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Frank Henyey

Senior Principal Physicist

Email

frank@apl.washington.edu

Phone

206-543-4856

Research Interests

Ocean Acoustics, Small Scale Physical Oceanography

Department Affiliation

Acoustics

Education

B.A. Physics, University of California, Berkeley, 1963

Ph.D. Physics, California Institute of Technology, 1967

Publications

2000-present and while at APL-UW

Large-amplitude internal solitary waves observed in the northern South China Sea: Properties and energetics

Lien, R.-C., F. Henyey, B. Ma, and Y.J. Yang, "Large-amplitude internal solitary waves observed in the northern South China Sea: Properties and energetics," J. Phys. Oceanogr., 44, 1095-1115, doi:10.1175/JPO-D-13-088.1, 2014.

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1 Apr 2014

Five large-amplitude internal solitary waves (ISWs) propagating westward on the upper continental slope in the northern South China Sea were observed in May–June 2011 with nearly full-depth measurements of velocity, temperature, salinity, and density. As they shoaled, at least three waves reached the convective breaking limit: along-wave current velocity exceeded the wave propagation speed C. Vertical overturns of ~100 m were observed within the wave cores; estimated turbulent kinetic energy was up to 1.5 x 10-4 W kg-1. In the cores and at the pycnocline, the gradient Richardson number was mostly <0.25. The maximum ISW vertical displacement was 173 m, 38% of the water depth. The normalized maximum vertical displacement was ~0.4 for three convective breaking ISWs, in agreement with laboratory results for shoaling ISWs. Observed ISWs had greater available potential energy (APE) than kinetic energy (KE). For one of the largest observed ISWs, the total wave energy per unit meter along the wave crest E was 553 MJ m-1, more than three orders of magnitude greater than that observed on the Oregon Shelf. Pressure work contributed 77% and advection contributed 23% of the energy flux. The energy flux nearly equaled CE. The Dubriel–Jacotin–Long model with and without a background shear predicts neither the observed APE > KE nor the subsurface maximum of the along-wave velocity for shoaling ISWs, but does simulate the total energy and the wave shape. Including the background shear in the model results in the formation of a surface trapped core.

A Method to Determine Small-Scale Internal Wave and Spice Fields from a Single CTD Profile with Application to Three Long-Range Ocean Acoustics Experiments

Henyey, F.S., J.A. Mercer, R.K. Andrew, and A.W. White, "A Method to Determine Small-Scale Internal Wave and Spice Fields from a Single CTD Profile with Application to Three Long-Range Ocean Acoustics Experiments," Technical Memorandum, APL-UW TM 1-14, Applied Physics Laboratory, University of Washington, Seattle, 59 pp.

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20 Mar 2014

The smaller vertical scales of sound speed variability of several recent deep water Pacific
Ocean acoustic experiments are extracted from individual conductivity, temperature, depth
(CTD) casts taken along the acoustic paths of these experiments, close to the times of
the experiments. The sound speed variability is split into internal wave variability and
spice variability, as these two parts obey very different dynamics %u2013 the internal waves move
through the water and the spice field moves with the water. Larger scales are mostly
responsible for acoustic travel time fluctuations, but smaller scales are mostly responsible
for other important phenomena such as intensity and arrival angle fluctuations. A method
is presented to determine when the two components are separable. The internal wave
properties are consistent with a spectral model such as a generalized Garrett%u2013Munk model,
whereas the spice is very intermittent, and the measurements are not extensive enough
to confidently make a spice model for acoustic propagation purposes. Both the internal
wave results and the spice results are summarized as vertical wavenumber spectra over a
selected vertical depth interval, but with the spice, it must be understood that a spectral
model would be very different from the data, and that the three-dimensional horizontal%u2013
vertical spectrum would be pure conjecture. The spectral level of the (small-scale) spice,
averaged over all the profiles, is comparable to that of the internal waves, suggesting that it
is not significantly less important to acoustic propagation than are the (small-scale) internal
waves.

Reverberation clutter induced by nonlinear internal waves in shallow water

Henyey, F.S., and D. Tang, "Reverberation clutter induced by nonlinear internal waves in shallow water," J. Acoust. Soc. Am., 134, EL289, doi:10.1121/1.4818937, 2013.

