Characterization of the Upper Slope Sand Dunes in the South China Sea

LONG-TERM GOALS: Understand, parameterize and predict the impact of physical mechanisms on acoustic propagation in the ocean environment.Award Number: N0001412WX2050

Acoustic scattering by axisymmetric finite-length bodies with application to fish : measurement and modeling

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2002This thesis investigates the complexities of acoustic scattering by finite bodies in general and by fish in particular through the development of an advanced acoustic scattering model and detailed laboratory acoustic measurements. A general acoustic scattering model is developed that is accurate and numerically effcient for a wide range of frequencies, angles of orientation, irregular axisymmetric shapes and boundary conditions. The model presented is an extension of a two-dimensional conformal mapping approach to scattering by irregular, finite-length bodies of revolution. An extensive series of broadband acoustic backscattering measurements has been conducted involving alewife fish (Alosa pseudoharengus), which are morphologically similar to the Atlantic herring (Clupea harengus). A greater-than-octave bandwidth (40-95 kHz), shaped, linearly swept, frequency modulated signal was used to insonify live, adult alewife that were tethered while being rotated in 1-degree increments over all angles of orientation in two planes of rotation (lateral and dorsal/ventral). Spectral analysis correlates frequency dependencies to morphology and orientation. Pulse compression processing temporally resolves multiple returns from each individual which show good correlation with size and orientation, and demonstrate that there exists more than one significant scattering feature in the animaL. Imaging technologies used to exactly measure the morphology of the scattering features of fish include very highresolution Phase Contrast X-rays (PCX) and Computerized Tomography (CT) scans, which are used for morphological evaluation and incorporation into the scattering modeL. Studies such as this one, which combine scattering models with high-resolution morphological information and high-quality laboratory data, are crucial to the quantitative use of acoustics in the ocean

Acoustical characterization of the riverine environment

N0001412WX2151

Non-Rayleigh acoustic scattering characteristics of individual fish and zooplankton

Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 260-268, doi:10.1109/JOE.2004.828208.It has long been known that the statistical properties of acoustic echoes from individual fish can have non-Rayleigh characteristics. The statistical properties of echoes from zooplankton are generally less understood. In this study, echoes from individual fish and zooplankton from a series of laboratory measurements from the past decade are investigated. In the experiments, acoustic echoes from various individual organisms were measured over a wide range of frequencies and orientations, typically in 1/spl deg/-3/spl deg/ increments. In the analysis in this paper, the echoes from most of those measurements are grouped according to ranges of orientation, which correspond to typical orientation distributions of these organisms in the natural ocean environment. This grouping provides a distribution of echo values for each range of orientation. This approach, in essence, emulates a field experiment whereby distributions of echoes would be recorded for different distributions of orientations of the organisms. For both the fish and zooplankton data, there are conditions under which the echoes are strongly non-Rayleigh distributed. In some cases, the distribution is quantitatively connected to the physics of the scattering process while, in other cases, the connection is described qualitatively. Exploitation of the animal-specific statistics for classification purposes is suggested

Acoustic scattering by axisymmertic finite-length bodies with application to fish : measurement and modeling

Thesis (Ph. D.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering and the Woods Hole Oceanographic Institution), 2002.Includes bibliographical references (leaves 140-148).This thesis investigates the complexities of acoustic scattering by finite bodies in general and by fish in particular through the development of an advanced acoustic scattering model and detailed laboratory acoustic measurements. A general acoustic scattering model is developed that is accurate and numerically efficient for a wide range of frequencies, angles of orientation, irregular axisymmetric shapes and boundary conditions. The model presented is an extension of a two-dimensional conformal mapping approach to scattering by irregular, finite-length bodies of revolution. An extensive series of broadband acoustic backscattering measurements has been conducted involving alewife fish (Alosa pseudoharengus), which are morphologically similar to the Atlantic herring (Clupea harengus). A greater-than-octave bandwidth (40-95 kHz), shaped, linearly swept, frequency modulated signal was used to insonify live, adult alewife that were tethered while being rotated in 1-degree increments over all angles of orientation in two planes of rotation (lateral and dorsal/ventral). Spectral analysis correlates frequency dependencies to morphology and orientation. Pulse compression processing temporally resolves multiple returns from each individual which show good correlation with size and orientation, and demonstrate that there exists more than one significant scattering feature in the animal.(cont.) Imaging technologies used to exactly measure the morphology of the scattering features of fish include very high-resolution Phase Contrast X-rays (PCX) and Computerized Tomography (CT) scans, which are used for morphological evaluation and incorporation into the scattering model. Studies such as this one, which combine scattering models with high-resolution morphological information and high-quality laboratory data, are crucial to the quantitative use of acoustics in the ocean.by D. Benjamin Reeder.Ph.D

