Shelfbreak PRIMER Experiment Research Articles

Geoacoustic parameter estimation using machine learning techniques

The Airy phase region corresponding the minimum group velocity of the dispersive acoustic normal modes in shallow water are extremely sensitive to bottom properties. The group speed minima and the associated frequency data for two lower order modes were used to train a neural network to predict the bottom parameters in a previous study (Potty et al., 2019). The geoacoustic model for the bottom consisted of a sediment layer over acoustic basement. Synthetic data generated by varying the values of the sound speeds in the sediment layer and basement were used to train and evaluate the technique. The output of the neural network was used as the background model for a linear perturbation inversion. Data collected from the Shelf break Primer experiment were used to test the algorithm and the preliminary results were promising. This study will continue the previous work by incorporating higher order modes in the training data, testing with data from other experiments and using other machine learning techniques. The performance of this hybrid approach (neural network combined with linearized inversion) will be compared with fully non-linear inversion, both in terms of accuracy and computation time. [Work supported by the Office of Naval Research.]

Shallow water acoustics and oceanography at the Woods Hole Oceanographic Institution over the last quarter century

Shallow water (coastal) acoustics has been a topic of great interest over quarter century, both from the point of view of learning coastal oceanography and of learning coastal acoustics. Indeed, the two are difficult to separate. In this talk, the research done at the Woods Hole Oceanographic Institution (very often in collaboration with other institutions) over the past 25 years will be discussed, with an emphasis on the major experimental efforts that have been fielded, but also including theoretical and computational efforts. The Barents Sea Polar Front experiment, the Shallow Water Acoustic Random Medium experiment, the Shelfbreak PRIMER experiment, the Asian Seas International Acoustics Experiment, the Shallow Water 2006 experiment, and the Quantifying, Predicting and Exploiting Uncertainty program are some of the at-sea efforts to be discussed. Theoretical advances in shallow water acoustics, as well as computational efforts, such as the Integrated Ocean Dynamics and Acoustics project, will also be ...

Acoustic and sediment data in the southern New England Bight

This study provides a review of the acoustic and ocean bottom sediment data collected during the Shelf Break Primer experiment conducted in 1996. The location of the experiment was in the southern New England Continental Shelf called the “New England Mud Patch.” The mud patch is a 13,000 square kilometer area covered by fine-grained sediment. Previous surveys in this area have estimated the thickness of this fine grained sediment deposit to be as much as 13 m. This layer of sediment rests on a reflector that is geomorphically similar to and continuous with the Holocene transgressive sand sheet, which is exposed on the shelf to the west of this area. This fine-grained sediment layer, which is oriented in an east-west direction seaward of the 55–65 m isobath, contains more than 30% silt and clay. During the Primer experiment, broadband acoustic sources were deployed in the western side of the “mud patch” along and across the continental shelf. The acoustic data collected on a vertical line array will be analyzed. Sediment data from gravity cores from the area will also be presented. [Work sponsored by Office of Naval Research, code 322 OA.]

Experimental design for sediment characterization in the New England Mud Patch

This study focuses on the design of an experiment to estimate the shear wave properties of ocean bottom sediments at a location in the southern New England Continental Shelf called the “New England Mud Patch.” The mud patch is a 13,000 square kilometer area covered by fine-grained sediment. The inversion technique is based on collecting interface wave (Scholte wave) data using geophones on the sea bottom. The data for the inversion consist of Scholte wave phase velocity dispersion calculated from the geophone array data. The present study aims at applying this Scholte wave based shear wave inversion technique to the “mud patch” area. Two different interface wave measurement systems will be presented. Appropriate source to receiver ranges will be explored based on simulations. The engineering challenges associated with deploying the system in a soft seabed will be investigated and design modifications will be investigated. Acoustic and sediment data from the 1996 Shelf Break Primer experiment, which was conducted in the western side of the mud patch, will be reviewed. The simulations will be based on historic sediment and acoustic data. [Work sponsored by Office of Naval Research, code 322 OA.]