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1 Oct 2013

Clutter is related to false alarms for active sonar. It is demonstrated that, in shallow water, target-like clutter in reverberation signals can be caused by nonlinear internal waves. A nonlinear internal wave is modeled using measured stratification on the New Jersey shelf. Reverberation in the presence of the internal wave is modeled numerically. Calculations show that acoustic energy propagating near a sound speed minimum is deflected as a high intensity, higher angle beam into the bottom, where it is backscattered along the reciprocal path. The interaction of sound with the internal wave is isolated in space, hence resulting in a target-like clutter, which is found to be greater than 10 dB above the mean reverberation level.

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Comparison of transport theory predictions with measurements of the decrease in shallow water reverberation level as the sea state increases

Thorsos, E., J. Yang, W.T. Elam, F.S. Henyey, F. Li, and J. Liu, "Comparison of transport theory predictions with measurements of the decrease in shallow water reverberation level as the sea state increases," Proc., Meetings on Acoustics, 19, 070024, doi:10.1121/1.4800711, 2013.

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2 Jun 2013

Transport theory has been developed for modeling shallow water propagation and reverberation at mid frequencies (1-10 kHz) where forward scattering from a rough sea surface is taken into account in a computationally efficient manner. The method is based on a decomposition of the field in terms of unperturbed modes, and forward scattering at the sea surface leads to mode coupling that is treated with perturbation theory. Reverberation measurements made during ASIAEX in 2001 provide a useful test of transport theory predictions. Modeling indicates that the measured reverberation was dominated by bottom reverberation, and the reverberation level at 1 and 2 kHz was observed to decrease as the sea surface conditions increased from a low sea state to a higher sea state. This suggests that surface forward scattering was responsible for the change in reverberation level. By modeling the difference in reverberation as the sea state changes, the sensitivity to environmental conditions other than the sea surface roughness is much reduced. Transport theory predictions for the reverberation difference are found to be in good agreement with measurements.

Reverberation modeling with transport theory

Thorsos, E.I., J. Yang, W.T. Elam, and F.S. Henyey, "Reverberation modeling with transport theory," J. Acoust. Soc. Am., 131, 3355, doi:10.1121/1.4708579, 2012.

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1 Apr 2012

Transport theory has been developed for modeling shallow water propagation at mid frequencies (1-10 kHz) where forward scattering from a rough sea surface is taken into account in a computationally efficient manner. The method is based on a decomposition of the field in terms of unperturbed modes, and forward scattering at the sea surface leads to mode coupling that is treated with perturbation theory. Transport theory has recently been extended to model shallow water reverberation, including the effect of forward scattering from the sea surface. Transport theory results will be compared with other solutions for reverberation examples taken from ONR Reverberation Modeling Workshop problems. These comparisons show the importance of properly accounting for multiple forward scattering in shallow water reverberation modeling.

The 2009 Philippine Sea pilot study/engineering test and the 2010 Philippine Sea experiment: University of Washington cruises

Mercer, J., R. Andrew, L. Buck, G. D'Spain, M. Dzieciuch, A. Ganse, F. Henyey, A. White, and P. Worcester, "The 2009 Philippine Sea pilot study/engineering test and the 2010 Philippine Sea experiment: University of Washington cruises," J. Acoust. Soc. Am., 131, 3352, doi:10.1121/1.,4708563 2012.

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1 Apr 2012

Investigators at the University of Washington's Applied Physics Laboratory collaborated with scientists from the Scripps Institution of Oceanography during the 2009 Philippine Sea Pilot Study/Engineering Test and the 2010 Philippine Sea Experiment. The focus of both efforts was to collect well controlled low-frequency acoustic propagation data and detailed environmental information. The data from these cruises are presently being analyzed in the interests of: horizontal statistics of ocean spice as measured on a towed conductivity-temperature-depth (pressure) chain, fluctuation measures of low-frequency broadband ocean acoustic signals, bottom properties, and associated theoretical developments. This presentation will outline the experimental plans for each year, discuss preliminary analysis results, and provide an introduction for more detailed presentations in the remainder of this session.

Trapped core formation within a shoaling nonlinear internal wave

Lien, R.-C., E.A. D'Asaro, F. Henyey, M.-H. Chang, T.-T. Tang, and Y.-J. Yang, "Trapped core formation within a shoaling nonlinear internal wave," J. Phys. Oceanogr., 42, 511-525, doi:10.1175/2011JPO4578.1, 2012.

