The long-term goal of the research is to increase the physical understanding of acoustic propagat... more The long-term goal of the research is to increase the physical understanding of acoustic propagation in continental shelf and slope environments in the 25-5000 Hz band. This includes both the physics of the seabed and the coupling to physical mechanisms in the water column in complex range-and azimuth-dependent littoral waveguides. OBJECTIVES There were two main objectives of the current research. The first objective was to complete a final numerical implementation of a statistical inference approach based on a maximum entropy formalism. The second objective was to combine the waveguide parameter statistical inferences with geophysical data from the Shallow Water 2006 (SW06) experiment on the New Jersey continental shelf to model range-dependent acoustic data for the purpose of determining the bandwidth and range over which the effects of range-dependent inhomogenities in the sub bottom layering can be discerned. APPROACH The approach applied in this work was to continue to use data obtained from the SW06 experiment to test hypotheses made for statistical inference of waveguide parameters and the effects of sub bottom seabed layering on low frequency acoustic propagation. Further, there is ongoing collaboration between Mr. Jason Sagers, my graduate student, and I on (1) identifying mode coupling effects in SW06 data and (2) performing statistical inference in environments with significant horizontal variability. The theoretical approach to statistical inference is based on maximum entropy. The main advancement made by the current work is the discovery of how to specify the average error constraint for maximization of the Shannon entropy. 1 Previously, all statistical inference methods in ocean DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.
Public reporting burden for the collection of information is estimated to average 1 hour per resp... more Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.
Abstract : Viewgraphs from a progress report on the estimation of geoacoustic parameters from mea... more Abstract : Viewgraphs from a progress report on the estimation of geoacoustic parameters from measured time series taken during the East China Sea component of ASIAEX.
The Shallow Water 2006 ocean acoustics experiment on the New Jersey continental shelf was designe... more The Shallow Water 2006 ocean acoustics experiment on the New Jersey continental shelf was designed in part to determine the frequency dependence of sound speed and attenuation for a sandy sediment in the 50-3000 Hz band. Two acoustic arrays in L-geometries were positioned about 25 km apart on a ridge of coarse sand. Segments of narrowband and impulsive acoustic data were analyzed for the information they contain on the seabed geoacoustic structure and the frequency dependence of the top sediment layer attenuation. The results clearly demonstrate a nonlinear frequency dependence of the absorption.
The Journal of the Acoustical Society of America, 2008
Acoustic measurements were made on a sand ridge on the New Jersey continental shelf. Data collect... more Acoustic measurements were made on a sand ridge on the New Jersey continental shelf. Data collected on two L arrays separated by 20 km from a single multi-frequency tow suggest small horizontal environmental variability. Values for the sound speed structure of the seabed are extracted by first applying a geo-acoustic inversion method to broadband and narrowband acoustic data from short-range sources. Then, a parabolic equation algorithm is used to properly include the bathymetry and sub-bottom layering. Finally, the frequency dependence of the seabed attenuation is inferred by optimizing the model fit to long-range transmission loss data in the 50-3000 Hz band.
The Journal of the Acoustical Society of America, 1983
This facilitates the modeling of acoustic scattering from a rough surface. The method may be appl... more This facilitates the modeling of acoustic scattering from a rough surface. The method may be applied to describe scattering within a waveguide with a rough surface, or to model energy losses due to scattering out of a surface duct. Numerical procedures have been codified to solve the equations resulting from the analysis and some examples are provided. 1:13 W3. Sound field fluctuation in shallow water waveguide. C. S. Clay, Y.