Nonlinear optimization for beamforming a geometrically deficient vertical line array: Application to sediment tomography

The 1996 Shelfbreak PRIMER experiment included broadband acoustic transmissions in the vicinity of a shelfbreak front collected using a geometrically deficient vertical line array (VLA). The broadband signals were used to tomographically image sediment sound speed and attenuation. The VLA spanned the lower half of the water column. Hence, the orthonormal properties of the underlying normal modes cannot be guaranteed for any replica vector based on the local modal structure. This produces modal sidelobes in the output of the geometrically deficient VLA. Various methods of extracting the normal modes from VLA data have been developed including a generalized least squares method shown to improve the performance of a geometrically deficient VLA processing phase encoded tomography signals [Chiu et al., IEEE J. Ocean. Eng. 22, 522–533 (2005)]. The present study seeks to enhance the modal resolution for the reception of high-amplitude, impulsive signals transmitted over a wide variety of source receiver paths in shallow water where ensemble averaging is not an option. The method uses nonlinear optimization techniques to compute a set of array element coefficients that enhance suppression of modal sidelobes, while maintaining adequate spatial matching with the desired mode. [Work supported by Office of Naval Research.]

Propagation of impulsive broadband signals in a coastal ocean setting during the 1996 Shelfbreak Primer experiment

The 1996 Shelfbreak PRIMER experiment provided an opportunity to study the impulse response of a coastal ocean waveguide using broadband acoustic signals from explosive sources. Acoustic transmission paths in the vicinity of the shelfbreak included various orientations ranging from up‐slope to along‐slope, including interactions with a shelfbreak front. Acoustic receptions were acquired with a 16‐element vertical line array (VLA). In addition, thermistor string data acquired at the receiving array suggest that a group of high‐amplitude, internal waves traversed the test site during this portion of the experiment. Modal decomposition of broadband signal arrivals was performed to investigate variation of the impulse response during source deployments. Variations in the received spectra of individual normal modes were compared with numerical predictions for impulsive broadband signals propagating in range‐dependent environments constructed using oceanographic data available for the test site. The potential for mode coupling and three‐dimensional effects to shape the modal and spectral distribution of received energy is being investigated. Numerical and experimental results will be discussed. [Work supported by Office of Naval Research.]

Climatological Estimation of Environmental Uncertainty Over the Middle Atlantic Bight Shelf and Slope

Historical hydrographic data are used to determine the spatial and seasonal patterns of uncertainty in thermohaline and sound-speed fields in a well-sampled region, the continental shelf and slope in the Middle Atlantic Bight (MAB). Several different historical databases are combined to produce two-dimensional (2-D) plan view and cross-shelf fields of temperature, salinity, and sound speed in two separate regions, the New England shelf and the shelf off Delaware and Maryland. In addition, spatial maps of the sound-speed fields reveal that the maximum variance of the sound speed occurs at the edge of the continental shelf, in the vicinity of the shelfbreak front. The standard deviation of the sound speed was largest during the spring and summer, with magnitudes as large as 14 m/s in a narrow band coinciding with the mean position of the shelfbreak front. During spring the peak in variance was located near the surface outcrop of the front, but during summer the maximum variance was centered at a depth of 30 m, immediately beneath the seasonal thermocline. Comparisons with both synoptic measurements from the Shelfbreak PRIMER experiment as well as moored time series from the Nantucket Shoals Flux Experiment confirm that the shelfbreak front is a “hotspot” of uncertainty (maximum variance), and that the vertical structure of the peak variance is dependent on the presence or absence of the seasonal thermocline.

