Lynch James F.

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Report on the Office of Naval Research Shallow-Water Acoustic Workshop 1-3 October 1996

(Woods Hole Oceanographic Institution, 1997-06) Lynch, James F.

The results of an unclassified workshop on Shallow Water Acoustics, jointly sponsored by ONR and DARPA, are presented. The workshop was held on October 1-3, 1996 at the Naval Research Laboratory, Stennis Space Center, and included 83 participants specializing in ocean acoustics, geology and geophysics, physical oceanography, and other disciplines relevant to shallow water research. The goal of the workshop was to help determine the current status of and future directions for shallow water acoustics research. The report summarizes the deliberations and recommendations of the workshop, and includes detailed report from the three working groups (bottom, water column, and modeling and signal processing) as well as from the workshop moderator (Dr. James Lynch, WHOI).
Long distance passive localization of vocalizing sei whales using an acoustic normal mode approach

(Acoustical Society of America, 2012-02) Newhall, Arthur E. ; Lin, Ying-Tsong ; Lynch, James F. ; Baumgartner, Mark F. ; Gawarkiewicz, Glen G.

During a 2 day period in mid-September 2006, more than 200, unconfirmed but identifiable, sei whale (Balaenoptera borealis) calls were collected as incidental data during a multidisciplinary oceanography and acoustics experiment on the shelf off New Jersey. Using a combined vertical and horizontal acoustic receiving array, sei whale movements were tracked over long distances (up to tens of kilometers) using a normal mode back propagation technique. This approach uses low-frequency, broadband passive sei whale call receptions from a single-station, two-dimensional hydrophone array to perform long distance localization and tracking by exploiting the dispersive nature of propagating normal modes in a shallow water environment. The back propagation approach is examined for accuracy and application to tracking the sei whale vocalizations identified in the vertical and horizontal array signals. This passive whale tracking, combined with the intensive oceanography measurements performed during the experiment, was also used to examine sei whale movements in relation to oceanographic features observed in this region.
Acoustic intensity fluctuations induced by South China Sea internal tides and solitons

(IEEE, 2004-10) Chiu, Ching-Sang ; Ramp, Steven R. ; Miller, Christopher W. ; Lynch, James F. ; Duda, Timothy F. ; Tang, Tswen Yung

Between late April and May 23, 2001, a suite of acoustic and oceanographic sensors was deployed by a team of U.S., Taiwan, and Singapore scientists in the northeastern South China Sea to study the effects of ocean variability on low-frequency sound propagation in a shelfbreak environment. The primary acoustic receiver was an L-shaped hydrophone array moored on the continental shelf that monitored a variety of signals transmitted along and across the shelfbreak by moored sources. This paper discusses and contrasts the fluctuations in the 400-Hz signals transmitted across the shelfbreak and measured by the vertical segment of the listening array on two different days, one with the passage of several huge solitons that depressed the shallow isotherms to near the sea bottom and one with a much less energetic internal wavefield. In addition to exhibiting large and rapid temporal changes, the acoustic data show a much more vertically diffused sound intensity field as the huge solitons occupied and passed through the transmission path. Using a space-time continuous empirical sound-speed model based on the moored temperature records, the observed acoustic intensity fluctuations are explained using coupled-mode physics.
High-frequency side-scan sonar fish reconnaissance by autonomous underwater vehicles

( 2016-05) Grothues, Thomas ; Newhall, Arthur E. ; Lynch, James F. ; Vogel, Kaela S. ; Gawarkiewicz, Glen G.

