Guest Editorial Special Issue on Sediment Acoustic ... - IEEE Xplore

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in 1965, the M.S. degree from the University of California at Davis-Livermore in engineering and applied science in 1966, and the Ph.D. degree in theoretical ...
IEEE JOURNAL OF OCEANIC ENGINEERING, VOL. 33, NO. 4, OCTOBER 2008

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Guest Editorial Special Issue on Sediment Acoustic Processes

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HIS special issue is devoted to quantifying the effects of sediment properties and seafloor morphology on dispersion, attenuation, reflection, and scattering of acoustic waves, and acoustic detection of buried targets. Papers were solicited on acoustic and environmental measurements and modeling pertaining to scattering from, penetration into, and propagation within shallow-water sediments at frequencies above 100 Hz. Papers on environmental processes, measurements, or modeling need not include acoustic components, but authors of environmental papers were encouraged to discuss the relevance of their papers to acoustic measurements or modeling. Specific topics of interest include the following: 1) measurement and modeling of sediment hydrodynamic, geological, and biological properties and processes that pertain to sediment acoustics (e.g., seabed roughness, sediment heterogeneity, propagation-model parameters, sediment microstructure, bioturbation); 2) monostatic and bistatic scattering (and reflection) from the seafloor; 3) scattering from discrete scatterers (e.g., shells); 4) acoustic penetration into seafloor sediments, especially at subcritical grazing angles; 5) volume scattering and its effects on wave propagation in sediments; 6) modeling of wave propagation in sediments, including the dependence of wave speeds and attenuations on physical properties (e.g., grain size, porosity, and overburden pressure) as well as frequency; and 7) acoustic detection and classification of buried objects. Papers in this special issue will be published in two volumes to speed dissemination of these results. The five papers in this volume are primarily based on high-frequency laboratory experiments. The first two papers analyze measurements of sound-speed dispersion and attenuation in sediments. Sessarego, Ivakin, and Ferrand measured sound propagation (100–1300 kHz) in laboratory sands. At lower frequencies ( 500 kHz), sound speed agrees with predictions from Biot theory with a slight increase in sound speed with frequency. At higher frequencies ( 500 kHz), they observe a decrease in sound speed and greater than linear increase in attenuation with frequency. They attribute the high-frequency behavior to scattering from sand grains. Nosal et al. measured in situ sound speed and attenuation (20–100 kHz) in carbonate sands from Kaneohe Bay, HI. These reef-derived carbonate sands appear indistinguishable from silicate sands with respect to sound speed versus porosity relationships, but exhibit higher attenuation than silicate sands. Frequency-dependent attenuation shows a nearly linear relationship. Best-fit inversions of the Biot poroelastic and Buckingham grain-shearing models are very similar but are unable to match sound-speed dispersion and frequency-dependent attenuation simultaneously. Sessarego, Guillermin, and Ivakin measured normal-incidence acoustic reflection from artificially flattened, water-saturated natural sand and glass beads at high frequencies (200 kHz to 7 MHz) in laboratory experiments. For (acoustic wave

number and particle radius) less than 1, sound reflection follows classic theories using the impedance mismatch between water and sediment. At higher values of , scattering from individual grains contributes to a strong decrease in reflection loss. Baik and Marston develop analytical expressions, based on the Kirchhoff approximation, for backscattering by rigid cylinders breaking through pressure release and rigid surfaces. These expressions are relevant to understanding the backscattering from a partially buried cylinder at the seafloor viewed at grazing incidence. Laboratory experiments for a simpler case, backscattering (120–200 kHz) from a cylinder at the air–water interface, were used to validate one of the analytical expressions. This approach provides an accurate smooth transition in backscattering amplitude as the number of ray paths changes as cylinder exposure in the water was varied between 0% and 100%. Osterhoudt et al. describe laboratory-based measurements (using immiscible liquids of different densities) that are analogous to measurements of evanescent waves at the seafloor. In the unique laboratory configuration used by the authors, the liquid with higher density and slower sound speed representing the water is below the less dense liquid with higher sound speed representing the sediment. In other words, the system is upside down. With the transmitter (40–180 kHz) located at a subcritical angle (total plane wave reflection) to the interface, the sound field in the uppermost liquid was scanned with a hydrophone. The measured sound field, including evanescent waves that decay away from the interface and nulls due to interaction of evanescent and nonevanescent components of the transmitted wave, is very similar to a numerical simulation using OASES (a wave-number-integration-based algorithm). Most papers in the second volume will be devoted to results from the Sediment Acoustics Experiment (SAX04) conducted in August–November 2004 in the northeastern Gulf of Mexico. The results from a similar high-frequency acoustic experiment (SAX99) were published in July 2002, in Volume 27 of the IEEE JOURNAL OF OCEANIC ENGINEERING.