Oceanographic and Sound Speed Fields for the ESME Workbench

The authors describe the effort to provide three-dimensional global thermohaline and sound speed fields for use in the effects of sound in the marine environment (ESME) workbench suite of programs. The primary fields used are from the modular ocean data assimilation system (MODAS), developed by Fox et al. The system provides global thermohaline and sound speed fields on a daily basis using environmental inputs from the U.S. Navy as well as remote sensing of sea surface temperature and sea surface height. To examine the MODAS fields, the authors also used data from the Southern California Bight collected by the California Cooperative Fisheries Investigations as well as high-resolution hydrographic data collected over the continental shelf south of New England as part of the shelfbreak PRIMER experiment. MODAS performs well for features such as large-scale boundary currents and eddies but is more limited in resolving features such as shelfbreak and coastal fronts, which have small spatial and temporal correlation scales. Because of the considerable computational needs of other ESME modules and its use as a planning tool, the authors present a pragmatic approach for future applications

A large‐amplitude meander of the shelfbreak front during summer south of New England: Observations from the Shelfbreak PRIMER experiment

In order to examine spatial and temporal variability of the shelfbreak front during peak stratification, repeated surveys using a towed undulating vehicle (SeaSoar) are used to describe the evolution of shelfbreak frontal structure during 26 July to 1 August 1996 south of New England. Spatial correlation (e‐folding) scales for the upper 60 m of the water column were generally between 8 and 15 km for temperature, salinity, and velocity. Temporal correlation scales were about 1 day. The frontal variability was dominated by the passage of a westward propagating meander that had a wavelength of 40 km, a propagation speed of 0.11 m s−1, and an amplitude of 15 km (30 km from crest to trough). Along‐front geostrophic velocities (referenced to a shipboard acoustic Doppler current profilers) were as large as 0.45 m s−1, although subject to significant along‐front variations. The relative vorticity within the jet was large, with a maximum 0.6 of the local value of the Coriolis parameter. Seaward of the front, a small detached eddy consisting of shelf water was present with a diameter of approximately 15 km. Ageostrophic contributions to the velocity field are estimated to be as large as 0.3 m s−1 in regions of sharp curvature within the meander. These observations strongly suggest that during at least some time periods, shelfbreak exchange is nonlinear (large Rossby number) and dominated by features on a horizontal scale of order 10 km.

Inversion for sediment geoacoustic properties at the New England Bight

This article discusses inversions for bottom geoacoustic properties using broadband acoustic signals obtained from explosive sources. Two different inversion schemes for estimating the compressional wave speeds and attenuation are presented in this paper. In addition to these sediment parameters, source-receiver range is also estimated using the arrival time data. The experimental data used for the inversions are SUS charge explosions acquired on a vertical hydrophone array during the Shelf Break Primer Experiment conducted south of New England in the Middle Atlantic Bight in August 1996. The modal arrival times are extracted using a wavelet analysis. In the first inversion scheme, arrival times corresponding to various modes and frequencies from 10 to 200 Hz are used for the inversion of compressional wave speeds. A hybrid inversion scheme based on a genetic algorithm (GA) is used for the inversion. In an earlier study, Potty et al. [J. Acoust. Soc. Am. 108(3), 973-986 (2000)] have used this hybrid scheme in a range-independent environment. In the present study results of range-dependent inversions are presented. The sound speeds in the water column and bathymetry are assumed range dependent, whereas the sediment compressional wave speeds are assumed range independent. The variations in the sound speeds in the water column are represented using empirical orthogonal functions (EOFs). The replica fields corresponding to the unknown parameters were constructed using adiabatic theory. In the second inversion scheme, modal attenuation coefficients are calculated using modal amplitude ratios. The ratios of the modal amplitudes are also calculated using time-frequency diagrams. A GA-based inversion scheme is used for this search. Finally, as a cross check, the computed compressional wave speeds along with the modal arrival times were used to estimate the source-receiver range. The inverted sediment properties and ranges are seen to compare well with in situ measurements and historical data.

