APL-UW Home

Jobs
About
Campus Map
Contact
Privacy
Intranet

Todd Hefner

Chair - Acoustics Department & Senior Principal Physicist

Email

hefner@apl.washington.edu

Phone

206-616-7558

Department Affiliation

Acoustics

Education

B.A. Physics, Bard College, 1994

M.S. Physics, Washington State University, 1997

Ph.D. Physics, Washington State University, 2000

Publications

2000-present and while at APL-UW

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.

More Info

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.

More Info

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.

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., 43, 563 - 585, doi:10.1109/JOE.2018.2802578, 2018.

More Info

1 Jul 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.

More Publications

Inventions

Signal Processing and Generating Techniques for an Acoustical Navigation Beacon

Todd Hefner, Benjamin Dzikowicz

Disclosure

15 Jan 2011

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
Close

 

Close