Digital Object Identifier 10.1109/JOE.2008.2011783 0364-9059/$25.00 © 2008 IEEE

ERIC I. THORSOS, Guest Editor Applied Physics Laboratory University of Washington Seattle, WA 98105-6698 USA [email protected] MICHAEL D. RICHARDSON, Associate Editor Marine Geosciences Division Naval Research Laboratory Stennis Space Center, MS 39529-5004 USA [email protected] JAMES F. LYNCH, Special Issues Editor Woods Hole Oceanographic Institution Woods Hole, MA 02543-1541 USA [email protected]

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IEEE JOURNAL OF OCEANIC ENGINEERING, VOL. 33, NO. 4, OCTOBER 2008

Eric I. Thorsos received the B.S. degree in physics from Harvey Mudd College, Claremont, CA, in 1965, the M.S. degree from the University of California at Davis-Livermore in engineering and applied science in 1966, and the Ph.D. degree in theoretical nuclear physics from the Massachusetts Institute of Technology, Cambridge, in 1972. From 1972 to 1975, he was an Assistant Professor of Physics at Hobart and William Smith Colleges, Geneva, NY; from 1975 to 1980, he worked in the area of inertial confinement fusion at the Laboratory for Laser Energetics, University of Rochester, Rochester, NY; and since 1980, he has been at the Applied Physics Laboratory, University of Washington (UW), Seattle. He is currently a Principal Physicist at the Applied Physics Laboratory and an Affiliate Associate Professor in the Electrical Engineering Department, UW. Since 2005, he has been Coordinator for the Office of Naval Research (ONR)-supported basic research projects at the UW related to countering IEDs. His research interests include acoustic scattering from the sea surface and the sea bottom, acoustic propagation in shallow water, and electromagnetic scattering at GHz and THz frequencies. Dr. Thorsos is a Fellow of the Acoustical Society of America and received the Bronze Medal from the National Defense Industrial Association in 1999. He was Chief Scientist for 1999 and 2004 Sediment Acoustics Experiments (SAX99 and SAX04).

Michael D. Richardson received the B.S. degree in oceanography from the University of Washington, Seattle, in 1967, the M.S. degree in marine science from the College of Williams and Mary, Williamsburg, VA, in 1971, and the Ph.D. degree in oceanography from Oregon State University, Corvallis, OR, in 1976. He began working at the Naval Ocean Research and Development Activity, now part of the Naval Research Laboratory (NRL), Stennis Space Center, MS, in 1977. Except for a five-year assignment as Principle Scientist at the NATO Undersea Research Center (NURC), La Spezia, Italy (1995-1989), he has worked at NRL as a Research Scientist and is currently head of the Seafloor Sciences Branch in the Marine Geosciences Division. His research interests include the effects of biological and physical processes on sediment structure, behavior, and physical properties near the sediment–water interface. His current research is linked to high-frequency acoustic scattering from and propagation within the seafloor and prediction of mine burial. Dr. Richardson is a Fellow in the Acoustical Society of America and a member of the American Geophysical Union and Sigma Xi.

James F. Lynch (M’96–SM’02–F’05) was born in Jersey City, NJ, on June 3, 1950. He received the B.S. degree in physics from Stevens Institute of Technology, Hoboken, NJ, in 1972 and the Ph.D. degree in physics from the University of Texas at Austin, in 1978. He then worked for three years at the Applied Research Laboratories, University of Texas at Austin (ARL/UT), from 1978 to 1981, after which he joined the scientific staff at the Woods Hole Oceanographic Institution (WHOI), Woods Hole, MA. He has worked at WHOI since then, and currently holds the position of Senior Scientist and Chairman of the Applied Ocean Physics and Engineering Department. His research specialty areas are ocean acoustics and acoustical oceanography. He also greatly enjoys occasional forays into physical oceanography, marine geology, and marine biology. Dr. Lynch is a Fellow of the Acoustical Society of America and was recently Editor-in-Chief of the IEEE JOURNAL OF OCEANIC ENGINEERING.