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David Dall'Osto

Senior Research Scientist/Engineer

Email

dallosto@apl.washington.edu

Phone

206-221-5085

Department Affiliation

Acoustics

Education

B.S. Mechanical Engineering, Vanderbilt Univeristy, 2006

M.S. Mechanical Engineering, University of Washington, 2009

Ph. D. Mechanical Engineering, University of Washington, 2013

Publications

2000-present and while at APL-UW

Observations of sea-surface waves during the 2013 Target and Reverberation Experiment (TREX13) and relation to midfrequency sonar

Dahl, P.H., and D.R. Dall'Osto, "Observations of sea-surface waves during the 2013 Target and Reverberation Experiment (TREX13) and relation to midfrequency sonar," IEEE J. Ocean. Eng., EOR, doi:10.1109/JOE.2016.2597718, 2016.

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15 Sep 2016

As part of the 2013 Target and REverberation eXperiment (TREX13), which took place off the coast of Panama City, FL, USA, directional wave measurements were made using two directional wave buoys separated in range by 5 km. The purpose of these measurements was to provide environmental support for the interpretation of reverberation and other active sonar experiments that were part of TREX13. During the measurement period between April 22 and May 17, 2013 exclusive of a period of nondeployment May 2–6, 2013, the root-mean-square (rms) wave height H varied over the range 0.03–0.33 m, holding a median value of 0.11 m; the wind speed varied from ~1 to 10 m/s with a median value of 4.7 m/s, and the rms wave slope averaged over all directions varied from 0.01 to 0.10 with median value of 0.05. These parameters are placed in the context of midfrequency sonar propagation and reverberation prediction. One buoy operated the entire period, with the second buoy operating simultaneously over a four-day overlap period, during which there was excellent agreement between H and wave slope in two orthogonal directions, a finding relevant to describing the sea surface as spatially invariant, or homogeneous, for purposes of sonar modeling. The analysis of energy-weighted mean direction illustrates how the wave field was generally composed of a mixture of swell and wind-generated waves; in cases of purely wind-generated waves the effect of a limited fetch was also shown.

Measurement of acoustic particle motion in shallow water and its application to geoacoustic inversion

Dall'Osto, D.R., C.W. Choi, and P.H. Dahl, "Measurement of acoustic particle motion in shallow water and its application to geoacoustic inversion," J. Acoust. Soc. Am., 139, 311-319, doi:/10.1121/1.4939492, 2016

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15 Jan 2016

Within an underwater acoustic waveguide, the interference among multipath arrivals causes a phase difference in orthogonal components of the particle velocity. When two components of the particle velocity are not in phase, the fluid particles follow an elliptical trajectory. This property of the acoustic field can be readily detected by a vector sensor. A non-dimensional vector quantity, the degree of circularity, is used to quantify how much the trajectory resembles a circle. In this paper, vector sensormeasurements collected during the 2013 Target and Reverberation Experiment are used to demonstrate the effect of multipath interference on the degree of circularity. Finally, geoacoustic properties representing the sandy sediment at the experimental site are inverted by minimization of a cost function, which quantifies the deviation between the measured and modeled degree of circularity.

The underwater sound field from vibratory pile driving

Dahl, P.H., D.R. Dall'Osto, and D.M. Farrell, "The underwater sound field from vibratory pile driving," J. Acoust. Soc. Am., 137, doi:10.1121/1.4921288, 2015.

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1 Jun 2015

Underwater noise from vibratory pile driving was observed using a vertical line array placed at range 16 m from the pile source (water depth 7.5 m), and using single hydrophones at range 417 m on one transect, and range 207 and 436 m on another transect running approximately parallel to a sloping shoreline. The dominant spectral features of the underwater noise are related to the frequency of the vibratory pile driving hammer (typically 15–35 Hz), producing spectral lines at intervals of this frequency. The mean-square pressure versus depth is subsequently studied in third-octave bands. Depth and frequency variations of this quantity observed at the vertical line array are well modeled by a field consisting of an incoherent sum of sources distributed over the water column. Adiabatic mode theory is used to propagate this field to greater ranges and model the observations made along the two depth-varying transects. The effect of shear in the seabed, although small, is also included. Bathymetric refraction on the transect parallel to the shoreline reduced mean-square pressure levels at the 436-m measurement site.

More Publications

Vertical coherence and forward scattering from the sea surface and the relation to the directional wave spectrum

Dahl, P.H., W.J. Plant, and D.R. Dall'Osto, "Vertical coherence and forward scattering from the sea surface and the relation to the directional wave spectrum," J. Acoust. Soc. Am., 134, 1843-1853, doi:10.1121/1.4817846, 2013.