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1 Apr 2012

Large-amplitude (100–200 m) nonlinear internal waves (NLIWs) were observed on the continental slope in the northern South China Sea nearly diurnally during the spring tide. The evolution of one NLIW as it propagated up the continental slope is described. The NLIW arrived at the slope as a nearly steady-state solitary depression wave. As it propagated up the slope, the wave propagation speed C decreased dramatically from 2 to 1.3 m s-1, while the maximum along-wave current speed Umax remained constant at 2 m s-1. As Umax exceeded C, the NLIW reached its breaking limit and formed a subsurface trapped core with closed streamlines in the coordinate frame of the propagating wave. The trapped core consisted of two counter-rotating vortices feeding a jet within the core. It was highly turbulent with 10–50-m density overturnings caused by the vortices acting on the background stratification, with an estimated turbulent kinetic energy dissipation rate of O(10-4) W kg-1 and an eddy diffusivity of O(10-1) m2 s-1. The core mixed continually with the surrounding water and created a wake of mixed water, observed as an isopycnal salinity anomaly. As the trapped core formed, the NLIW became unsteady and dissipative and broke into a large primary wave and a smaller wave. Although shoaling alone can lead to wave fission, the authors hypothesize that the wave breaking and the trapped core evolution may further trigger the fission process. These processes of wave fission and dissipation continued so that the NLIW evolved from a single deep-water solitary wave as it approached the continental slope into a train of smaller waves on the Dongsha Plateau. Observed properties, including wave width, amplitude, and propagation speed, are reasonably predicted by a fully nonlinear steady-state internal wave model, with better agreement in the deeper water. The agreement of observed and modeled propagation speed is improved when a reasonable vertical profile of background current is included in the model.

Transport theory for shallow water propagation with rough boundaries

Thorsos, E.I., F.S. Henyey, W.T. Elam, B.T. Hefner, S.A. Reynolds, and J. Yang, "Transport theory for shallow water propagation with rough boundaries," In Proceedings, Second International Shallow-Water Acoustics Conference (SWAC'09), Shanghai, 16-20 September 2009, 99-105 (AIP, 2010).

4 Oct 2010

Transport theory for shallow water propagation with rough boundaries

Thorsos, E.I., F.S. Henyey, W.T. Elam, B.T. Hefner, S.A. Reynolds, and J. Yang, "Transport theory for shallow water propagation with rough boundaries," In Proceedings, Second International Shallow-Water Acoustics Conference, Shanghai, 16-20 September 2009, 99-105 (AIP, 2010).

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6 Sep 2010

At frequencies of about 1 kHz and higher, forward scattering from a rough sea surface (and/or a rough bottom) can strongly affect shallow water propagation and reverberation. The need exists for a fast, yet accurate method for modeling such propagation where multiple forward scattering occurs. A transport theory method based on mode coupling is described that yields the first and second moments of the field. This approach shows promise for accurately treating multiple forward scattering in one-way propagation. The method is presently formulated in two space dimensions, and Monte–Carlo rough surface PE simulations are used for assessing the accuracy of transport theory results.

Simultaneous nearby measurements of acoustic propagation and high-resolution sound-speed structure containing internal waves

Henyey, F.S., K.L. Williams, J. Yang, and D. Tang, "Simultaneous nearby measurements of acoustic propagation and high-resolution sound-speed structure containing internal waves," IEEE J. Ocean. Eng., 35, 684-694, doi:10.1109/JOE.2010.2044671, 2010.

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26 Aug 2010

During the 2006 Shallow Water (SW06) experiment, simultaneous measurements were made of the sound-speed field as a function of range and depth associated with nonlinear internal waves and acoustic propagation at frequencies of 2–10 kHz over a 1-km path. The internal waves were measured by a towed conductivity-temperature-depth (CTD) chain to get high resolution. These measurements were coordinated so that the nonlinear waves could be interpolated onto the acoustic path, allowing predictions of their effects on the acoustics. Using the measured sound-speed field, the acoustic arrivals under the influence of the internal waves are modeled and compared to data. The largest impact of measured moderate amplitude internal waves on acoustics is that they alter the arrival time of the rays which turn at the thermocline.

