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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

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.

More Info

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.

Overview of midfrequency reverberation data acquired during the Target and Reverberation Experiment 2013

Yang, J., D. Tang, B.T. Hefner, K.L. Williams, and J.R Preston, "Overview of midfrequency reverberation data acquired during the Target and Reverberation Experiment 2013," IEEE J. Oceanic Eng., EOR, doi:10.1109/JOE.2018.2802578, 2018.

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16 Mar 2018

The Target and Reverberation EXperiment 2013 (TREX13) included a comprehensive reverberation field project in the frequency band of 2–10 kHz, and was carried out off the coast of Panama City, FL, USA, from April 21 to May 17, 2013. A spatially fixed transmit and receive acoustic system was used to measure reverberation over time under diverse environmental conditions, allowing study of reverberation level (RL) dependence on bottom composition, sea surface conditions, and water column properties. Extensive in situ measurements, including a multibeam bathymetric survey, chirp sonar subbottom profiling, gravity/diver cores, sediment sound speed and attenuation, interface roughness, wind-generated sea surface waves, and water column properties, were made to support studies of environmental effects on RL. Beamformed RL data are categorized to facilitate studies emphasizing physical mechanisms of 1) bottom reverberation; 2) sea surface impact; and 3) biological impact. This paper is an overview of RL over the entire sea trial, intending to summarize major observations and provide both a road map and suitable data sets for follow-up efforts on model/data comparisons. Emphasis is placed on the dependence of RL on local geoacoustic properties and sea surface conditions.

Direct measurements of sediment sound speed and attenuation in the frequency band of 2–8 kHz at the Target and Reverberation Experiment Site

Yang, J., and D. Tang, "Direct measurements of sediment sound speed and attenuation in the frequency band of 2–8 kHz at the Target and Reverberation Experiment Site," IEEE J. Ocean. Eng., 42, 1102-1109, doi:10.1109/JOE.2017.2714722, 2017.

More Info

1 Oct 2017

The sediment acoustic-speed measurement system is designed to measure in situ sediment sound speed and attenuation within the surficial 3 m of sediments in the frequency band of 2–8 kHz. Measurements were carried out during the Target and Reverberation EXperiment 2013 (TREX13) off Panama City, FL, USA. During TREX13, nine deployments at five selected sites were made along the 20-m isobath, termed the main reverberation track. The sediment types at the five selected sites ranged from coarse sand to a mixture of soft mud over sand, and the measured results show a spread of 80 m/s in sediment sound speed among the different types of sediments for all frequencies. Between 2–8 kHz, about 3% dispersion was observed at the sandy sites, whereas little dispersion was observed at the sites with mud. Preliminary attenuation results show 0.5–3.3 dB/m at the sandy sites, and 0.5–1.0 dB/m at the sites with mud in the same frequency band.

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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