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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

Scattering from layered seafloors: Comparisons between theory and integral equations

Olson, D.R., and D. Jackson, "Scattering from layered seafloors: Comparisons between theory and integral equations," J. Acoust. Soc. Am., 148, 2086-2095, doi:10.1121/10.0002164, 2020.

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1 Oct 2020

Acoustic scattering from layered seafloors exhibits dependence on both the mean geoacoustic layering, as well as the roughness properties of each layer. Several theoretical treatments of this environment exist, including the small roughness perturbation approximation, the Kirchhoff approximation, and three different versions of the small slope approximation. All of these models give different results for the scattering cross section and coherent reflection coefficient, and there is currently no way to distinguish which model is the most correct. In this work, an integral equation for scattering from a layered seafloor with rough interfaces is presented, and compared with small roughness perturbation method, and two of the small slope approximations. It is found that the most recent small slope approximation by Jackson and Olson [J. Acoust. Soc. Am. 147(1), 56–73 (2020)] is the most accurate when the root-mean-square (rms) roughness is large, and some models are in close agreement with each other when the rms roughness is small.

The small-slope approximation for layered, fluid seafloors

Jackson, D., and D.R. Olson, "The small-slope approximation for layered, fluid seafloors," J. Acoust. Soc. Am., 147, 56-73 doi:10.1121/10.0000470, 2020.

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16 Jan 2020

The small-slope approximation (SSA) for rough-interface scattering is most commonly applied to the upper boundary of either impenetrable media or uniform half-space media, but has been recently developed for layered media in the acoustic and electromagnetic cases. The present work gives an overview of three forms of the SSA for layered media. The first has been previously presented in the acoustics literature. The second is from the electromagnetics literature and in the present work is converted to the fluid-sediment problem. A missing proof is supplied of a key consistency condition demanded of the small-slope ansatz. As is usual, these small-slope results are expressed in k-space. A third SSA for layered seafloors follows from conversion of the usual half-space formulation from k-space to coordinate space. This form turns out to be useful for reverberation simulations. The three different approaches are compared with respect to scattering strength and the coherent reflection coefficient, but an assessment of their relative merits will require comparison with exact calculations.

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., 45, 39-50, doi:10.1109/JOE.2019.2946004, 2020.

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1 Jan 2020

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.

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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