocean sediments. He is also involved in research on the effects of ocean internal waves on acoustic imaging.

Dr. Williams has been with the Laboratory since 1988 and now serves as a principal physicist and the Chair of the Ocean Acoustics Department. He holds a Ph.D. in physics (Washington State University) and the post of Associate Professor in the UW School of Oceanography.

Department Affiliation

Acoustics

Education

B.S. Physics, Washington State University, 1979

M.S. Physics, Washington State University, 1983

Ph.D. Physics, Washington State University, 1985

Publications

2000-present and while at APL-UW

Buried targets in layered media: A combined finite element/physical acoustics model and comparison to data on a half buried 2:1 cylinder

Williams, K.L., "Buried targets in layered media: A combined finite element/physical acoustics model and comparison to data on a half buried 2:1 cylinder," J. Acoust. Soc. Am., 140, EL504-EL509, doi:10.1121/1.4971324, 2016.

More Info

1 Dec 2016

Previously, a combined finite element/physical acoustics model for proud targets [K. L. Williams, S. G. Kargl, E. I. Thorsos, D. S. Burnett, J. L. Lopes, M. Zampolli, and P. L. Marston, J. Acoust. Soc. Am. 127, 3356–3371 (2010)] was compared to both higher fidelity finite element models and to experimental data for a proud 2:1 aluminum cylinder. Here that expression is generalized to address the case of a target buried in a layered media. The result is compared to data acquired for the same 2:1 cylinder but half buried in a mud layer that covers the sand sediment (considered here as infinite in extent below the mud layer). The generalized expression reduces to both the previous proud result and to the result for a target buried in an infinite medium under the appropriate limiting conditions. The model/data comparisons shown include both the previous proud model and data results along with the ones for the half buried cylinder. The comparison quantifies the reduction in target strength as a function of frequency in the half buried case relative to the proud case.

Scattering from a finite cylindrical target in a waveguide

Kargl, S.G., T. Shim, K. Williams, and S. Im, "Scattering from a finite cylindrical target in a waveguide," Proc., MTS/IEEE OCEANS Conference, 19-23 September, Monterey, CA, doi:10.1109/OCEANS.2016.7761277 (IEEE, 2016).

More Info

1 Dec 2016

Detection of an object in shallow water has seen a resurgence in importance due to concerns for harbor security. When the horizontal range to an object is large compared to the nominal water depth, then the response of an object to active sonar must necessarily include possible interactions with the boundaries of the waveguide. As an initial step toward the development of detection algorithms, we consider an object in a homogeneous waveguide with planar boundaries. Reflection of the transmitter, receiver, and their images through boundaries allows the scattering problem to be recast into a superposition of many free field scattering problems. An overview of our model and its application to a cylindrical target in littoral waters are given.

Scattering from objects at a water–sediment interface: Experiment, high-speed and high-fidelity models, and physical insight

Kargl, S.G., A.L. España, K.L. Williams, J.L. Kennedy, and J.L. Lopes, "Scattering from objects at a water–sediment interface: Experiment, high-speed and high-fidelity models, and physical insight," IEEE J. Ocean. Eng., 40, 632-642, doi:10.1109/JOE.2014.2356934, 2015.

More Info

1 Jul 2015

In March 2010, a series of measurements were conducted to collect synthetic aperture sonar (SAS) data from objects placed on a water-sediment interface. The processed data were compared to two models that included the scattering of an acoustic field from an object on a water-sediment interface. In one model, finite-element (FE) methods were used to predict the scattered pressure near the outer surface of the target, and then this local target response was propagated via a Helmholtz integral to distant observation points. Due to the computational burden of the FE model and Helmholtz integral, a second model utilizing a fast ray model for propagation was developed to track time-of-flight wave packets, which propagate to and subsequently scatter from an object. Rays were associated with image sources and receivers, which account for interactions with the water-sediment interface. Within the ray model, target scattering is reduced to a convolution of a free-field scattering amplitude and an incident acoustic field at the target location. A simulated or measured scattered free-field pressure from a complicated target can be reduced to a (complex) scattering amplitude, and this amplitude then can be used within the ray model via interpolation. The ray model permits the rapid generation of realistic pings suitable for SAS processing and the analysis of acoustic color templates. Results from FE/Helmholtz calculations and FE/ray model calculations are compared to measurements, where the target is a solid aluminum replica of an inert 100-mm unexploded ordnance (UXO).

More Publications

Acoustics Air-Sea Interaction & Remote Sensing Center for Environmental & Information Systems Center for Industrial & Medical Ultrasound Electronic & Photonic Systems Ocean Engineering Ocean Physics Polar Science Center
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