The Journal of the Acoustical Society of America, 2003
A broadband model of seabed reverberation in a shallow water waveguide is used to analyze data me... more A broadband model of seabed reverberation in a shallow water waveguide is used to analyze data measured in the Area Characterization Test I (ACT I). Given a source spectrum, a mean geoacoustic profile for the waveguide, and statistics characterizing the scattering sources (including fluctuations in seabed sound speed and density as well as seabed interface roughness) the model simulates time series measured in a monostatic geometry. It accomplishes this by solving the integral form of the Helmholtz equation in a random medium in the Born (or single scattering) approximation using the ORCA normal mode model to compute the unperturbed Green’s functions. Statistics of the scattering sources are inferred from comparisons between modeled time series and experimental data. Also, the effects of uncertainties in the source spectrum are considered, and the validity of the Born approximation in this context is discussed. [Work supported by ONR.]
The Journal of the Acoustical Society of America, 2009
The debate on the sound speed dispersion and the frequency dependence of sound attenuation in sea... more The debate on the sound speed dispersion and the frequency dependence of sound attenuation in seabottoms has persisted for decades, mainly due to the lack of sufficient experimental data in the low-frequency ͑LF͒ to high-frequency speed/attenuation transition band. This paper analyzes and summarizes a set of LF measurements in shallow water that have resulted in the identification of nonlinear frequency dependence of sound attenuation in the effective media of sandy seabottoms. The long-range acoustic measurements were conducted at 20 locations in different coastal zones around the world. The seabed attenuations, inverted from different acoustic field measurements and characteristics, exhibit similar magnitude and nonlinear frequency dependence below 1000 Hz. The resulting effective sound attenuation can be expressed by ␣͑dB/ m͒ = ͑0.37 Ϯ 0.01͒͑f / 1000͒ ͑1.80Ϯ0.02͒ for 50-1000 Hz. The corresponding average sound speed ratio at the bottom-water interface in the 50-600 Hz range is 1.061Ϯ 0.009. Both the LF-field-derived sound speed and attenuation can be well described by the Biot-Stoll model with parameters that are consistent with either theoretical considerations or experimental measurements. A combination of the LF-field-inverted data with the SAX99, SAX04, and other high-frequency measurements offers a reference broadband data set in the 50-400 000 Hz range for sonar prediction and sediment acoustics modeling.
The Journal of the Acoustical Society of America, 2003
A methodology for simultaneous inversion for source levels, source track parameters, and environm... more A methodology for simultaneous inversion for source levels, source track parameters, and environmental parameters is described. An application to acoustic data recorded on a bottom-mounted, horizontal line array at a soft-sediment, shallow-water site in the Gulf of Mexico off Port Aransas, TX is discussed. This inversion approach may be viewed as a technique for making TL measurements with sources of opportunity by a generalization of the inversion of measured TL as a function of range for geoacoustic parameters for which the source depth is known. The technique involves minimizing a cost function formed from a sum over hydrophones and frequencies of the squared difference between received levels and modeled intensities. The inversion methodology will be validated using known cw tones emitted by a towed source and demonstrated for sources of opportunity using acoustic emissions from the RV LONGHORN, the experimental platform for the experiment. [Work supported by ONR.]
The Journal of the Acoustical Society of America, 2003
The inversion of range-dependent broadband data in shallow water is presented using a previously ... more The inversion of range-dependent broadband data in shallow water is presented using a previously developed approach with rays and complex bottom plane-wave reflection coefficients [Stotts, J. Acoust. Soc. Am. 109, 2334 (2001)], allowing separation of seabed physics from water column contributions. Using geometrical optics, waterborne eigenray characteristics are calculated once and stored. Model fields are calculated by including reflection coefficient contributions from each bottom interaction and are evaluated for each perturbation of the seabed properties using simulated annealing to minimize a Bartlett-type cost function. Inversion results from range-independent and -dependent data taken during recent experiments off the coast of Florida are presented using a two-layer model. Implosive source broadband data and XBTs were recorded out to 10 km from a bottom-mounted, 52-element array 229-m deep. Grab samples obtained during the experiment show a thin, hard, crusted surface sediment. Inversions reveal an underlying softer sediment. Model time series using one inverted parameter set are compared to the data obtained from sources at different ranges. Data arrivals are compared to eigenray arrivals providing further propagation insight. Consistent inversion results from other forward models are discussed.
