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Daniel Plotnick

Research Associate

Email

plotnd@apl.uw.edu

Phone

206-543-1328

Department Affiliation

Acoustics

Education

B.S. Physics & Astronomy, Beloit College, 2009

Ph.D. Physics & Astronomy, Washington State University, 2015

Publications

2000-present and while at APL-UW

Circular synthetic aperture sonar imaging of simple objects illuminated by an evanescent wavefield

Plotnick, D.S., T.M. Marston, and P.L. Marston, "Circular synthetic aperture sonar imaging of simple objects illuminated by an evanescent wavefield," J. Acoust. Soc. Am., 140, 2839-2846, doi:10.1121/1.4964329, 2016.

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1 Oct 2016

This paper is motivated by the case where an underwater object located within the sediment is illuminated by a grazing acoustic beam below the critical angle. The included experimental work uses a liquid−liquid interface and vertically inverted geometry as a stand-in for the water−sediment boundary. In the super-critical regime sound in the water column refracts into the sediment before scattering. However, for sub-critical illumination a rapidly decaying evanescent wavefield is generated in the sediment near the water−sediment interface. For compact objects located in the sediment near the interface this can result in strong backscattering signals suitable for acoustic image reconstruction using synthetic aperture sonar techniques. Certain properties of the evanescent wavefield such as the vertical phase-locking behavior, the rapid amplitude decay with distance from the interface, and the low-pass filter effect have understandable ramifications for the image formation process and for characteristics of the reconstructed image. In particular, circular imaging techniques require correct placement of the imaging plane to properly focus an object; however, for backscattering (monostatic) evanescent image formation the imaging plane may be placed at the interface and the target will remain in focus regardless of burial depth. A laboratory experiment using simple scatterers is presented.

High frequency imaging and elastic effects for a solid cylinder with axis oblique relative to a nearby horizontal surface

Plotnick, D.S., and P.L. Marston, "High frequency imaging and elastic effects for a solid cylinder with axis oblique relative to a nearby horizontal surface," J. Acoust. Soc. Am., 140, 1525-1536, doi:10.1121/1.4961001, 2016.

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1 Sep 2016

The calibrated acoustic backscattering spectrum versus aspect angle, also called the "acoustic color" or "acoustic template," of solid cylinders located near a flat interface was previously studied for the case where the cylinder axis was vertically oblique relative to the interface and was insonified by a beam at a non-zero grazing angle. The presence of the interface allows for multiple paths by which sound is backscattered. These multipaths are highly dependent on the relative orientations of the target, the interface, and the source/receiver. In this work, the effects of vertical obliquity on the reconstructed synthetic aperture acoustic images is presented. Several robust orientation dependent features are considered and the physical mechanisms responsible identified through geometric arguments. Information about a target's three-dimensional orientation and size may be gleaned from these images, aiding the interpretation of features within the target's acoustic template. Specific features observed in the reconstructed image are associated with features in the acoustic color. The coupling conditions for surface elastic waves are also considered.

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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