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DJ Tang

Senior Principal Oceanographer

Email

djtang@apl.washington.edu

Phone

206-543-1290

Biosketch

Dr. Tang research encompasses ocean bottom interacting acoustics, especially problems involving horizontal, as well as vertical, environmental variabilities; acoustic tomography of sediments; sediment conductivity; wave propagation in range-dependent waveguides; array processing; acoustic scattering by gas bubbles and man-made objects in sediments.

Department Affiliation

Acoustics

Education

B.S. Physics, University of Science and Technology, Hefei, China, 1981

M.S. Physics/Acoustics, Institute of Acoustics, Beijing, China, 1985

Ph.D. Oceanographic Engineering, MIT/WHOI, 1991

Publications

2000-present and while at APL-UW

The mutual scattering cross section

Jackson, D., and D.J. Tang, "The mutual scattering cross section," J. Acoust. Soc. Am., 146, 4611 (2019).

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27 Dec 2019

A generalization of the conventional interface scattering cross section is introduced. This new object will be called the mutual scattering cross section, and, like the conventional cross section, can be used in narrow-band sonar applications. It can treat both sea-surface and seafloor scattering and is useful in cases where large arrays are employed as well as in multipath environments. The application to large arrays with uniform half-space water column and seafloor is examined briefly, but the bulk of this article is devoted to multipathing in the ocean waveguide. Comparisons with more accurate, but more numerically intensive, approaches in range-independent environments show that the mutual cross section can provide an efficient solution for the reverberation intensity time series. The mutual cross section incorporates interference effects causing oscillations in the reverberation time series. Such oscillations have been reported in the literature, but previous modeling efforts have been ad hoc, not based on scattering physics. The mutual cross section is shown to model backscattering enhancement due to multipathing, another phenomenon not seen in simpler models. Expressions for the mutual cross section are derived for seafloor roughness scattering and sediment volume scattering.

Direct-path backscatter measurements along the main reverberation track of TREX13

Tang, D., B.T. Hefner, and D.R. Jackson, "Direct-path backscatter measurements along the main reverberation track of TREX13," IEEE J. Ocean. Eng., 44, 972-983, doi:10.1109/JOE.2019.2901425, 2019.

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20 Mar 2019

The primary goal of the Target and Reverberation Experiment in spring 2013 (TREX13) was to identify the major physical mechanisms responsible for midfrequency reverberation. While both the sea surface and seafloor can contribute to reverberation, the seafloor is typically dominant in shallow water environments. To determine the level of this contribution at the TREX13 site, the bottom backscatter sonar (BBS) was deployed from a dive boat at multiple locations around the site. The BBS consists of a source and a receiver mounted on a short bracket that is suspended above the seafloor to measure direct-path bottom backscatter at 3 kHz. Data near normal incidence were interpreted as bottom reflectivity, which was used to quantitatively explain the range-dependence of the sediment composition at the experiment site. Two factors restricted the estimates of the bottom backscatter strength to the minimum grazing angle of 21°: the currents at the experiment site made it difficult to position the system close to the seafloor, and the shallow water depth resulted in sea surface scatter contaminating small angle bottom backscatter. From the measured backscatter strength and by utilizing available environmental data, initial models of scattering strength indicate that at the shallow grazing angles of importance to reverberation, the scattering on the sand ridges is dominated by roughness scattering while in the muddy areas of the ridge swales, volume scattering dominates. The volume scattering from these mud areas is significantly stronger than the roughness scattering on the ridges by as much as 10 dB and may explain the substantial fluctuations observed in the reverberation as a function of range.

Macroscopic observations of diel fish movements around a shallow water artificial reef using a mid-frequency horizontal-looking sonar

Lee, W.-J., D. Tang, T.K. Stanton, and E.I. Thorsos, "Macroscopic observations of diel fish movements around a shallow water artificial reef using a mid-frequency horizontal-looking sonar," J. Acoust. Soc. Am., 144, 1424-1434, doi:10.1121/1.5054013, 2018.

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18 Sep 2018

The twilight feeding migration of fish around a shallow water artificial reef (a shipwreck) was observed by a horizontal-looking, mid-frequency sonar. The sonar operated at frequencies between 1.8 and 3.6 kHz and consisted of a co-located source and horizontal line array deployed at 4 km from the reef. The experiment was conducted in a well-mixed shallow water waveguide which is conducive to characterizing fish aggregations at these distances. Large aggregations of fish were repeatedly seen to emerge rapidly from the shipwreck at dusk, disperse into the surrounding area during the night, and quickly converge back to the shipwreck at dawn. This is a rare, macroscopic observation of an ecologically-important reef fish behavior, delivered at the level of aggregations, instead of individual fish tracks that have been documented previously. The significance of this observation on sonar performance associated with target detection in the presence of fish clutter is discussed based on analyses of echo intensity and statistics. Building on previous studies of long-range fish echoes, this study further substantiates the unique utility of such sonar systems as an ecosystem monitoring tool, and illustrates the importance of considering the impact of the presence of fish on sonar applications.

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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