The Journal of the Acoustical Society of America, 2002
Time series data collected on the APL-UW/URI VLA in the East China Sea as part of the Asian Sea I... more Time series data collected on the APL-UW/URI VLA in the East China Sea as part of the Asian Sea International Acoustics Experiment are analyzed for the information they contain on the characteristics of the seabed. Sound generated by explosive sources deployed by the IOA propagates in a shallow water wave guide under downward refracting conditions, making the received field at
The Journal of the Acoustical Society of America, 2002
Low‐frequency monostatic reverberation data collected in the East China Sea on a VLA are analyzed... more Low‐frequency monostatic reverberation data collected in the East China Sea on a VLA are analyzed to infer bottom scattering strength characteristics. The VLA was deployed and the data collected by researchers from the Institute of Ocean Acoustics, Beijing, China. Reverberation data originating from ranges from 3–15 km are analyzed using coherent array processing methods to determine scattering strengths as a function of frequency and angle at the scatterer. Subaperture processing is used to separate sea surface and bottom contributions and to gain physical insight into the scattering mechanisms responsible for the observed reverberation level. Modeled transmission loss obtained from analyses of measured forward propagation data is employed within the framework of the subaperture signal processing to enable the extraction of the scattering strength. [Work supported by ONR.]
The Journal of the Acoustical Society of America, 2002
Near a shoreline an acoustic waveguide can be modeled by a wedge-shaped geometry with a penetrabl... more Near a shoreline an acoustic waveguide can be modeled by a wedge-shaped geometry with a penetrable bottom. The propagation of sound in such a waveguide was studied in a tank experiment conducted by Tindle et al. [J. Acoust. Soc. Am. 81, 275-286 (1987); 81, 287-294 (1987)]. An analysis of the time series data measured in this experiment was carried out by Royal et al. (unpublished), in which time series were simulated using a broadband, one-way, coupled normal mode approach. This analysis is extended using a two-way propagation approach that solves the integral equation form of the coupled mode equation. Also, the modal continuum is treated more realistically through the employment of a leaky mode decomposition. In particular, the importance of backscattering and coupling to the continuum is gauged by comparing the experimental data with the results of the two approaches.
The Journal of the Acoustical Society of America, 2008
On the New Jersey continental shelf ambient sound levels were recorded during tropical storm Erne... more On the New Jersey continental shelf ambient sound levels were recorded during tropical storm Ernesto that produced wind speeds up to 40 knots in early September 2006. The seabed at the position of the acoustic measurements can be approximately described as coarse sand. Differences between the ambient noise levels for the New Jersey shelf measurements and deep water reference measurements are modeled using both normal mode and ray methods. The analysis is consistent with a nonlinear frequency dependent seabed attenuation for the New Jersey site.
The Journal of the Acoustical Society of America, 2008
ABSTRACT The ambient noise level variations produced by Hurricane Ernesto were observed by the SW... more ABSTRACT The ambient noise level variations produced by Hurricane Ernesto were observed by the SWAMI32, SWAMI52 and SHARK arrays as the storm passed over the SW06 shallow water site. Microseism signals were detected in the water column near 0.1 Hz and were tracked with a beamformer over a period of several days observing variations that were very closely linked to measured surface waves. 5-75 Hz beamforming showed a sound-field dominated by local surface-noise punctuated by brief surges of noise from distant sources. Beamforming and time-domain cross-correlations showed that changes in acoustic environment on the time-scale of hours occurred at all three arrays with good correlation in time and directionality suggesting the storm induced noise-field is homogeneous over many kilometers.