Characteristics of acoustic propagation to the eastern vertical line array receiver during the summer 1996 New England shelfbreak PRIMER experiment

During July and August of 1996, the summer component of the New England shelfbreak front PRIMER experiment was fielded in the Mid-Atlantic Bight, at a site due south of Martha's Vineyard, MA. This study produced acoustic transmission data from a network of moored sources and receivers in conjunction with very-high-resolution oceanography measurements. This paper analyzes receptions at the northeast array receiver from two 400 Hz acoustic tomography sources, with the transmission paths going from the continental slope onto the continental shelf. These data, along with forward acoustic-propagation modeling based on moored oceanographic data, SeaSoar hydrography measurements, and bottom measurements, reveal many new and interesting aspects of acoustic propagation in a complicated slope-shelf environment. For example, one sees that both the shelfbreak front and tidally generated soliton internal wave packets produce stronger mode coupling than previously expected, leading to an interesting time-and-range-variable population of the acoustic normal modes. Additionally, the arrival time wander and the signal spread of acoustic pulses show variability that can be attributed to the presence of a frontal meander and variability in the soliton field. These and other effects are discussed in this paper, with an emphasis on creating a strong connection between the environmental measurements and the acoustic field characteristics.

Directional noise and correlation of signal and noise variability in the ASIAEX South China Sea Experiment

As part of the 2001 ASIAEX South China Sea experiment, known acoustic signals and noise were recorded for 16 days with co-located horizontal and vertical receiving arrays in 120-m depth water at the edge of the continental shelf. The location was south of China and southwest of Taiwan. Vertical and horizontal directionality of both signals and noise can be estimated using the two arrays. Directionality can be linked to vertical mode bandwidth. Furthermore, because of mode stripping effects, it can indicate the amount of mode coupling in the vicinity of the receiver. Previously, arrival time and total energy of the signals have been shown to respond to the strong nonlinear internal waves and internal tides of the area. Here, we investigate the response of noise energy and directionality to the waves, and compare with the response of signal energy and directionality. The results can be compared to the Shelfbreak PRIMER experiment in the Mid-Atlantic Bight, where signal and noise parameters recorded with a VLA were correlated. Correlation of signal and noise violates assumptions used in many signal processing algorithms.

Spatial and temporal variations in acoustic propagation characteristics at the new england shelfbreak front

The spatial and temporal variability of the acoustic field in the region of a strong coastal shelfbreak front are examined, using the high-resolution environmental data from the 1996-1997 New England shelfbreak PRIMER experiment to provide input to acoustic propagation models. Specifically, the "SeaSoar" undulating conductivity-temperature-depth (CTD) probe across-shelf transects provide 1-km along-track resolution, including the front, during the spring, summer, and winter seasons. These data allow one to study the diurnal and seasonal temporal variation of the acoustic field, as well as the varying spatial structure of the field. Using the RAM parabolic equation code, across-shelf acoustic field structure at 200, 400, and 1000 Hz is studied for various source depths. A number of interesting propagation effects are noted, the most interesting of which are the inhibition of strong acoustic-bottom interaction by the warm shelf water beneath the shelfbreak front and the existence of small-scale ducts near the front, due to offshore transport. Data from the vertical line arrays deployed as part of PRIMER offer partial validation of the predictions made. Specifically, it is seen that the mean received levels are in reasonable accord with propagation calculations made using locally measured bottom properties and the SeaSoar water-column measurements.