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1 Sep 2013

Results of an experiment to measure vertical spatial coherence from acoustic paths interacting once with the sea surface but at perpendicular azimuth angles are presented. The measurements were part of the Shallow Water 2006 program that took place off the coast of New Jersey in August 2006. An acoustic source, frequency range 6–20 kHz, was deployed at depth 40 m, and signals were recorded on a 1.4-m long vertical line array centered at depth 25 m and positioned at range 200 m. The vertical array consisted of four omni-directional hydrophones and vertical coherences were computed between pairs of these hydrophones. Measurements were made over four source–receiver bearing angles separated by 90°, during which sea surface conditions remained stable and characterized by a root-mean-square wave height of 0.17 m and a mixture of swell and wind waves. Vertical coherences show a statistically significant difference depending on source–receiver bearing when the acoustic frequency is less than about 12 kHz, with results tending to fade at higher frequencies. This paper presents field observations and comparisons of these observations with two modeling approaches, one based on bistatic forward scattering and the other on a rough surface parabolic wave equation utilizing synthetic sea surfaces.

Elliptical acoustic particle motion in underwater waveguides

Dall'Osto, D., and P.H. Dahl, "Elliptical acoustic particle motion in underwater waveguides," J. Acoust. Soc. Am., 134, 109-118, doi:10.1121/1.4807747, 2013.

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1 Jul 2013

Elliptical particle motion, often encountered in acoustic fields containing interference between a source signal and its reflections, can be quantified by the degree of circularity, a vector quantity formulated from acoustic particle velocity, or vector intensity measurements. Acoustic analysis based on the degree of circularity is expected to find application in ocean waveguides as its spatial dependence relates to the acquisition geometry, water column sound speed, surface conditions, and bottom properties. Vector sensor measurements from a laboratory experiment are presented to demonstrate the depth dependence of both the degree of circularity and an approximate formulation based on vertical intensity measurements. The approximation is applied to vertical intensity field measurements made in a 2006 experiment off the New Jersey coast (in waters 80 m deep) to demonstrate the effect of sediment structure on the range dependence of the degree of circularity. The mathematical formulation presented here establishes the framework to readily compute the degree of circularity from experimental measurements; the experimental examples are provided as evidence of the spatial and frequency dependence of this fundamental vector property.

The effect of bottom layering on the acoustic vector field

Dall'Osto, D.R., and P.H. Dahl, "The effect of bottom layering on the acoustic vector field," J. Acoust. Soc. Am., 132, 2092, doi:10.1121/1.4755735, 2012.

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1 Sep 2012

A signal reflected from a layered sea-bed contains information pertaining to the sediment properties. Typically, a signal intended to probe the sea-bed is designed to have a large bandwidth to allow for time separation of arrivals from the multiple layers. Depending on the geometry, it may impossible to avoid interference of these arrivals. The interference of these multiple arrivals does establish a pattern observable in the vector intensity. Measurements of the vertical complex acoustic intensity of a near-bottom source (~λ from the seafloor) collected off the coast of New Jersey in 2006 demonstrate the effect of a sub-bottom layer and the observable interference pattern between the first bottom reflection and the sub-bottom reflection. The spatial structure of the complex intensity can be used to infer bottom properties, which are in close agreement with a number of experimental studies at this location. The observable in the complex intensity can also be directly measured with a particle motion sensor. Parabolic equation simulations of the experimental site are used to demonstrate both the characteristic of the vector field and the sensitivity of these vector properties to changes in the sediment properties.

Underwater vector intensity measurements in the ocean and laboratory

Dall'Osto, D.R., and P.H. Dahl, "Underwater vector intensity measurements in the ocean and laboratory," J. Acoust. Soc. Am., 132, 1985, doi:10.1121/1.4755327, 2012.

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1 Sep 2012

Underwater measurements of the acoustic intensity vector field can be provided by either spatially separated hydrophones or by a sensor measuring a property of particle motion, such as particle acceleration. These measurements are used to formulate the vector intensity as the product of pressure and particle velocity. The magnitude of the vector intensity is not necessarily equal to the plane-wave intensity (the mean square pressure divided by the density and sound-speed of the medium) which is often used to define pressure measurements in terms of intensity. In regions of strong destructive interference, the magnitude of the vector intensity may be greater than the plane-wave intensity. Measurements of an impulsive source on a vertical line array of pressure sensors spanning a shallow sea (60 m) off the coast of South Korea are presented to demonstrate properties of the complex intensity vector field in an ocean waveguide. Here, the vertical complex intensity is formulated by finite-difference methods. These vertical intensity observations in the ocean waveguide have implications on properties of the complete vector field. A laboratory experiment using a tri-axial particle acceleration sensor is presented to provide a connection between measurement of elliptical particle motion and complex intensity.

Waveguide properties of active intensity vorticity

Dall'Osto, D., and P. Dahl, "Waveguide properties of active intensity vorticity," Proceedings, 11th European Conference on Underwater Acoustics, 2-6 July, Edinburgh, 1939-1947 (Institute of Acoustics, 2012).