Effect of the internal tide on acoustic transmission loss at midfrequencies

Yang, J., D. Rouseff, D. Tang, and F.S. Henyey, "Effect of the internal tide on acoustic transmission loss at midfrequencies," IEEE J. Ocean. Eng., 35, 3-11, doi:10.1109/JOE.2009.2038984, 2010.

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2 Feb 2010

Nonlinear internal waves are a common event on the continental shelf. The waves depress the high-gradient region of the thermocline and thicken the surface mixed layer with consequent effect on acoustic propagation. After the waves have passed, it may take several hours for the thermocline to rise to its prewave level.

To examine the effect of the rising thermocline, oceanographic and acoustic data collected during the 2006 Shallow Water Experiment (SW06) are analyzed. Midfrequency acoustic data (1.5-10.5 kHz) taken for several hours at both fixed range (550 m) and along a tow track (0.1-8.1 km) are studied. At the fixed range, the rising thermocline is shown to increase acoustic intensity by approximately 5 dB. Along the tow track, the transmission loss changes 2 dB for a source-receiver pair that straddles the thermocline. Using oceanographic moorings up to 2.2 km away from the acoustic receiver, a model for the rising thermocline is developed. This ocean model is used as input to a broadband acoustic model. Results from the combined model are shown to be in good agreement with experimental observation. The effects on acoustic signals are shown to be observable, significant, and predictable.

Simulating realistic-looking sediment ripple fields

Tang, D., F.S. Henyey, B.T. Hefner, and P.A Traykovski, "Simulating realistic-looking sediment ripple fields," IEEE J. Ocean. Eng., 34, 444-450, doi:10.1109/JOE.2009.2025905, 2009.

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30 Oct 2009

Sandy sediment ripples impact sonar performance in coastal waters through Bragg scattering. Observations from data suggest that sandy ripple elevation relative to the mean seafloor as a function of the horizontal coordinates is not Gaussian distributed; specifically, peak amplitude fading over space associated with a random Gaussian process is largely absent. Such a non-Gaussian nature has implications for modeling acoustic scattering from, and penetration into, sediments. An algorithm is developed to generate ripple fields with a given power spectrum; these fields have non-Gaussian statistics and are visually consistent with data. Higher order statistics of these ripple fields and their implications to sonar detection are discussed.

Center for the studies of nonlinear dynamics, 1982-1985

Henyey, F.S., "Center for the studies of nonlinear dynamics, 1982-1985," J. Acoust. Soc. Am., 126, 2157, doi:10.1121/1.3248384, 2009.

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1 Oct 2009

Stan Flatte was the third director of the Center for the Studies of Nonlinear Dynamics (CSND), from 1982 to 1985 (and for another year after he returned to Santa Cruz). Upon joining CSND, he assembled a group to work on the path integral method for predicting internal wave effects on acoustic propagation in the ocean. This talk discusses the work done by that group. Topics of this work include travel time bias, relation to moment equation methods, fourth moment calculations, and pulse spread.

Ray versus mode differences in reverberation modeling solutions for environments with high boundary scattering loss

Thorsos, E.I., F.S. Henyey, J. Yang, and S.A. Reynolds, "Ray versus mode differences in reverberation modeling solutions for environments with high boundary scattering loss," J. Acoust. Soc. Am., 126, 2209, doi:10.1121/1.3248702, 2009.

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1 Oct 2009

Several of the problems for the first Reverberation Modeling Workshop yielded interesting differences between solutions obtained with ray and normal mode methods. These particular problems were defined with high boundary scattering loss. A bottom reverberation case at 3.5 kHz with a down-refracting sound speed profile (Problem VI) will be considered as a case in point. The ray solutions show a "direct path" contribution unaffected by the bottom scattering loss as long as a direct path can reach the bottom, while the mode solutions obtained to date show a lower reverberation level during this period due to modal attenuation. These differences occur in both incoherent and coherent reverberation solutions for both rays and modes. Arguments will be presented that indicate the correctness of the ray solutions for this case. Suggestions will also be made on how the mode approach can be used to obtain solutions in agreement with the ray method.

Single-path acoustic scintillation results from the Shallow Water 2006 Experiment

Tang, D., D. Rouseff, F. Henyey, and J. Yang, "Single-path acoustic scintillation results from the Shallow Water 2006 Experiment," J. Acoust. Soc. Am.,126, 2172, doi:10.1121/1.3248459, 2009.