A dichotomy between depth penetration and resolution as a function of sonar frequency, draw resolution, and beam spread challenges fish target classification from sonar. Moving high-frequency sources to depth using autonomous underwater vehicles (AUVs) mitigates this and also co-locates transducers with other AUV-mounted short-range sensors to allow a holistic approach to ecological surveys. This widely available tool with a pedigree for bottom mapping is not commonly applied to fish reconnaissance and requires the development of an interpretation of pelagic reflective features, revisitation of count methods, image-processing rather than wave-form recognition for automation, and an understanding of bias. In a series of AUV mission test cases, side-scan sonar (600 and 900 kHz) returns often resolved individual school members, spacing, size, behavior, and (infrequently) species from anatomical features and could be intuitively classified by ecologists — but also produced artifacts. Fish often followed the AUV and thus were videographed, but in doing so removed themselves from the sonar aperture. AUV-supported high-frequency side-scan holds particular promise for survey of scarce, large species or for synergistic investigation of predators and their prey because the spatial scale of observations may be similar to those of predators.
Preliminary acoustic and oceanographic observations from the ASIAEX 2001 South China Sea Experiment

(Woods Hole Oceanographic Institution, 2001-09) Newhall, Arthur E. ; Costello, Lawrence ; Duda, Timothy F. ; Dunn, James M. ; Gawarkiewicz, Glen G. ; Irish, James D. ; Kemp, John N. ; McPhee, Neil M. ; Liberatore, Stephen P. ; Lynch, James F. ; Ostrom, William M. ; Schroeder, Ted ; Trask, Richard P. ; von der Heydt, Keith

The Asian Seas International Experiment (ASIAEX) was a very successful scientific collaboration between the United States of America (USA), the People’s Republic of China (PRC), Taiwan (ROC), the Republic of Korea (ROK), Japan, Russia, and Singapore. Preliminary field experiments associated with ASIAEX began in spring of 2000. The main experiments were performed in April-August, 2001. The scientific plan called for two major acoustics experiments, the first a bottom interaction experiment in the East China Sea (ECS) and the second a volume interaction experiment in the South China Sea (SCS). In addition to the acoustics efforts, there were also extremely strong physical oceanography and geology and geophysics components to the experiments. This report will concentrate on describing the moored component of the South China Sea portion of ASIAEX 2001 performed from the Taiwan Fisheries research vessel FR1 (Fisheries Researcher 1). Information on the environmental moorings deployed from the Taiwanese oceanographic research vessel OR1 (Oceanographic Researcher 1) will also be listed here for completeness, so that the reader can pursue later analyses of the data. This report does not pursue any data analyses per se.
Winter 1993 observations of oceanography and sediment transport at the LEO-15 site

(Woods Hole Oceanographic Institution, 1995-12) Irish, James D. ; Lynch, James F. ; Newhall, Arthur E. ; Witzell, Nick ; Traykovski, Peter A. ; Glenn, Scott M.

The NOAA National Underseas Research Program at Rutgers University is establishing a Long-term Ecosystem Observatory off New Jersey in 15 meters of water. As part of a bottom boundary layer study at this site, WHOI deployed a bottom instrument frame during the winter of 1993-94. The bottom instrument carried a current meter, a vertical array of optical back scattering sensors, temperature, pressure and conductivity sensors and an Acoustical Backscattering Sensor. The deployment was partially successful as the acoustic system failed. The other instrumentation worked well for 3 weeks returning data on winter conditions at the site. The extreme winter waves ended the experiment by tipping the instrument over on its side. The optical instrumentation was calibrated with sediment from the site, and the results from the experiment presented.
Enhanced acoustic mode coupling resulting from an internal solitary wave approaching the shelfbreak in the South China Sea

(Acoustical Society of America, 2013-03) Chiu, Linus Y. S. ; Reeder, D. Benjamin ; Chang, Yuan-Ying ; Chen, Chi-Fang ; Chiu, Ching-Sang ; Lynch, James F.

Internal waves and bathymetric variation create time- and space-dependent alterations in the ocean acoustic waveguide, and cause subsequent coupling of acoustic energy between propagating normal modes. In this paper, the criterion for adiabatic invariance is extended to the case of an internal solitary wave (ISW) encountering a sloping bathymetry (i.e., continental shelfbreak). Predictions based on the extended criterion for adiabatic invariance are compared to experimental observations from the Asian Seas International Acoustics Experiment. Using a mode 1 starter field, results demonstrate time-dependent coupling of mode 1 energy to higher adjacent modes, followed by abrupt coupling of mode 5–7 energy to nonadjacent modes 8–20, produces enhanced mode coupling and higher received levels downrange of the oceanographic and bathymetric features. Numerical simulations demonstrate that increasing ISW amplitude and seafloor slope enhance the coupling of energy to adjacent and nonadjacent modes. This enhanced coupling is the direct result of the simultaneous influence of the ISW and its proximity to the shelfbreak, and, compared to the individual effect of the ISW or shelfbreak, has the capacity to scatter 2–4 times the amount of acoustic energy from below the thermocline into the upper water column beyond the shelfbreak in realistic environments.
A report on the 3-D acoustic working group meeting at Long Beach, MS July 7-8, 1988

