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Todd Hefner

Chair - Acoustics Department & Senior Principal Physicist





Department Affiliation



B.A. Physics, Bard College, 1994

M.S. Physics, Washington State University, 1997

Ph.D. Physics, Washington State University, 2000


2000-present and while at APL-UW

Observed correlations between the sediment grain size and the high-frequency backscattering strength

Wendelboe, G., T. Hefner, and A. Ivakin, "Observed correlations between the sediment grain size and the high-frequency backscattering strength," JASA Express Lett., 3, doi:10.1121/10.0017107, 2023.

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1 Feb 2023

In March 2019, Teledyne RESON and the Applied Physics Laboratory at the University of Washington conducted surveys with a calibrated multibeam echosounder at ten sites in Sequim Bay, a shallow sheltered bay in Washington State, USA. For each site, the mean grain size was obtained from a diver core sample, and estimates of the backscattering strength at frequencies ranging between 200 and 350 kHz were calculated. The correlation between the backscattering strength and the normalized grain size have been investigated for the grazing angles 45° and 75°. For 45°°, a correlation consistent with previous results has been found. It demonstrates the potential for simple seabed classification.

Reverberation due to a moving, narrowband source in an ocean waveguide

Hefner, B.T., and W.S. Hodgkiss, "Reverberation due to a moving, narrowband source in an ocean waveguide," J. Acoust. Soc. Am., 146, 1661-1670, doi:10.1121/1.5126023, 2019.

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1 Sep 2019

In this paper, a model for the bistatic reverberation associated with seafloor scattering of sound from a moving, narrowband source in an ocean waveguide is developed. Studies of the Doppler effect for moving sources in waveguides have typically focused on the forward propagating field where the Doppler shift leads to a splitting or broadening of the received spectrum. In contrast, the contributions to the scattered field come from all directions and as a consequence the spectrum of the received energy is spread across the entire range of Doppler-shifted frequencies possible for the speed of the source. The model developed here uses rays for the incident field, ray-mode analogies for the scattering, and normal modes to propagate the scattered field to the receiver. Results from this model are compared with data collected using a towed source during the Target and Reverberation Experiment 2013. The possible applications of this Doppler reverberation for seafloor characterization are also considered.

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.

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