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1 Oct 2009

In "sound transmission through a fluctuating ocean," Flattxe et al. described saturation of a single acoustic path as that path becoming a number of interfering uncorrelated micropaths due to refraction by internal waves. The probability density function of intensity becomes exponential with a scintillation index of 1.0. In deep water, however, full saturation is not achieved due to weak scattering and absorption.

Mid-frequency (1–10 kHz) data from the Shallow Water 2006 Experiment are used to determine single-path intensity statistics. At a range of 1 km in water 80 m deep, an acoustic path is isolated that went through two upper turning points separated by a single bottom reflection. The data were collected during a period when large nonlinear internal waves were absent. The scintillation index calculated from the data increases with frequency until reaching a maximum of 1.2 around 6 kHz. It then decreases to 1.0, suggesting that single-path saturation can be achieved at mid-frequencies in shallow water. The probability density functions of intensity at various frequencies show a trend toward exponential. Because shallow water internal waves are dominated by the first mode, uncorrelated micropaths are an unlikely mechanism for producing the observed saturation.

Anomalous dispersion and pulse propagation in oceanic bubble clouds

Henyey, F.S., "Anomalous dispersion and pulse propagation in oceanic bubble clouds," J. Acoust. Soc. Am., 125, 2611, 2009.

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1 Apr 2009

During a planning meeting for the Scripps pier bubble experiment, Ralph Goodman suggested we apply the Kramers–Kronig relations to bubble cloud data. By "we," I assumed he meant that I should do it. I applied the Kramers–Kronig relations to David Farmer's Scripps pier data from his modified Medwin resonators. This allowed a determination on which data had lower accuracy than the rest. Using the high accuracy data, I constructed a model of the complex sound speed. No formula relating bubble size distributions was needed. This model has anomalous dispersion in a frequency band that nearly coincides with a region in which the group speed is higher than the sound speed in bubble-free water. Summerfeld's theorem prohibits any signal from traveling that fast. The consequences for pulse propagation within bubble clouds was determined, using pulses having the same frequency spectrum as transmitted by Jerry Caruthers. The predicted nature of the received pulse is only partially described by Brillouin's studies, done before computers existed.

Measurements of acoustic propagation with accompanying high-resolution sound speed structure containing internal waves

Henyey, F.S., K.L. Williams, and D. Tang, "Measurements of acoustic propagation with accompanying high-resolution sound speed structure containing internal waves," J. Acoust. Soc. Am., 125, 2512, 2009.

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1 Apr 2009

During the Shallow Water 2006 experiment, simultaneous measurements were made of the sound speed structure associated with nonlinear internal waves and acoustic propagation at frequencies of 2–10 kHz over a 1 km path. The internal waves were measured by a towed CTD chain in order to get high resolution. These measurements were coordinated so that the nonlinear waves can be interpolated onto the acoustic path, allowing predictions of their effects on the acoustics. An internal wave train was measured that passed the acoustic path on August 13. When the wave train was in between the sound source and receiver, distinctive arrival time oscillations on three acoustic paths were measured, which are all rays having an upper turning point. Using the CTD chain data, a deterministic explanation is given to the arrival time oscillations.

Mid-frequency acoustic propagation in shallow water on the New Jersey shelf. II: Intensity fluctuation

Tang, D., F.S. Henyey, Z. Wang, K.L. Williams, D. Rouseff, P.H. Dahl, J. Quijano, and J.W. Choi, "Mid-frequency acoustic propagation in shallow water on the New Jersey shelf. II: Intensity fluctuation," J. Acoust. Soc. Am., 124, EL91-EL96, 2008.

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28 Aug 2008

The scintillation index and the intensity cumulative distribution function of mid-frequency (2–10 kHz) sound propagation are presented at ranges of 1–9 km in a shallow water channel. The fluctuations are due to water column sound speed variability. It is found that intensity is only correlated over a narrow frequency band (50–200 Hz) and the bandwidth is independent of center frequency and range. Furthermore, the intensity probability distribution peaks at zero for all frequencies, and follows an exponential distribution at small values.

Mid-frequency acoustic propagation in shallow water on the New Jersey shelf: Mean intensity

Tang, D., F.S. Henyey, Z. Wang, K.L. Williams, D. Rouseff, P.H. Dahl, J. Quijano, and J.W. Choi, "Mid-frequency acoustic propagation in shallow water on the New Jersey shelf: Mean intensity," J. Acoust. Soc. Am., 124, EL85-EL90, 2008.