2 Jul 2012

Properties of the acoustic intensity vector field in a shallow water waveguide

Dall'Osto, D.R., P.H. Dahl, and J.W. Choi, "Properties of the acoustic intensity vector field in a shallow water waveguide," J. Acoust. Soc. Am., 131, 2023-2035, doi:10.1121/1.3682063, 2012.

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1 Mar 2012

Acoustic intensity is a vector quantity described by collocated measurements of acoustic pressure and particle velocity. In an ocean waveguide, the interaction among multipath arrivals of propagating wavefronts manifests unique behavior in the acoustic intensity. The instantaneous intensity, or energy flux, contains two components: a propagating and non-propagating energy flux. The instantaneous intensity is described by the time-dependent complex intensity, where the propagating and non-propagating energy fluxes are modulated by the active and reactive intensity envelopes, respectively.

Properties of complex intensity are observed in data collected on a vertical line array during the transverse acoustic variability experiment (TAVEX) that took place in August of 2008, 17 km northeast of the Ieodo ocean research station in the East China Sea, 63 m depth. Parabolic equation (PE) simulations of the TAVEX waveguide supplement the experimental data set and provide a detailed analysis of the spatial structure of the complex intensity. A normalized intensity quantity, the pressure-intensity index, is used to describe features of the complex intensity which have a functional relationship between range and frequency, related to the waveguide invariant. The waveguide invariant is used to describe the spatial structure of intensity in the TAVEX waveguide using data taken at discrete ranges.

Airborne noise contributions to the underwater noise sound field

Dall'Osto, D.R., and P.H. Dahl, "Airborne noise contributions to the underwater noise sound field," J. Acoust. Soc. Am., 129, 2498, doi:10.1121/1.3588252, 2011.

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1 Apr 2011

Contributions of airborne noise sources to the underwater noise field are the result of two acoustic fields: the transmitted and evanescent. The transmitted field can be represented by only those rays confined to a small cone (about 26 deg) where the reflection coefficient is real-valued. The evanescent field, which arises when rays are totally reflected from the surface, can also contribute to the underwater noise field. Unlike the transmitted field, the evanescent field does not propagate and decays exponentially with depth with a decay rate as a function of frequency. Determining the individual contribution of these two fields to the overall sound field is experimentally difficult to observe. One situation where these two fields can be observed individually occurs when an airplane flies overhead. The Doppler shift associated with tonal propeller noise is dependent on the acoustic path. The frequency separation of the two fields allows for separate analysis of the two fields. Measurements from aircraft (altitude 1000 ft) passing over a buoy equipped with a microphone 3 m above the surface and a hydrophone 2.5 m below the surface will be presented. Numerical simulations are presented along with the experimental observations.

Vertical intensity structure in a shallow water waveguide

Dall'Osto, D.R., P.H. Dahl, and J.W. Choi, "Vertical intensity structure in a shallow water waveguide," J. Acoust. Soc. Am., 129, 2601, doi:10.1121/1.3588624, 2011.

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1 Apr 2011

Acoustic intensity in an ocean waveguide is described by the local pressure and particle velocity, both of which can be described as a sum of modes. Analysis of the interaction between these modal components gives insight into the formation of characteristic intensity structures, such as interference patterns. Observations of the modal structure of the pressure and vertical velocity in a shallow water waveguide are presented using experimental data from an experiment off Korean coastal waters, the transverse acoustic variability experiment (TAVEX) that took place in August of 2008 17 km northeast of the Ieodo weather station, in waters 62 m deep. Mode filtering is performed on a 16 element vertical array that spans the water column (3 m spacing) for broadband (imploding light bulb) sources detonated at ranges from 200 to 1000 m at 40 m depth. The vertical velocity field, determined through the finite-difference approximation, and the pressure field at 230 Hz are represented by six propagating modes and their corresponding modal amplitudes. The interaction of these modal components is analyzed and PE simulated data are presented for comparison. Nondimensional indices are formulated relating the modal components of vector intensity and their utility as field indicators will be discussed.

Implications of signal intensity fluctuations on vector sensor array processing

Dall'Osto, D.R., and P.H. Dahl, "Implications of signal intensity fluctuations on vector sensor array processing," In Proceedings, MTS/IEEE OCEANS 2010, Seattle, 20-23 September, doi:10.1109/OCEANS.2010.5663783 (MTS/IEEE, 2010).

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20 Sep 2010

Vector sensor processing relies on the covariance matrix for both a single vector sensor and a larger matrix from a vector sensor array. The elements of these covariance matrices have physical interpretation in terms of complex intensity. The presence of reactive intensity on the array shows up in the off diagonal elements of the covariance matrix and has significant implications on direction of arrival (DOA) algorithms. Sources of reactive intensity in an underwater waveguide are dependent on the geometry of the system and fluctuations in these quantities affect the ability to increase the array aperture to better resolve arrival angles.

Inventions

Underwater Sound Level Meter

Record of Invention Number: 46351

David Dall'Osto, Per Reinhall, Tim Wen, Peter Dahl

Disclosure

8 Jan 2013

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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