Observationally constrained modeling of sound in curved ocean internal waves: Examination of deep ducting and surface ducting at short range

Author Posting. © Acoustical Society of America, 2011. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 130 (2011): 1173-1187, doi:10.1121/1.3605565.A study of 400 Hz sound focusing and ducting effects in a packet of curved nonlinear internal waves in shallow water is presented. Sound propagation roughly along the crests of the waves is simulated with a three-dimensional parabolic equation computational code, and the results are compared to measured propagation along fixed 3 and 6 km source/receiver paths. The measurements were made on the shelf of the South China Sea northeast of Tung-Sha Island. Construction of the time-varying three-dimensional sound-speed fields used in the modeling simulations was guided by environmental data collected concurrently with the acoustic data. Computed three-dimensional propagation results compare well with field observations. The simulations allow identification of time-dependent sound forward scattering and ducting processes within the curved internal gravity waves. Strong acoustic intensity enhancement was observed during passage of high-amplitude nonlinear waves over the source/receiver paths, and is replicated in the model. The waves were typical of the region (35 m vertical displacement). Two types of ducting are found in the model, which occur asynchronously. One type is three-dimensional modal trapping in deep ducts within the wave crests (shallow thermocline zones). The second type is surface ducting within the wave troughs (deep thermocline zones).Grants from the Office of Naval Research funded this work. Use of the vessels Ocean Researcher I and Ocean Researcher II in this experiment was funded by the Taiwan National Science Council

Taphonomic Comparisons of Two Laurentian Upper Ordovician Epeiric Sea “Small Shelly Faunas”

The Elgin Member of the Upper Ordovician (Katian) Maquoketa Formation of Iowa contains phosphorite beds consisting of millimeter-scale phosphatic fossils, primarily steinkerns. Similar beds occur in the coeval strata of the classic Cincinnatian Series around the Cincinnati, Ohio area. Initial sampling of the phosphate-rich beds of the Maquoketa allows comparison between the faunal composition and taphonomy of these beds and collections from the more extensively sampled Cincinnatian strata. We isolated these fossils by dissolution of bulk samples in acetic acid and examined the same strata in thin section to study the fossils in context. The Maquoketa diminutive phosphatized fossils have been interpreted as evidence of dwarfed faunas indicative of environmental stress, such as anoxia, which may have also contributed to phosphogenesis. An alternative explanation for the small size is that phosphogenesis was size-selective and that phosphatic particles were concentrated by reworking as less-durable shell material was destroyed. These hypotheses can be tested by examining the fauna for “normal” sized elements. Insoluble residue from sampled phosphate-rich strata in both field areas yields abundant molluscan steinkerns, as well as crinoid columnals, conodonts, scolecodonts, bryozoan zooecia steinkerns and other fossils associated with a normal marine fauna. In Cincinnatian occurrences, the composition of the phosphatic assemblages is variable but is a reflection of the variability of faunal composition seen in these strata rather than an indication of an unusual fauna associated with extreme conditions; most are associated with diverse marine assemblages. Insoluble residues from both areas yield steinkerns that precipitated in small pores within larger skeletons. This phenomenon can be seen in thin section, where phosphate is present within certain parts of the larger preserved skeletons. The maximum size of the steinkerns of the Maquoketa is larger than those of most Cincinnatian occurrences, although size is variable in Cincinnatian occurrences. In Cincinnatian strata the abundance of small phosphatic fossils correlates with evidence for reworking; heavily reworked beds yield the most residue. Examined in thin section, the sampled strata of the Maquoketa appear to be heavily reworked and represent an extreme endmember of this concentration of durable phosphatic material. Detailed examination using an SEM and associated XRF elemental mapping reveals that the phosphatic steinkerns of both localities are very similar in their taphonomy. Both consist of botryoidal growths of carbonate fluorapatite (CFA). The botryoidal growth appears to have nucleated on the walls of the original shell, first forming a lining of variable thickness. Some steinkerns have secondary botryoidal growths on the outside of the steinkern indicating continued precipitation of CFA after destruction of the original shell. This secondary precipitation suggests that reworking played a role not only in concentrating the phosphatic material but also in encouraging continued precipitation of CFA. The size of the available pore space appears to have played a role in encouraging the precipitation of CFA. In thin section the CFA is limited to smaller parts of larger shells, such as the apices of gastropods and did not precipitate on the inside of the larger, more open spaces within the shell. Many of the phosphate-filled spaces are also sediment-filled, suggesting that subdivision of the larger space into smaller pores enhanced the precipitation of CFA. The difference in the maximum size of the steinkern achieved in the different assemblages suggests that geochemical factors affected size limits. The most distinctive aspect of phosphate-rich Ordovician strata of mid-Laurentia is the degree of reworking that concentrated the durable small fossils. Details of taphonomy also suggest that phosphate precipitation was an iterative process enhanced by reworking, and that small pore spaces enhanced this mineralization, thus selectively preserving certain sizes and parts of the larger fauna