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28 Aug 2008

Mid-frequency (1–10 kHz) sound propagation was measured at ranges 1–9 km in shallow water in order to investigate intensity statistics. Warm water near the bottom results in a sound speed minimum. Environmental measurements include sediment sound speed and water sound speed and density from a towed conductivity-temperature-depth chain. Ambient internal waves contribute to acoustic fluctuations. A simple model involving modes with random phases predicts the mean transmission loss to within a few dB. Quantitative ray theory fails due to near axial focusing. Fluctuations of the intensity field are dominated by water column variability.

Fluctuation of mid-frequency propagation in shallow water

Tang, D., F.S. Henyey, K.L. Williams, D. Rouseff, P.H. Dahl, Z. Wang, J.E. Quijano, and J.W. Choi, "Fluctuation of mid-frequency propagation in shallow water," J. Acoust. Soc. Am., 123, 3433, 2008.

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1 May 2008

As part of the ONR-sponsored SW06 experiment, mid-frequency sound propagation was measured at ranges 1–10 km in the frequency band of 2–10 kHz in August, 2006. The water depth is 80 m and the source depth is 30 m, close to the minimum of a duct with a thermocline above and a warm salty water below. The receivers are clustered into two groups, one at 25 m depth, the other at 50 m. The region has active internal wave activity during this time. Because the source is near the axis of the sound channel, it is observed that propagation is dominated by trapped modes and behaves similar to sound propagation in a deep water duct. Amplitude fluctuations and cross-frequency correlations are estimated. The scintillation index as a function of frequency and bandwidth is calculated.

Simultaneous nearby measurements of acoustic propagation and high-resolution sound speed structure containing internal waves

Henyey, F.S., K.L. Williams, and D. Tang, "Simultaneous nearby measurements of acoustic propagation and high-resolution sound speed structure containing internal waves," J. Acoust. Soc. Am., 123, 3588, 2008

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1 May 2008

On two occasions during the SW06 experiment, towed CTD chain measurements were made close to an acoustic propagation path. The acoustic path was 1 km long, oriented roughly in the direction of propagation of large nonlinear internal waves. On the first occasion, large nonlinear internal waves were absent, and on the second occasion, they were present. The CTD chain was towed in loops around the acoustic path, roughly 200 m on either side of the path. On the first occasion, 17 loops were made in about 5.5 hr, and on the second occasion, 7 loops were made in about 2.5 hr. Throughout these time periods, acoustic transmissions between 2 kHz and 10 kHz were carried out. The acoustic environment on the path is estimated by space and time interpolation between the tows on the two sides of the path. The acoustic data is compared with propagation modeling in this environment.

Unperturbed normal mode method for forward surface scattering

Henyey, F.S., and E. Thorsos, "Unperturbed normal mode method for forward surface scattering," J. Acoust. Soc. Am., 123, 3086, 2008.

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1 May 2008

A technique is presented that uses an expansion in unperturbed modes to calculate acoustic scattering from ocean surface waves in a shallow water waveguide. The basic formalism as well as a useful extension to account for the difference between the water column and the domain in which the modes are calculated. The coupling between the modes due to the waves is local at the ocean surface, unlike the coupling of local modes. Numerical examples of the calculation are given for both a sinusoid surface wave and a random surface wave with a typical wind driven spectrum.

High-frequency internal waves on the Oregon continental shelf

D'Asaro, E.A., R.-C. Lien, and F. Henyey, "High-frequency internal waves on the Oregon continental shelf," J. Phys. Oceanogr., 37, 195601976, doi:10.1175/JPO3096.1, 2007.

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1 Jul 2007

Measurements of vertical velocity by isopycnal-following, neutrally buoyant floats deployed on the Oregon shelf during the summers of 2000 and 2001 were used to characterize internal gravity waves on the shelf using measurements of vertical velocity. The average spectrum of Wentzel–Kramers–Brillouin (WKB)-scaled vertical kinetic energy has the level predicted by the Garrett–Munk model (GM79), plus a narrow M2 tidal peak and a broad high-frequency peak extending from about 0.1N to N and rising a decade above GM79. The high-frequency peak varies in energy coherently with time across its entire bandwidth. Its energy is independent of the tidal energy. The energy in the "continuum" region between the peaks is weakly correlated with the level of the high-frequency peak energy and is independent of the tidal peak energy. The vertical velocity is not Gaussian but is highly intermittent, with a calculated kurtosis of 19. The vertical kinetic energy varies geographically. Low energy is found offshore and nearshore. The highest energy is found near a small seamount. High energy is found over the rough topography of Heceta Bank and near the shelf break. The highest energy occurs as packets of high-frequency waves, often occurring on the sharp downward phase of the M2 internal tide and called "tidal solibores."