Long range sediment tomography

The development of long range sediment tomography using shot data and its application in various field experiments is presented. Whereas traditional ocean acoustic tomography has mainly relied on linear inverse theory using the travel time of rays in deep water, our technique relies on nonlinear optimization techniques using the frequency-dependent travel time of normal modes in shallow water. Our experience with broadband sediment tomography using explosive sources started with the Barents Sea Polar Front Experiment where sediment properties were extracted using ground wave analysis. The techniques were further refined during the Shelf Break Primer Experiment in the New England Bight where a nonlinear inversion scheme using the Genetic Algorithm was successfully applied. The inversion scheme was based on modal travel time dispersion characteristics, which in shallow water conditions, is highly sensitive to the bottom properties. Advanced signal processing tools for the space–time–frequency processing and hybrid optimizaton techniques for global search were developed and implemented in parallel. In addition to the individual modal arrival times, emphasis has now been placed on the arrival corresponding to the Airy phase. These inversion techniques are currently being applied to the data from ASIAEX-East China Sea Experiment. Characteristics of this tomography approach such as spatial coverage, resolution, error bars, robustness, and simple instrumentation requirements will be presented. The usefulness of this inversion approach as a rapid environmental assessment tool will be highlighted. [Work supported by ONR.]

Observations and modeling of acoustic intensity fluctuations seen during the 1996 summer New England shelfbreak PRIMER experiment

In this paper we discuss the intensity fluctuation characteristics of 400-Hz acoustic transmissions made in the Mid-Atlantic Bight during the summer of 1996. The transmissions traversed variable topography, the dynamic shelfbreak front, and strong nonlinear internal waves, all of which affected the acoustic propagation. In studying the intensity fluctuations, we look both at data from the PRIMER vertical line array receiver and at output from a broadband parabolic equation model intended to simulate the experimental conditions with high fidelity. The statistics of the fluctuations, the physical causes of the fluctuations, and the correlation with the oceanographic forcing in different frequency bands (subtidal, tidal, and high frequency) all are examined. [Work supported by ONR.]

Observations of intensity fluctuations during the summer New England shelf break Primer study

We present intensity fluctuation statistics of point-to-point transmission data taken during the summer shelfbreak Primer experiment. We focus on broadband 400 Hz transmissions from two bottom mounted sources on the continental slope to a vertical line array on the shelf, at distances of 60 and 42 km. The data were collected over 11 days in late July and early August of 1996. Single phone, time averaged, and time and depth average intensity statistics are examined. Both tracks showed a strong M2 tidal effect on intensity, as well as mesoscale induced variations. [Work supported by ONR.]

Tomographic inversion for sediment parameters in shallow water

This article discusses inversions for bottom geoacoustic properties using broadband acoustic signals obtained from explosive sources. The experimental data used for the inversions are SUS charge explosions acquired on a vertical hydrophone array during the Shelf Break Primer Experiment conducted south of New England in the Middle Atlantic Bight in August 1996. The SUS signals were analyzed for their time-frequency behavior using wavelets. The group speed dispersion curves were obtained from the wavelet scalogram of the SUS signals. A genetic algorithm (GA) was used for the inversion of sound speeds in the water column and compressional wave speeds in the sediment layers. The variations in the sound speeds in the water column were represented using empirical orthogonal functions (EOFs). A range-independent normal mode routine was used to construct the replica fields corresponding to the parameters. Comparison of group speeds for modes 1 to 9 and for a range of frequencies 8 to 200 Hz was used to arrive at the best parameter fit. An efficient hybrid optimization scheme using the GA and a Levenberg-Marquardt algorithm is presented. Linear perturbation methods were also used to "fine tune" the inversions and to obtain resolution and variance estimates. Analysis was also done to compute the degree of convergence of each of the parameters by explicitly calculating the Hessian matrices numerically. A posteriori estimation of mean and covariance was also done to obtain error estimates. Group speeds for the inverted sound speed fields provide an excellent match to the experimental data. The inverted sediment compressional speed profile compares well with in situ measurements.