(Woods Hole Oceanographic Institution, 1989-06) Lynch, James F. ; Chiu, Ching-Sang

At the request of ONR Code 11250A, the Woods Hole Oceanographic Institution (Dr. James F. Lynch) convened a workshop to bring together a group of acoustic and ocean modelers to review and discuss 1. the state of development and the need for three-dimensional numerical acoustic research propagation and scattering models; 2. the interfacing of acoustic models with available oceanographic data and ocean model outputs. The workshop was hosted by the Institute for Naval Oceanography (Dr. Ching-Sang Chiu) at Long Beach, MS on July 7-8, 1988. This report summarizes the research presentations and the recommendations made by the group. The workshop was an initial attempt to promote the interaction between the ocean and acoustic modeling communities. This interaction between the communities is essential to the development of truly interactive basic research acoustic and ocean models. We anticipate more workshops of such nature to be held in the future. The findings and recommendations generated by these workshops are expected to have a strong impact on the direction of future three-dimensional modeling research in both acoustics and oceanography .
Acoustic ducting, reflection, refraction, and dispersion by curved nonlinear internal waves in shallow water

(IEEE Oceanic Engineering Society, 2010-02-08) Lynch, James F. ; Lin, Ying-Tsong ; Duda, Timothy F. ; Newhall, Arthur E.

Nonlinear internal waves in shallow water have been shown to be effective ducts of acoustic energy, through theory, numerical modeling, and experiment. To date, most work on such ducting has concentrated on rectilinear internal wave ducts or those with very slight curvature. In this paper, we examine the acoustic effects of significant curvature of these internal waves. (By significant curvature, we mean lateral deviation of the internal wave duct by more than half the spacing between internal waves over an acoustic path, giving a transition from ducting to antiducting.) We develop basic analytical models of these effects, employ fully 3-D numerical models of sound propagation and scattering, and examine simultaneous acoustical and oceanographic data from the 2006 Shallow Water Experiment (SW06). It will be seen that the effects of curvature should be evident in the mode amplitudes and arrival angles, and that observations are consistent with curvature, though with some possible ambiguity with other scattering mechanisms.
Experimental and numerical studies of sound propagation over a submarine canyon northeast of Taiwan

(IEEE, 2015-01-09) Lin, Ying-Tsong ; Duda, Timothy F. ; Emerson, Chris ; Gawarkiewicz, Glen G. ; Newhall, Arthur E. ; Calder, Brian ; Lynch, James F. ; Abbot, Philip A. ; Yang, Yiing-Jang ; Jan, Sen

A study of sound propagation over a submarine canyon northeast of Taiwan was made using mobile acoustic sources during a joint ocean acoustic and physical oceanographic experiment in 2009. The acoustic signal levels (equivalently, transmission losses) are reported here, and numerical models of 3-D sound propagation are employed to explain the underlying physics. The data show a significant decrease in sound intensity as the source crossed over the canyon, and the numerical model provides a physical insight into this effect. In addition, the model also suggests that reflection from the canyon seabed causes 3-D sound focusing when the direction of propagation is along the canyon axis, which remains to be validated in a future experiment. Environmental uncertainties of water sound speed, bottom geoacoustic properties, and bathymetry are addressed, and the implications for sound propagation prediction in a complex submarine canyon environment are also discussed.
Underwater acoustics research at the Woods Hole Oceanographic Institution, 1930-1960

(Acoustical Society of America, 2016-06-23) Lynch, James F. ; Newhall, Arthur E. ; Frosch, Robert A.