A few isolated waves with high energy are also found. Of the 1-h periods with the highest vertical kinetic energy, 31% are tidal solibores, 8% are isolated waves, and the remainder of the periods appear unorganized. The two most energetic tidal solibores were examined in detail. As compared with the steady, propagating, two-dimensional, inviscid, internal-wave solutions to the equations of motion with no background shear [i.e., the Dubreil–Jacotin–Long (DJL) equation], all but the most energetic observed waveforms are too narrow for their height to be solitary waves. Despite the large near-N peak in vertical kinetic energy, the M2 internal tide contributes over 80% of the energy, ignoring near-inertial waves. The tidal solibores make a very small contribution, 0.5%, to the overall internal-wave energy.

Mean acoustic field in long-range ocean acoustic propagation experiment (LOAPEX)

Andrew, R.K., F.S. Henyey, J.A. Mercer, B.M. Howe, P.F. Worcester, and M.A. Dzieciuch, "Mean acoustic field in long-range ocean acoustic propagation experiment (LOAPEX)," J. Acoust. Soc. Am., 120, 3021, 2006.

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1 Nov 2006

We extract the low-frequency (70 Hz) mean acoustic pressure field, and the mean acoustic field up to time shifts, from the LOAPEX receptions on the vertical line arrays, for transmissions at various ranges. Means are taken over time intervals of order a day. Source and receiver motion is removed from the data, and possibly tides and other slow phenomena. The experimental results are compared to predictions from theoretical calculations assuming scattering by internal waves. The theoretical calculations make the Markov approximation that the sound-speed fluctuation correlations can be replaced by an operator at a single range. The calculations use modes rather than rays, because of the very low frequency, thus differing from the version of the Markov approximation that assumes delta-correlated sound-speed fluctuations.

Effect of shallow water internal waves on the ambient noise notch

Rouseff, D., D. Tang, and F.S. Henyey, "Effect of shallow water internal waves on the ambient noise notch," J. Acoust. Soc. Am., 117, 2577, doi: 10.1121/1.1841692, 2005.

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1 Aug 2005

Coherent underwater communication is hampered by the time spread inherent to acoustic propagation in the ocean. Because time-reversal signal processing produces pulse compression, communications has been suggested as a natural application of the technique. Passive versions of time-reversal processing use a receive-only array to do combined temporal and spatial matched filtering. It can be shown, however, that the pulse compression it achieves is not perfect and that an equalizer that relies solely on time-reversal processing will have an error floor caused by uncompensated intersymbol interference (ISI). In the present paper, a physics-based model is developed for the uncompensated ISI in a passive time-reversal equalizer. The model makes use of a normal-mode expansion for the acoustic field. The matched-filtering integral is approximated and the intermediate result interpreted using the waveguide invariant. After combining across the array and sampling, formal statistical averages of the soft demodulation output are calculated. The results show how performance scales with bandwidth, with the number and position of array elements, and with the length of the finite impulse response matched filters. Good agreement is obtained between the predicted scaling and that observed in field experiments.

Internal wave effects on high frequency acoustic propagation to horizontal arrays--Experiment and implications to imaging

Williams, K.L., F.S. Henyey, D. Rouseff, S.A. Reynolds, and T.E. Ewart, "Internal wave effects on high frequency acoustic propagation to horizontal arrays--Experiment and implications to imaging," IEEE J. Ocean. Eng., 26, 102-113, 2001.