Geoacoustic Tomography Range Dependent Inversions on a Single Slice

Journal of Computational AcousticsVol. 08, No. 02, pp. 325-345 (2000) No AccessGEOACOUSTIC TOMOGRAPHY: RANGE DEPENDENT INVERSIONS ON A SINGLE SLICEGOPU R. POTTY and JAMES H. MILLERGOPU R. POTTYDepartment of Ocean Engineering, University of Rhode Island, Narragansett, RI 02882, USA Search for more papers by this author and JAMES H. MILLERDepartment of Ocean Engineering, University of Rhode Island, Narragansett, RI 02882, USA Search for more papers by this author https://doi.org/10.1142/S0218396X00000339Cited by:5 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail AbstractA hybrid inversion scheme is used for the inversion of bottom geoacoustic properties using synthetic data as well as broadband signals from explosive sources. This technique is shown to be effective for range dependent inversion on a single slice using synthetic and experimental data. The experimental data was acquired during the Shelf Break Primer Experiment. Time-frequency analysis was performed using wavelets. Group speeds obtained from the time-frequency scalograms were used as data for the inversion. The hybrid method consists of a Genetic Algorithm, which performs the global search, and a Levenberg-Marquardt method, which hastens the descent to the global minimum. Error estimates based on Hessians and a posteriori variances are also provided. Resolution is estimated using an a posteriori analysis. FiguresReferencesRelatedDetailsCited By 5Acoustic signal characterization based on hidden Markov models with applications to geoacoustic inversionsCostas Smaragdakis and Michael I. Taroudakis1 Oct 2020 | The Journal of the Acoustical Society of America, Vol. 148, No. 4Statistical Characterization of Acoustic Signals Using 1D Wavelet Transforms with Applications in Acoustical OceanographyMichael I. Taroudakis19 December 2018 | Journal of Theoretical and Computational Acoustics, Vol. 26, No. 04An Equivalent Transform Method for Evaluating the Effect of Water-Column Mismatch on Geoacoustic InversionY.-T. Lin, C.-F. Chen and J.F. Lynch1 Apr 2006 | IEEE Journal of Oceanic Engineering, Vol. 31, No. 2Classification of shallow-water acoustic signals via alpha-Stable modeling of the one-dimensional wavelet coefficientsMichael I. Taroudakis, George Tzagkarakis and Panagiotis Tsakalides1 Mar 2006 | The Journal of the Acoustical Society of America, Vol. 119, No. 3ON THE USE OF THE REASSIGNED WAVELET TRANSFORM FOR MODE IDENTIFICATIONMICHAEL I. TAROUDAKIS and GEORGE TZAGKARAKIS21 November 2011 | Journal of Computational Acoustics, Vol. 12, No. 02 Recommended Vol. 08, No. 02 Metrics History Received 24 June 1999 Revised 21 February 2000 PDF download

GEOACOUSTIC TOMOGRAPHY: RANGE DEPENDENT INVERSIONS ON A SINGLE SLICE

A hybrid inversion scheme is used for the inversion of bottom geoacoustic properties using synthetic data as well as broadband signals from explosive sources. This technique is shown to be effective for range dependent inversion on a single slice using synthetic and experimental data. The experimental data was acquired during the Shelf Break Primer Experiment. Time-frequency analysis was performed using wavelets. Group speeds obtained from the time-frequency scalograms were used as data for the inversion. The hybrid method consists of a Genetic Algorithm, which performs the global search, and a Levenberg-Marquardt method, which hastens the descent to the global minimum. Error estimates based on Hessians and a posteriori variances are also provided. Resolution is estimated using an a posteriori analysis.

Inversion of sediment parameters in a shallow-water range-dependent environment

The propagation of acoustic energy in a range dependent environment will be analyzed. The broadband acoustic signals from explosive sources collected during the Shelf Break PRIMER Experiment will be used for this study. Time–frequency behavior of these signals will be analyzed using wavelets. Upslope propagation along varying bathymetry (from 800 m at source location to 90 m at the receiver) and sound speed is considered. A simple model for the sediment compressional speeds will be extracted using a hybrid inversion scheme. This hybrid scheme uses a genetic algorithm and Levenberg–Marquardt nonlinear least-squares method. Inversion is based on group speed dispersion. Theoretical group speeds will be calculated based on range-dependent propagation. [Work supported by ONR.]