The Woods Hole Oceanographic Institution (WHOI) was founded in 1930, and throughout its history has had a strong involvement in research into the science and applications of sound in the ocean. In terms of a brief history, three eras stand out: (1) pre-WWII, (2) WWII, and (3) the postwar years. This manuscript will focus on the history of the most influential and colorful, individuals and stories that arose during the war years. Provided are personal reminiscences, technical report details, and photos illustrating the achievements, and importance, in underwater sound research at WHOI during that time.
Horizontal refraction of propagating sound due to seafloor scours over a range-dependent layered bottom on the New Jersey shelf

(Acoustical Society of America, 2012-04) Ballard, Megan S. ; Lin, Ying-Tsong ; Lynch, James F.

Three-dimensional propagation effects of low frequency sound from 100 to 400 Hz caused by seafloor topography and range-dependent bottom structure over a 20 km range along the New Jersey shelf are investigated using a hybrid modeling approach. Normal modes are used in the vertical dimension, and a parabolic-equation approximate model is applied to solve the horizontal refraction equation. Examination of modal amplitudes demonstrates the effect of environmental range dependence on modes trapped in the water column, modes interacting with the bottom, and modes trapped in the bottom. Using normal mode ray tracing, topographic features responsible for three-dimensional effects of horizontal refraction and focusing are identified. These effects are observed in the measurements from the Shallow Water 2006 experiment. Specifically, signals from a pair of fixed sources recorded on a horizontal line array sitting on the seafloor show an intensification caused by horizontal focusing due to the seabed topography of 4 dB along the array.
Observed limiting cases of horizontal field coherence and array performance in a time-varying internal wavefield

(Acoustical Society of America, 2008-08-28) Collis, Jon M. ; Duda, Timothy F. ; Lynch, James F. ; DeFerrari, Harry A.

Using a moored source and horizontal/vertical line array combination, horizontal coherence properties of high signal to noise ratio (>=20 dB) 100–1600 Hz signals have been measured. Internal waves in the area of the measurement created moving episodic sound-speed anomaly structures, influencing coherence length. Measured horizontal coherence scales for 100 Hz ranged from 5 to 20 acoustic wavelengths, and were inversely related to the sound-speed anomaly strength. Horizontal field properties were compared with fields computed using modal decompositions of the vertical signals. The comparison allows azimuthal field coherence properties to be studied apart from normal-mode interference effects.
Estimate of the bottom compressional wave speed profile in the northeastern South China Sea using "Sources of Opportunity"

(IEEE, 2004-10) Lin, Ying-Tsong ; Lynch, James F. ; Chotiros, Nicholas P. ; Chen, Chi-Fang ; Newhall, Arthur E. ; Turgut, Altan ; Schock, Steven G. ; Chiu, Ching-Sang ; Bartek, Louis R. ; Liu, Char-Shine

The inversion of a broad-band "source of opportunity" signal for bottom geoacoustic parameters in the northeastern South China Sea (SCS) is presented, which supplements the towed source and chirp sonar bottom inversions that were performed as part of the Asian Seas International Acoustics Experiment (ASIAEX). This source of opportunity was most likely a "dynamite fishing" signal, which has sufficient low-frequency content (5-500 Hz) to make it complimentary to the somewhat higher frequency J-15-3 towed source (50-260 Hz) signals and the much higher frequency (1-10 kHz) chirp signals. This low frequency content will penetrate deeper into the bottom, thus extending the other inverse results. Localization of the source is discussed, using both a horizontal array for azimuthal steering and the "water wave" part of the pulse arrival for distance estimation. A linear broad-band inverse is performed, and three new variants of the broad-band inverse, based on: 1) the Airy phase; 2) the cutoff frequency; and 3) a range-dependent medium are presented. A multilayer model of the bottom compressional wave speed is obtained, and error estimates for this model are shown, both for the range-independent approximation to the waveguide and for the range-dependent waveguide. Directions for future research are discussed.
Simulated tomographic reconstruction of ocean features using drifting acoustic receivers and a navigated source

(Acoustical Society of America, 1995-10) Duda, Timothy F. ; Pawlowicz, Richard A. ; Lynch, James F. ; Cornuelle, Bruce D.