The Journal of the Acoustical Society of America, 2008
Full-field inversion methods over large frequency bands and spatial scales attempt to exploit the... more Full-field inversion methods over large frequency bands and spatial scales attempt to exploit the sensitivity of the frequency and spatial dependence of the acoustic field of the properties to the seabed. A comprehensive set of broadband impulsive and narrowband tonal acoustic recordings in the 5-3000 Hz band from two Larrays separated by 20 km were made in a shallow water area on the New Jersey continental shelf during the Shallow Water 2006 (SW06) experiment. In addition, surface ship of opportunity passages on both arrays were recorded along with noise during the passage of tropical storm Ernesto. Reverberation and transmission loss data in the 25-9200 Hz band from explosive sources were also collected at a nearby site prior to the SW06 experiment. Numerous full-field geo-acoustic inversion methods and analyses of all these acoustic data with supporting range and azimuth-dependent geo-physical measurements are employed to characterize the seabed properties. For example, the analyses of these data permit inferences about the frequency-dependence of the seabed sound speed and attenuation to be made. The overlapping data types act to reduce the intrinsic ambiguities associated with inversion, quantify the spatial variability, and serve as independent validation.
The Journal of the Acoustical Society of America, 1996
A theoretical analysis of pressure time series generated by small explosive sources and recorded ... more A theoretical analysis of pressure time series generated by small explosive sources and recorded on both an HLA and a VLA deployed in the Hudson canyon region off the New Jersey coast near the AMCOR 6010 borehole is presented. The SVP in the water column has an isovelocity layer down to a depth of about 20 m followed by a strong negative gradient to about 45 m where the profile becomes approximately isovelocity to theseafloor at 73 m. This sound‐speed structure creates a unique time series structure on the VLA as a function of source range. The data are simulated with a broadband normal mode‐ approach recently discussed in the literature [J. Acoust. Soc. Am. 98, 1682–1698 (1995); IEEE J. Ocean. Eng. 21 (1) (1996)]. The representation of the spatial and temporal structure of the time series in terms of a modal structure reveals several unique aspects of the structure of the SVP in the water column and the geoacoustic structure of the bottom. The details of the modal structure of the sound field clearly def...
The Journal of the Acoustical Society of America, 1993
Data from a moving source received by three horizontally separated bottomed sensors in a shallow‐... more Data from a moving source received by three horizontally separated bottomed sensors in a shallow‐water environment are analyzed using a broadband matched‐field approach to source localization. The water depth was approximately 120 m, and the low bottom loss in the area results in low spatial coherence of the broadband field. The modeled acoustic fields are constructed via a ray model with wave‐like corrections. Localizations are made in the x‐y plane. The time evolution of the matched‐field surfaces produced from the data agree well with simulated surfaces. Matched‐field surfaces are generated successively in intervals of about 1.6 s in small search areas with a fine spatial grid to test the possibility of tracking a source. Results of the source tracking will be presented. The analysis also considers the effects of the sea floor and environmental mismatch of sea floor descriptions on localization in the context of spatial coherence. In addition the effect of varying the receiver separation on the ability...
The long-term goal of the research is to increase the physical understanding of acoustic propagat... more The long-term goal of the research is to increase the physical understanding of acoustic propagation in continental shelf and slope environments in the 25-5000 Hz band. This includes both the physics of the seabed and the coupling to physical mechanisms in the water column in complex range-and azimuth-dependent littoral waveguides. OBJECTIVES There were two main objectives of the current research. The first objective was to complete a final numerical implementation of a statistical inference approach based on a maximum entropy formalism. The second objective was to combine the waveguide parameter statistical inferences with geophysical data from the Shallow Water 2006 (SW06) experiment on the New Jersey continental shelf to model range-dependent acoustic data for the purpose of determining the bandwidth and range over which the effects of range-dependent inhomogenities in the sub bottom layering can be discerned. APPROACH The approach applied in this work was to continue to use data obtained from the SW06 experiment to test hypotheses made for statistical inference of waveguide parameters and the effects of sub bottom seabed layering on low frequency acoustic propagation. Further, there is ongoing collaboration between Mr. Jason Sagers, my graduate student, and I on (1) identifying mode coupling effects in SW06 data and (2) performing statistical inference in environments with significant horizontal variability. The theoretical approach to statistical inference is based on maximum entropy. The main advancement made by the current work is the discovery of how to specify the average error constraint for maximization of the Shannon entropy. 1 Previously, all statistical inference methods in ocean DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.