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1 Jan 2001

An experiment was carried out over a nine day period from August 18 to 27, 1996 to examine acoustic wave propagation in random media at frequencies applicable to synthetic aperture sonar. The objective was to test experimentally the hypothesized imaging effects of variations in the sound speed along two different acoustic paths as put forth by F.S. Henyey et al. (1997). The focus of this paper is on describing the experiment and carrying out an initial analysis of the data in the context of the effect of ocean internal waves on imaging resolution. The oceanography is summarized to the extent needed to discuss important aspects relative to the acoustics experiment. In the acoustics experiment transmissions at 6, 20, 75, and 129 kHz between sources and receiver arrays were carried out. Source to receiver separation was about 815 m. All sources and receivers were mounted on bottom-deployed towers and were at least 9 m off the seafloor. The analysis concentrates on the 75-kHz data acquired during one day of the experiment. The time span examined Is sufficient to examine a diurnal tidal cycle of the oceanographic conditions. The results indicate the IW phase perturbations would have a significant effect on imaging for even the most benign conditions of the experiment if no autofocusing scheme is used. Also, though autofocusing should be useful in recovering the focus for these conditions, there are conditions (e.g., for the path that has a turning point at the thermocline and during times when solibores are present), where more sophisticated compensation schemes would be needed.

Tomographic reconstruction of shallow water bubble fields

Rouseff, D., F.S. Henyey, J.W. Caruthers, and S.J. Stanic, "Tomographic reconstruction of shallow water bubble fields," IEEE J. Ocean. Eng., 26, 131-140, 2001.

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1 Jan 2001

In March of 1997, a shallow water experiment was conducted near the Scripps Pier in La Jolla, CA, USA. The goal was to determine the dynamics, distribution, and acoustic effects of bubbles just offshore from active surf. A major component of the experiment was the "Delta Frame," an apparatus that supported two acoustic sources and eight receivers. Acoustic intensity was measured at frequencies between 39 and 244 kHz over the resulting 16 horizontal ray paths. Paths ranged in length from 2.5 to 8.6 m. In the present paper, a tomography algorithm is developed and implemented using Delta Frame data. Measurements are combined to produce quantitative cross-sectional images of the attenuation associated with the bubble cloud. Numerical simulations predict that the Frame ran resolve details of the field down to about 2 m. Images constructed at different acoustic frequencies are scaled and compared. A 5-min sequence of images is studied in detail. Swell waves are shown to cause rapid fluctuations in the images.

The dependence of low-frequency underwater surface scattering on remotely sensed oceanographic variables

Gaus, R.C., E.I. Thorsos, F.S. Henyey, and J.M. Fialkowski, "The dependence of low-frequency underwater surface scattering on remotely sensed oceanographic variables," J. Acoust. Soc. Am., 108, 2585, 2000.

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1 Nov 2000

Recent low-frequency (<1500 Hz) underwater acoustic measurements have demonstrated that scattering processes at the air–sea interface depend primarily on the wind speed and the surface wave spectrum. The scattering strength from the rough interface is proportional to the spectral density at the Bragg wavelength with modifications due to tilt and modulation by longer waves. These modifications are accounted for in the small slope approximation. When wave breaking becomes significant, rough interface scattering is augmented by bubble cloud scattering, which depends primarily on wind speed. In this regime, bubble cloud scattering dominates at low grazing angles, and rough interface scattering dominates at high grazing angles. A physics-based empirical model is used to describe bubble scattering. The mean-frequency-shift characteristics of acoustic signals scattered from both the moving sea surface and bubble clouds have been successfully modeled given the 2-D surface wave spectrum. These scattering-strength and frequency-shift models are used to explore the sensitivity of low-frequency scattering to environmental variables obtainable by remote sensing.

Clebsch representation near points where the vorticity vanishes

Graham, C.R., and F.S. Henyey, "Clebsch representation near points where the vorticity vanishes," Phys. Fluids, 12, 744-746, 2000.

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1 Apr 2000

We demonstrate that there is no Clebsch representation in any neighborhood of a generic vanishing point of the vorticity. This result is placed in the context of the Hamiltonian formulation of fluid mechanics. For stratified fluids, the analogous representation does exist, both locally and globally, under suitable hypotheses.

Reconstruction of evolving shallow water bubble clouds by acoustic tomography

Rouseff, D., S.G. Kargl, F.S. Henyey, and J.W. Caruthers, "Reconstruction of evolving shallow water bubble clouds by acoustic tomography," Acoustical Imaging Vol. 25, edited by M. Halliwell and P.N.T. Well, 225-228 (Kluwer Academic/Plenum Publishers, New York, 2000).

15 Jan 2000

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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