Numerically simulated acoustic transmission from a single source of known position (for example, suspended from a ship) to receivers of partially known position (for example, sonobuoys dropped from the air) are used for tomographic mapping of ocean sound speed. The maps are evaluated for accuracy and utility. Grids of 16 receivers are employed, with sizes of 150, 300, and 700 km square. Ordinary statistical measures are used to evaluate the pattern similarity and thus the mapping capability of the system. For an array of 300 km square, quantitative error in the maps grows with receiver position uncertainty. The large and small arrays show lesser mapping capability than the mid-size array. Mapping errors increase with receiver position uncertainty for uncertainties less than 1000-m rms, but uncertainties exceeding that have less systematic effect on the maps. Maps of rms error of the field do not provide a complete view of the utility of the acoustic network. Features of maps are surprisingly reproducible for different navigation error levels, and give comparable information about mesoscale structures despite great variations in those levels.
On whether azimuthal isotropy and alongshelf translational invariance are present in low-frequency acoustic propagation along the New Jersey shelfbreak

(Acoustical Society of America, 2012-02) Lynch, James F. ; Emerson, Chris ; Abbot, Philip A. ; Gawarkiewicz, Glen G. ; Newhall, Arthur E. ; Lin, Ying-Tsong ; Duda, Timothy F.

To understand the issues associated with the presence (or lack) of azimuthal isotropy and horizontal (along isobath) invariance of low-frequency (center frequencies of 600 Hz and 900 Hz) acoustic propagation in a shelfbreak environment, a series of experiments were conducted under the Autonomous Wide-Aperture Cluster for Surveillance component of the Shallow Water 2006 experiment. Transmission loss data reported here were from two mobile acoustic sources executing (nearly) circular tracks transmitting to sonobuoy receivers in the circle centers, and from one 12.5 km alongshelf acoustic track. The circle radii were 7.5 km. Data are from September 8, 2006. Details of the acoustic and environmental measurements are presented. Simple analytic and computer models are used to assess the variability expected due to the ocean and seabed conditions encountered. A comparison of model results and data is made, which shows preliminary consistency between the data and the models, but also points towards further work that should be undertaken specifically in enlarging the range and frequency parameter space, and in looking at integrated transmission loss.
Shelf-edge frontal structure in the central East China Sea and its impact on low-frequency acoustic propagation

(IEEE, 2004-10) Ramp, Steven R. ; Chiu, Ching-Sang ; Bahr, Frederick L. ; Qi, Yiquan ; Dahl, Peter H. ; Miller, James H. ; Lynch, James F. ; Zhang, Renhe ; Zhou, Ji-Xun

Two field programs, both parts of the Asian Seas International Acoustics Experiment (ASIAEX), were carried out in the central East China Sea (28 to 30 N, 126 30 to 128 E) during April 2000 and June 2001. The goal of these programs was to study the interactions between the shelf edge environment and acoustic propagation at a wide range of frequencies and spatial scales. The low-frequency across-slope propagation was studied using a synthesis of data collected during both years including conductivity- temperature-depth (CTD) and mooring data from 2000, and XBT, thermistor chain, and wide-band source data from 2001. The water column variability during both years was dominated by the Kuroshio Current flowing from southwest to northeast over the continental slope. The barotropic tide was a mixed diurnal/semidiurnal tide with moderate amplitude compared to other parts of the Yellow and East China Sea. A large amplitude semidiurnal internal tide was also a prominent feature of the data during both years. Bursts of high-frequency internal waves were often observed, but these took the form of internal solitons only once, when a rapid off-shelf excursion of the Kuroshio coincided with the ebbing tide. Two case studies in the acoustic transmission loss (TL) over the continental shelf and slope were performed. First, anchor station data obtained during 2000 were used to study how a Kuroshio warm filament on the shelf induced variance in the transmission loss (TL) along the seafloor in the NW quadrant of the study region. The corresponding modeled single-frequency TL structure explained the significant fine-scale variability in time primarily by the changes in the multipath/multimode interference pattern. The interference was quite sensitive to small changes in the phase differences between individual paths/modes induced by the evolution of the warm filament. Second, the across-slope sound speed sections from 2001 were used to explain the observed phenomenon of abrupt signal attenuation as the transmission range lengthened seaward across the continental shelf and slope. This abrupt signal degradation was caused by the Kuroshio frontal gradients that produced an increasingly downward-refracting sound-speed field seaward from the shelf break. This abrupt signal dropout was explained using normal mode theory and was predictable and source depth dependent. For a source located above the turning depth of the highest-order shelf-trapped mode, none of the propagating modes on the shelf were excited, causing total signal extinction on the shelf.
Internal solitons in the ocean