Public reporting burden for the collection of information is estimated to average 1 hour per resp... more Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.
Abstract : Viewgraphs from a progress report on the estimation of geoacoustic parameters from mea... more Abstract : Viewgraphs from a progress report on the estimation of geoacoustic parameters from measured time series taken during the East China Sea component of ASIAEX.
The Shallow Water 2006 ocean acoustics experiment on the New Jersey continental shelf was designe... more The Shallow Water 2006 ocean acoustics experiment on the New Jersey continental shelf was designed in part to determine the frequency dependence of sound speed and attenuation for a sandy sediment in the 50-3000 Hz band. Two acoustic arrays in L-geometries were positioned about 25 km apart on a ridge of coarse sand. Segments of narrowband and impulsive acoustic data were analyzed for the information they contain on the seabed geoacoustic structure and the frequency dependence of the top sediment layer attenuation. The results clearly demonstrate a nonlinear frequency dependence of the absorption.
The Journal of the Acoustical Society of America, 2008
Acoustic measurements were made on a sand ridge on the New Jersey continental shelf. Data collect... more Acoustic measurements were made on a sand ridge on the New Jersey continental shelf. Data collected on two L arrays separated by 20 km from a single multi-frequency tow suggest small horizontal environmental variability. Values for the sound speed structure of the seabed are extracted by first applying a geo-acoustic inversion method to broadband and narrowband acoustic data from short-range sources. Then, a parabolic equation algorithm is used to properly include the bathymetry and sub-bottom layering. Finally, the frequency dependence of the seabed attenuation is inferred by optimizing the model fit to long-range transmission loss data in the 50-3000 Hz band.
The Journal of the Acoustical Society of America, 1983
This facilitates the modeling of acoustic scattering from a rough surface. The method may be appl... more This facilitates the modeling of acoustic scattering from a rough surface. The method may be applied to describe scattering within a waveguide with a rough surface, or to model energy losses due to scattering out of a surface duct. Numerical procedures have been codified to solve the equations resulting from the analysis and some examples are provided. 1:13 W3. Sound field fluctuation in shallow water waveguide. C. S. Clay, Y.
The Journal of the Acoustical Society of America, 2003
A broadband model of seabed reverberation in a shallow water waveguide is used to analyze data me... more A broadband model of seabed reverberation in a shallow water waveguide is used to analyze data measured in the Area Characterization Test I (ACT I). Given a source spectrum, a mean geoacoustic profile for the waveguide, and statistics characterizing the scattering sources (including fluctuations in seabed sound speed and density as well as seabed interface roughness) the model simulates time series measured in a monostatic geometry. It accomplishes this by solving the integral form of the Helmholtz equation in a random medium in the Born (or single scattering) approximation using the ORCA normal mode model to compute the unperturbed Green’s functions. Statistics of the scattering sources are inferred from comparisons between modeled time series and experimental data. Also, the effects of uncertainties in the source spectrum are considered, and the validity of the Born approximation in this context is discussed. [Work supported by ONR.]
