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Terry Ewart

Principal Physicist Emeritus

Professor Emeritus, Oceanography

Email

ewart@apl.washington.edu

Phone

206-543-1327

Research Interests

Medium to small-scale oceanography, wave propagation in random media, stochastic inverse problems between ocean acoustics and oceanography

Department Affiliation

Ocean Physics

Education

B.S. Physics, University of Washington, 1959

Ph.D. Physics, University of Washington, 1965

Publications

2000-present and while at APL-UW

Internal wave effects on high frequency acoustic propagation to horizontal arrays--Experiment and implications to imaging

Williams, K.L., F.S. Henyey, D. Rouseff, S.A. Reynolds, and T.E. Ewart, "Internal wave effects on high frequency acoustic propagation to horizontal arrays--Experiment and implications to imaging," IEEE J. Ocean. Eng., 26, 102-113, 2001.

More Info

1 Jan 2001

An experiment was carried out over a nine day period from August 18 to 27, 1996 to examine acoustic wave propagation in random media at frequencies applicable to synthetic aperture sonar. The objective was to test experimentally the hypothesized imaging effects of variations in the sound speed along two different acoustic paths as put forth by F.S. Henyey et al. (1997). The focus of this paper is on describing the experiment and carrying out an initial analysis of the data in the context of the effect of ocean internal waves on imaging resolution. The oceanography is summarized to the extent needed to discuss important aspects relative to the acoustics experiment. In the acoustics experiment transmissions at 6, 20, 75, and 129 kHz between sources and receiver arrays were carried out. Source to receiver separation was about 815 m. All sources and receivers were mounted on bottom-deployed towers and were at least 9 m off the seafloor. The analysis concentrates on the 75-kHz data acquired during one day of the experiment. The time span examined Is sufficient to examine a diurnal tidal cycle of the oceanographic conditions. The results indicate the IW phase perturbations would have a significant effect on imaging for even the most benign conditions of the experiment if no autofocusing scheme is used. Also, though autofocusing should be useful in recovering the focus for these conditions, there are conditions (e.g., for the path that has a turning point at the thermocline and during times when solibores are present), where more sophisticated compensation schemes would be needed.

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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