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Darrell Jackson

Principal Engineer Emeritus

Research Professor Emeritus, Electrical Engineering

Email

drj@apl.washington.edu

Phone

206-543-1359

Biosketch

Darrell Jackson is engaged in theoretical and experimental research in ocean acoustics. This includes random scattering in the ocean, acoustic remote sensing of the ocean bottom, and related signal processing methods.

Department Affiliation

Acoustics

Education

B.S. Electrical Engineering, University of Washington, 1960

M.S. Electrical Engineering, University of Washington, 1963

Ph.D. Electrical Engineering, University of Washington, 1966

Ph.D. Physics, California Institute of Technology, 1977

Publications

2000-present and while at APL-UW

Measurement of sound speed in fine-grained sediments during the Seabed Characterization Experiment

Yang, J., and D.R. Jackson, "Measurement of sound speed in fine-grained sediments during the Seabed Characterization Experiment," IEEE J. Ocean. Eng., EOR, doi:10.1109/JOE.2019.2946004, 2019.

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7 Nov 2019

The Seabed Characterization Experiment was carried out from March 5 to April 10, 2017 (SBCEX17) on the New England Mud Patch, approximately 90 km south of Martha's Vineyard. The SBCEX17 experimental site covers an area of 11 km x 30 km with water depth in the range of 75–80 m. The Sediment Acoustic-speed Measurement System (SAMS) is designed to measure sediment sound speed and attenuation simultaneously over the surficial 3 m of sediments. During SBCEX17, SAMS was successfully deployed at 18 sites, which were chosen to coincide with coring locations, with the goal of developing a geoacoustic model for the study area. In this article, a summary of SAMS operation during SBCEX17 is presented, as well as preliminary results for sediment sound speed and its spatial variation in the frequency band of 2–10 kHz. It is found that in mud, the sound-speed ratio is in the range of 0.98–1. Little dispersion was observed in this frequency band. Using the preliminary SAMS sound-speed results measured at different depths, the sound-speed gradient in mud within the surficial 3 m favors an exponential rather than a linear dependence at SBCEX17 site. Large gradients are observed for depth shallower than 1.5 m. For the sandy basement beneath the mud layer, the sound-speed ratio is as high as 1.105.

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.

A time-domain model for seafloor scattering

Tang, D., and D. Jackson, "A time-domain model for seafloor scattering," J. Acoust. Soc. Am., 142, 2968-2978, doi:10.1121/1.5009932, 2017.

More Info

1 Nov 2017

Bottom scattering is important for a number of underwater applications: it is a source of noise in target detection and a source of information for sediment classification and geoacoustic inversion. While current models can predict the effective interface scattering strength for layered sediments, these models cannot directly compute the ensemble averaged mean-square pressure. A model for bottom scattering due to a point source is introduced which provides a full-wave solution for mean-square scattered pressure as a function of time under first-order perturbation theory. Examples of backscatter time series from various types of seafloors will be shown, and the advantages and limitations of this model will be discussed.

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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