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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

Subsurface acoustic ducts in the Northern California current system

Xu, G., R.R. Harcourt, D. Tang, B.T. Hefner, E.I. Thorsos, and J.B. Mickett, "Subsurface acoustic ducts in the Northern California current system," J. Acoust. Soc. Am., 155, 1881-1894, doi:10.1121/10.0024146, 2024.

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7 Mar 2024

This study investigates the subsurface sound channel or acoustic duct that appears seasonally along the U.S. Pacific Northwest coast below the surface mixed layer. The duct has a significant impact on sound propagation at mid-frequencies by trapping sound energy and reducing transmission loss within the channel. A survey of the sound-speed profiles obtained from archived mooring and glider observations reveals that the duct is more prevalent in summer to fall than in winter to spring and offshore of the shelf break than over the shelf. The occurrence of the subsurface duct is typically associated with the presence of a strong halocline and a reduced thermocline or temperature inversion. Furthermore, the duct observed over the shelf slope corresponds to a vertically sheared along-slope velocity profile, characterized by equatorward near-surface flow overlaying poleward subsurface flow. Two potential duct formation mechanisms are examined in this study, which are seasonal surface heat exchange and baroclinic advection of distinct water masses. The former mechanism regulates the formation of a downward-refracting sound-speed gradient that caps the duct near the sea surface, while the latter contributes to the formation of an upward-refracting sound-speed gradient that defines the duct's lower boundary.

Acoustic resonances within the surfical layer of a muddy seabed

Dall'Osto, D.R., and D. Tang, "Acoustic resonances within the surfical layer of a muddy seabed," J. Acoust. Soc. Am., 151, 3473-3480, doi:10.1121/10.0011472, 2022.

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1 May 2022

This is an investigation of sound propagation over a muddy seabed at low grazing angles. Data were collected during the 2017 Seabed and Bottom Characterization Experiment, conducted on the New England Mud Patch, a 500 km2 area of the U.S. Eastern Continental Shelf characterized by a thick layer of muddy sediments. Sound Underwater Signals (SUS), model Mk64, were deployed at ranges of 1–15 km from a hydrophone positioned 1 m above the seafloor. SUS at the closest ranges provide measurements of the bottom reflection at low grazing angles (< 3 deg). Broadband analysis from 10 Hz to 10 kHz reveals resonances in the bottom reflected signals. Comparison of the measurements to simulated signals suggest a surficial layer of mud with a sound speed lower than the underlying mud and overlying water. The low sound speed property at the water–mud interface, which persists for less than 1 m, establishes a sound duct that impacts mid-frequency sound propagation at low grazing angles. The presence of a low-speed surficial layer of mud could be universal to muddy seabeds and, hence, has strong implications for mid-frequency sound propagation wherever mud is present.

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.

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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