Enhanced acoustic mode coupling resulting from an internal solitary wave approaching the shelfbreak in the South China Sea

Author Posting. © Acoustical Society of America, 2013. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 133 (2013): 1306-1319, doi:10.1121/1.4789358.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.The ASIAEX and NLIWI experiments were supported jointly by the National Science Council of Taiwan and the U.S. Office of Naval Research

Comparisons among ten models of acoustic backscattering used in aquatic ecosystem research

Author Posting. © Acoustical Society of America, 2015. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 138 (2015); 3742, doi:10.1121/1.4937607.Analytical and numerical scatteringmodels with accompanying digital representations are used increasingly to predict acoustic backscatter by fish and zooplankton in research and ecosystem monitoring applications. Ten such models were applied to targets with simple geometric shapes and parameterized (e.g., size and material properties) to represent biological organisms such as zooplankton and fish, and their predictions of acoustic backscatter were compared to those from exact or approximate analytical models, i.e., benchmarks. These comparisons were made for a sphere, spherical shell, prolate spheroid, and finite cylinder, each with homogeneous composition. For each shape, four target boundary conditions were considered: rigid-fixed, pressure-release, gas-filled, and weakly scattering. Target strength (dB re 1 m2) was calculated as a function of insonifying frequency (f = 12 to 400 kHz) and angle of incidence (θ = 0° to 90°). In general, the numerical models (i.e., boundary- and finite-element) matched the benchmarks over the full range of simulation parameters. While inherent errors associated with the approximate analytical models were illustrated, so were the advantages as they are computationally efficient and in certain cases, outperformed the numerical models under conditions where the numerical models did not convergeThis work was supported by the NOAA Fisheries Advanced Sampling Technologies Working Group, the Office of Naval Research, and the National Oceanic Partnership Program. Josiah S. Renfree

3D acoustic propagation through an estuarine salt wedge at low-to-mid-frequencies: Modeling and measurement

Author Posting. © Acoustical Society of America, 2019. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 146(3),(2019): 1888-1902, doi:10.1121/1.5125258.The estuarine salt wedge presents a dynamic and highly refractive waveguide, the acoustic propagation characteristics of which are controlled by the water column sound speed gradient and boundary interactions. Acoustically, the salt wedge consists of two isospeed layers separated by a thin, three-dimensional (3D), high-gradient layer. The behavior of a broadband (500–2000 Hz) acoustic field under the influence of an estuarine salt wedge in the Columbia River estuary is explored using two 3D acoustic propagation models: 3D rays and 3D parabolic equation. These model results are compared to data collected during the field experiment. Results demonstrate that the dominant physical mechanism controlling acoustic propagation in this waveguide shifts from 3D bottom scatter in a non-refractive waveguide (before the entrance of the salt wedge) to 3D acoustic refraction with minimal bottom interaction in a refractive waveguide (when the salt wedge occupies the acoustic transect). Vertical and horizontal refraction in the water column and out-of-plane scattering by the bottom are clearly evident at specific narrowband frequencies; however, these mechanisms contribute to, but do not account for, the total observed broadband transmission loss.Environmental input to the acoustic models included high resolution bathymetric survey data provided by Guy Gelfenbaum (USGS), and modeled temperature and salinity profiles of the water column provided by Antonio Baptista, Charles Seaton, and Paul Turner at CMOP. The authors thank Derek Olson (NPS) for invaluable assistance with running the 3DPE model on NPS HPC resources. This work was supported by the Office of Naval Research.2020-03-3