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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 University, 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

Vector acoustic analysis of time-separated modal arrivals from explosive sound sources during the 2017 Seabed Characterization Experiment

Dahl, P.H., and D.R. Dall'Osto, "Vector acoustic analysis of time-separated modal arrivals from explosive sound sources during the 2017 Seabed Characterization Experiment," IEEE J. Ocean. Eng., EOR, doi:10.1109/JOE.2019.2902500, 2019.

More Info

26 Mar 2019

The Intensity Vector Autonomous Recorder (IVAR) is a system that records four coherent channels of acoustic data continuously: one channel for acoustic pressure and three channels associated with a triaxial accelerometer from which acoustic particle velocity is obtained. IVAR recorded the vector acoustic field in broadband signals originating from Signal, Underwater Sound (SUS) (Mk-64) charges deployed at 5–13-km range from the fixed IVAR site (mean depth 74.4 m) as part of the 2017 Seabed Characterization Experiment (SBCEX) designed to study the acoustics of fine-grained muddy sediments. Sufficient geometric dispersion at these ranges permitted unambiguous identification of up to four modes as a function of frequency for frequencies less than 80 Hz. From time–frequency analysis of the dispersed arrivals, a single mode (n) and single-frequency (fi) properties are identified at peaks in the narrowband scalar field, with time dependence corresponding to mode group speed. At these time–frequency addresses, four quantities derived from the vector acoustic measurements are formed by coherent combination of pressure and velocity channels: first, modal phase speed; second, circularity, a measure of the normalized curl of active intensity; third, depth-dependent mode speed of energy; and fourth, vertical component of reactive intensity normalized by scalar intensity. A means to compute these quantities theoretically is provided, and a comparison of model results based on a notional geoacoustic representation for the SBCEX experimental area consisting of a single low-speed mud layer over a half-space area versus a Pekeris representation based on the same half-space shows a striking difference, with the field observations also clearly at variance with the Pekeris representation. A fundamental property of mode 2, observed at the IVAR location, is a change in sign for circularity and vertical reactive intensity near 37 Hz that is posited as a constraint observation for mode 2 that must be exhibited by any geoacoustic model that includes a low-speed mudlike layer applied to this location.

Observations of water column and bathymetric effects on the incident acoustic field associated with shallow-water reverberation experiments

Dall'Osto, D.R., and P.H. Dahl, "Observations of water column and bathymetric effects on the incident acoustic field associated with shallow-water reverberation experiments," IEEE J. Ocean. Eng., 42, 1146-1161, doi:10.1109/JOE.2017.2717661, 2017.

More Info

1 Oct 2017

As a part of the 2013 Targets and Reverberation Experiment (TREX13), measurements of the acoustic field generated by a source used in midfrequency (1.8–3.6 kHz) reverberation experiments are studied at 5 and 6 km range. The TREX13 reverberation sources were placed off the coast of Panama City, FL, USA, in waters ~20 m deep, and data discussed here are from a 2-h period in the late afternoon on April 28, 2013. The observed coda of the source signal is partitioned into an initial primary arrival, and a distinct second arrival delayed by roughly 2 s. Characteristics of the two arrivals are studied in terms of the effective number of modes, interference features, and the direction of acoustic intensity, which was directly measured by a vector sensor located at 5 km range. A shift in frequency within the primary arrival is observed over the 2-h measurement period. Frequency shifts are related to a change in range of dislocations, defined as points of complete destructive interference in the acoustic field, that modulate with tidal variation in the sound-speed profile. Precise frequencies are identified with the vector property called circularity, a nondimensional measure of acoustic intensity curl, that is maximal within the vortex-like intensity field within a dislocation. Using the waveguide invariant β, the frequency shift is used to estimate the tidal change in the thermocline depth. These interference features are absent in the second arrival, which is postulated to be an acoustic path horizontally refracted by the gently sloping bathymetry (~0.4°) forming the coastal environment. A description of the refraction using modal rays is developed, and the transition of the mode from being trapped to leaky is handled as a transition to a virtual mode near the cutoff depth. Models of the primary and refracted arrivals are presented to support the conclusions.

On the underwater sound field from impact pile driving: Arrival structure, precursor arrivals, and energy streamlines

Dahl, P.H., and D.R. Dall'Osto, "On the underwater sound field from impact pile driving: Arrival structure, precursor arrivals, and energy streamlines," J. Acoust. Soc. Am., 142, 1141, doi:10.1121/1.4999060, 2017.

More Info

1 Aug 2017

Underwater noise from impact pile driving is studied through measurements using a vertical line array (VLA) placed at range 120 m from the pile source (water depth 7.5 m) over which bathymetry varied gradually increasing to depth 12.5 m at the VLA. The data were modeled assuming the pile impact produces a radial expansion that acts as sound source and propagates along the pile at supersonic speed. This leads to the conceptualization of the pile as a discrete, vertical line source for which frequency- and source-depth-dependent complex phasing is applied. Dominant features of the pressure time series versus measurement depth are reproduced in modeled counterparts that are linearly related. These observations include precursor arrivals for which arrival timing depends on hydrophone depth and influence of a sediment sound speed gradient on precursor amplitude. Spatial gradients of model results are taken to obtain estimates of acoustic particle velocity and vector intensity for which active intensity is studied in the time domain. Evaluation of energy streamlines based on time-integrated active intensity, and energy path lines based on instantaneous (or very-short-time integrated) active intensity reveal interesting structure in the acoustic field, including an inference as to the source depth of the precursor.

More Publications

Inventions

Automatic Implementation of NOAA Marine Mammal Guidelines

Record of Invention Number: 48478

Peter Dahl, David Dall'Osto

Disclosure

13 Nov 2018

Airborne Acoustic Particle Motion Sound Meter

Record of Invention Number: 48135

David Dall'Osto, Peter Dahl

Disclosure

1 Aug 2017

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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