The Journal of the Acoustical Society of America, 2009
The debate on the sound speed dispersion and the frequency dependence of sound attenuation in sea... more The debate on the sound speed dispersion and the frequency dependence of sound attenuation in seabottoms has persisted for decades, mainly due to the lack of sufficient experimental data in the low-frequency ͑LF͒ to high-frequency speed/attenuation transition band. This paper analyzes and summarizes a set of LF measurements in shallow water that have resulted in the identification of nonlinear frequency dependence of sound attenuation in the effective media of sandy seabottoms. The long-range acoustic measurements were conducted at 20 locations in different coastal zones around the world. The seabed attenuations, inverted from different acoustic field measurements and characteristics, exhibit similar magnitude and nonlinear frequency dependence below 1000 Hz. The resulting effective sound attenuation can be expressed by ␣͑dB/ m͒ = ͑0.37 Ϯ 0.01͒͑f / 1000͒ ͑1.80Ϯ0.02͒ for 50-1000 Hz. The corresponding average sound speed ratio at the bottom-water interface in the 50-600 Hz range is 1.061Ϯ 0.009. Both the LF-field-derived sound speed and attenuation can be well described by the Biot-Stoll model with parameters that are consistent with either theoretical considerations or experimental measurements. A combination of the LF-field-inverted data with the SAX99, SAX04, and other high-frequency measurements offers a reference broadband data set in the 50-400 000 Hz range for sonar prediction and sediment acoustics modeling.
The Journal of the Acoustical Society of America, 2003
A methodology for simultaneous inversion for source levels, source track parameters, and environm... more A methodology for simultaneous inversion for source levels, source track parameters, and environmental parameters is described. An application to acoustic data recorded on a bottom-mounted, horizontal line array at a soft-sediment, shallow-water site in the Gulf of Mexico off Port Aransas, TX is discussed. This inversion approach may be viewed as a technique for making TL measurements with sources of opportunity by a generalization of the inversion of measured TL as a function of range for geoacoustic parameters for which the source depth is known. The technique involves minimizing a cost function formed from a sum over hydrophones and frequencies of the squared difference between received levels and modeled intensities. The inversion methodology will be validated using known cw tones emitted by a towed source and demonstrated for sources of opportunity using acoustic emissions from the RV LONGHORN, the experimental platform for the experiment. [Work supported by ONR.]
The Journal of the Acoustical Society of America, 2003
The inversion of range-dependent broadband data in shallow water is presented using a previously ... more The inversion of range-dependent broadband data in shallow water is presented using a previously developed approach with rays and complex bottom plane-wave reflection coefficients [Stotts, J. Acoust. Soc. Am. 109, 2334 (2001)], allowing separation of seabed physics from water column contributions. Using geometrical optics, waterborne eigenray characteristics are calculated once and stored. Model fields are calculated by including reflection coefficient contributions from each bottom interaction and are evaluated for each perturbation of the seabed properties using simulated annealing to minimize a Bartlett-type cost function. Inversion results from range-independent and -dependent data taken during recent experiments off the coast of Florida are presented using a two-layer model. Implosive source broadband data and XBTs were recorded out to 10 km from a bottom-mounted, 52-element array 229-m deep. Grab samples obtained during the experiment show a thin, hard, crusted surface sediment. Inversions reveal an underlying softer sediment. Model time series using one inverted parameter set are compared to the data obtained from sources at different ranges. Data arrivals are compared to eigenray arrivals providing further propagation insight. Consistent inversion results from other forward models are discussed.
The Journal of the Acoustical Society of America, 2002
Time series data collected on the APL-UW/URI VLA in the East China Sea as part of the Asian Sea I... more Time series data collected on the APL-UW/URI VLA in the East China Sea as part of the Asian Sea International Acoustics Experiment are analyzed for the information they contain on the characteristics of the seabed. Sound generated by explosive sources deployed by the IOA propagates in a shallow water wave guide under downward refracting conditions, making the received field at
The Journal of the Acoustical Society of America, 2002
Low‐frequency monostatic reverberation data collected in the East China Sea on a VLA are analyzed... more Low‐frequency monostatic reverberation data collected in the East China Sea on a VLA are analyzed to infer bottom scattering strength characteristics. The VLA was deployed and the data collected by researchers from the Institute of Ocean Acoustics, Beijing, China. Reverberation data originating from ranges from 3–15 km are analyzed using coherent array processing methods to determine scattering strengths as a function of frequency and angle at the scatterer. Subaperture processing is used to separate sea surface and bottom contributions and to gain physical insight into the scattering mechanisms responsible for the observed reverberation level. Modeled transmission loss obtained from analyses of measured forward propagation data is employed within the framework of the subaperture signal processing to enable the extraction of the scattering strength. [Work supported by ONR.]