(Woods Hole Oceanographic Institution, 2006-01) Apel, J. R. ; Ostrovsky, Lev A. ; Stepanyants, Y. A. ; Lynch, James F.

Nonlinear internal waves in the ocean are discussed (a) from the standpoint of soliton theory and (b) from the viewpoint of experimental measurements. First, theoretical models for internal solitary waves in the ocean are briefly described.Various nonlinear analytical solutions are treated, commencing with the well-known Boussinesq and Korteweg-deVries equations. Then certain generalizations are considered, including effects of cubic nonlinearity, Earth's rotation, cylindrical divergence, dissipation, shear flows, and others. Recent theoretical models for strongly nonlinear internal waves are outlined. Second, examples of experimental evidence for the existence of solitons in the upper ocean are presented; the data include radar and optical images and in situ measurements of waveforms, propagation speeds, and dispersion characteristics. Third, and finally, action of internal solitons on sound wave propagation is discussed. This review paper is intended for researchers from diverse backgrounds, including acousticians, who may not be familiar in detail with soliton theory. Thus, it includes an outline of the basics of soliton theory. At the same time, recent theoretical and observational results are described which can also make this review useful for mainstream oceanographers and theoreticians.
Overview of results from the Asian Seas International Acoustics Experiment in the East China Sea

(IEEE, 2004-10) Dahl, Peter H. ; Zhang, Renhe ; Miller, James H. ; Bartek, Louis R. ; Peng, Zhauhui ; Ramp, Steven R. ; Zhou, Ji-Xun ; Chiu, Ching-Sang ; Lynch, James F. ; Simmen, Jeffrey A. ; Spindel, Robert C.

The Asian Seas International Acoustics Experiment (ASIAEX) included two major field programs, one in the South China Sea and the other in the East China Sea (ECS). This paper presents an overview of research results from ASIAEX ECS conducted between May 28 and June 9, 2001. The primary emphasis of the field program was shallow-water acoustic propagation, focused on boundary interaction and geoacoustic inversion. The study area's central point was located at 29/spl deg/ 40.67'N, 126/spl deg/ 49.39'E, which is situated 500 km east of the Chinese coastline off Shanghai. The acoustic and supporting environmental measurements are summarized, along with research results to date, and references to papers addressing specific issues in more detail are given.
Three-dimensional coupled mode analysis of internal-wave acoustic ducts

(Acoustical Society of America, 2014-05) Shmelev, Alexey A. ; Lynch, James F. ; Lin, Ying-Tsong ; Schmidt, Henrik

A fully three-dimensional coupled mode approach is used in this paper to describe the physics of low frequency acoustic signals propagating through a train of internal waves at an arbitrary azimuth. A three layer model of the shallow water waveguide is employed for studying the properties of normal modes and their coupled interaction due to the presence of nonlinear internal waves. Using a robust wave number integration technique for Fourier transform computation and a direct global matrix approach, an accurate three-dimensional coupled mode full field solution is obtained for the tonal signal propagation through straight and parallel internal waves. This approach provides accurate results for arbitrary azimuth and includes the effects of backscattering. This enables one to provide an azimuthal analysis of acoustic propagation and separate the effects of mode coupled transparent resonance, horizontal reflection and refraction, the horizontal Lloyd's mirror, horizontal ducting and anti-ducting, and horizontal tunneling and secondary ducting.

Lynch James F.

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