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Peter Dahl

Senior Principal Engineer

Professor, Mechanical Engineering





Research Interests

Underwater Acoustics, Acoustic Remote Sensing


Dr. Dahl is a Senior Principal Engineer in the Acoustics Department and a Professor in the University of Washington's Department of Mechanical Engineering. Professor Dahl's research is in areas of acoustics with primary focus on underwater sound. Examples of his research include underwater acoustic remote sensing, the acoustics of underwater explosions, acoustic scattering and reflection from the sea surface and sea bed, vector acoustics, underwater ambient noise and methods to reduce underwater industrial noise.

He has conducted several ocean-going experiments involving underwater acoustics, including the Asian Seas International Acoustics Experiment (ASIAEX), sponsored by the U.S. Office of Naval Research, in the East China Sea involving the U.S., China and Korea and for which he was U.S. chief scientist.

Professor Dahl is a Fellow of the Acoustical Society of America, has served as the chair of its technical committee on underwater acoustics (2002–2005), on its Executive Council (2008–2011), and has recently completed service as Vice President of the Acoustical Society of America.

Department Affiliation



B.S., University of Washington - Seattle, 1976

M.S. Ocean and Fishery Sciences, University of Washington - Seattle, 1982

Ph.D. Ocean Engineering, MIT, 1989


2000-present and while at APL-UW

Coherent reflection recovery in scattering from the ocean surface using the frequency-difference autoproduct

Joslyn, N.J., P.H. Dahl, and D.R. Dowling, "Coherent reflection recovery in scattering from the ocean surface using the frequency-difference autoproduct," J. Acoust. Soc. Am., 155, 1868-1880, doi:10.1121/10.0025234, 2024.

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1 Mar 2024

The coherence of rough sea-surface-scattered acoustic fields decreases with increasing frequency. The frequency-difference autoproduct, a quadratic product of acoustic fields at nearby frequencies, mimics a genuine field at the difference frequency. In rough-surface scattering, the autoproduct's lower effective frequency decreases the apparent surface roughness, restoring coherent reflection. Herein, the recovery of coherent reflection in sea surface scattering via the frequency-difference autoproduct is examined for data collected off the coast of New Jersey during the Shallow Water '06 (SW06) experiment. An acoustic source at depth 40 m and receiver at depth 24.3 m and range 200 m interrogated 160 independent realizations of the ocean surface. The root mean square surface height h was 0.167 m, and broadcast frequencies were 14–20 kHz, so that 2.5 ≤ kh cos θ ≥ 3.7 for acoustic wavenumber k and incidence angle θ⁠. Measured autoproducts, constructed from scattered constituent fields, show significant coherent reflection at sufficiently low difference frequencies. Theoretical results, using the Kirchhoff approximation and a non-analytic surface autocorrelation function, agree with experimental findings. The match is improved using a numerical strategy, exploiting the relationship between autoproduct-based coherence recovery, the ocean-surface autocorrelation function, and the ocean-surface height spectrum. Error bars computed from Monte Carlo scattering simulations support the validity of the measured coherence recovery.

Active intensity vortex and stagnation point singularities in a shallow underwater waveguide

Dahl, P.H., D.R. Dall'Osto, and W.S. Hodgkiss, "Active intensity vortex and stagnation point singularities in a shallow underwater waveguide," J. Acoustic. Soc. Am., 154, 1482-1492, doi:10.1121/10.0020836, 2023.

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11 Sep 2023

Vector acoustic properties of a narrowband acoustic field are observed as a function of range from a source towed in waters of depth 77 m on the New England Mud Patch. At the source frequency (43 Hz), the waveguide supported three trapped modes, with mode 2 weakly excited owing to the towed source depth. The receiving sensor was positioned 1.45 m above the seafloor with a sampling range aperture of 2500 m. The vector acoustics observations enabled study of vortex regions that encompass two singular points for active acoustic intensity: the vortex point, which is co-located with a dislocation, and stagnation point. Interpretative modeling, based on the normal modes and using a geoacoustic model consistent with those emerging from studies conducted at this location, is in agreement with these measurements. Model-data comparisons were based on the first-order variables of acoustic pressure and velocity along with inverse Hankel transforms, which yield normalized horizontal wavenumber spectra, and second-order variables in the form of horizontal and vertical intensity as well as non-dimensional intensity-based ratios. These measures provide a degree of observational confirmation of some vortex region properties. Both observations and modeling point to a gradual deepening of such regions with increasing range owing to sediment attenuation.

Vector acoustic properties of underwater noise from impact pile driving measured within the water column

Dahl, P.H., A. MacGillivray, and R. Racca, "Vector acoustic properties of underwater noise from impact pile driving measured within the water column," Front. Mar. Sci., 10, doi:10.3389/fmars.2023.1146095, 2023.

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29 Mar 2023

Vector acoustic properties of the underwater noise originating from impact pile driving on steel piles has been studied, including the identification of features of Mach wave radiation associated with the radial expansion of the pile upon hammer impact. The data originate from a 2005 study conducted in Puget Sound in the U.S. state of Washington, and were recorded on a four-channel hydrophone system mounted on a tetrahedral frame. The frame system measured the gradient of acoustic pressure in three dimensions (hydrophone separation 0.5 m) from which estimates of kinematic quantities, such as acoustic velocity and acceleration exposure spectral density, were derived. With frame at a depth of 5 m in waters 10 m deep, the data provide an important look at vector acoustic properties from impact pile driving within the water column. Basic features of the Mach wave are observed in both dynamic (pressure) and kinematic measurements, most notably the delay time T leading to spectral peaks separated in frequency by 1/T ~106 Hz, where T equals the travel time of the pile radial deformation over twice the length of the pile. For the two piles studied at range 10 and 16 m, the strike-averaged sound exposure level (SEL) was ~177 dB re 1μPa2
-s and the acceleration exposure level (AEL) was 122–123 dB re μm2/s4 s. The study demonstrates an approximate equivalence of observations based on dynamic and kinematic components of the underwater acoustic field from impact pile driving measured within the water column.

More Publications


Pile with Sound Abatement

Patent Number: 9,617,702

Peter Dahl, John Dardis II, Per Reinhall

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11 Apr 2017

A noise-attenuating pile comprising a pile driving shoe, an outer tube that engages the pile driving shoe, and an inner member that extends through the outer tube and engages the pile driving shoe, wherein the pile is configured to be installed in sediment or other suitable material by driving the inner member with a pile driver, without directly impacting the outer tube, such that the radial outer tube is substantially insulated from the radial expansion waves generated by the pile driver impacting the inner member. In some piles, one of the inner member and the outer tube are removable after installation. In some piles, a seal is provided in a lower end of the channel defined between the inner member and the outer tube, which may be biodegradable, or may be an inflatable bladder, for example.

Pile to Minimize Noise Transmission and Method of Pile Driving

Patent Number: 8,622,658

Per G. Reinhall, Peter Dahl

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7 Jan 2014

A pile and method for driving a pile includes a pile having a structural outer tube, and an inner member disposed generally concentrically with the outer tube. The outer tube and inner member are fixed to a driving shoe. The pile is constructed and driven such that the pile driver impacts only the inner member. The impact loads are transmitted to the driving shoe to drive the pile into the sediment, such that the outer tube is thereby pulled into the sediment. In a particular embodiment the outer tube is formed of steel, and the inner member also comprises a steel tube. In an alternative embodiment one or both of the inner member and the outer tube are formed of an alternative material, for example, concrete. In an embodiment, the outer tube has a recess that captures a flange on the inner member. In an embodiment the outer tube is attached to the inner member with an elastic spring.

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