The Journal of the Acoustical Society of America, 2002
Near a shoreline an acoustic waveguide can be modeled by a wedge-shaped geometry with a penetrabl... more Near a shoreline an acoustic waveguide can be modeled by a wedge-shaped geometry with a penetrable bottom. The propagation of sound in such a waveguide was studied in a tank experiment conducted by Tindle et al. [J. Acoust. Soc. Am. 81, 275-286 (1987); 81, 287-294 (1987)]. An analysis of the time series data measured in this experiment was carried out by Royal et al. (unpublished), in which time series were simulated using a broadband, one-way, coupled normal mode approach. This analysis is extended using a two-way propagation approach that solves the integral equation form of the coupled mode equation. Also, the modal continuum is treated more realistically through the employment of a leaky mode decomposition. In particular, the importance of backscattering and coupling to the continuum is gauged by comparing the experimental data with the results of the two approaches.
The Journal of the Acoustical Society of America, 2008
On the New Jersey continental shelf ambient sound levels were recorded during tropical storm Erne... more On the New Jersey continental shelf ambient sound levels were recorded during tropical storm Ernesto that produced wind speeds up to 40 knots in early September 2006. The seabed at the position of the acoustic measurements can be approximately described as coarse sand. Differences between the ambient noise levels for the New Jersey shelf measurements and deep water reference measurements are modeled using both normal mode and ray methods. The analysis is consistent with a nonlinear frequency dependent seabed attenuation for the New Jersey site.
The Journal of the Acoustical Society of America, 2008
ABSTRACT The ambient noise level variations produced by Hurricane Ernesto were observed by the SW... more ABSTRACT The ambient noise level variations produced by Hurricane Ernesto were observed by the SWAMI32, SWAMI52 and SHARK arrays as the storm passed over the SW06 shallow water site. Microseism signals were detected in the water column near 0.1 Hz and were tracked with a beamformer over a period of several days observing variations that were very closely linked to measured surface waves. 5-75 Hz beamforming showed a sound-field dominated by local surface-noise punctuated by brief surges of noise from distant sources. Beamforming and time-domain cross-correlations showed that changes in acoustic environment on the time-scale of hours occurred at all three arrays with good correlation in time and directionality suggesting the storm induced noise-field is homogeneous over many kilometers.
The Journal of the Acoustical Society of America, 2008
Full-field inversion methods over large frequency bands and spatial scales attempt to exploit the... more Full-field inversion methods over large frequency bands and spatial scales attempt to exploit the sensitivity of the frequency and spatial dependence of the acoustic field of the properties to the seabed. A comprehensive set of broadband impulsive and narrowband tonal acoustic recordings in the 5-3000 Hz band from two Larrays separated by 20 km were made in a shallow water area on the New Jersey continental shelf during the Shallow Water 2006 (SW06) experiment. In addition, surface ship of opportunity passages on both arrays were recorded along with noise during the passage of tropical storm Ernesto. Reverberation and transmission loss data in the 25-9200 Hz band from explosive sources were also collected at a nearby site prior to the SW06 experiment. Numerous full-field geo-acoustic inversion methods and analyses of all these acoustic data with supporting range and azimuth-dependent geo-physical measurements are employed to characterize the seabed properties. For example, the analyses of these data permit inferences about the frequency-dependence of the seabed sound speed and attenuation to be made. The overlapping data types act to reduce the intrinsic ambiguities associated with inversion, quantify the spatial variability, and serve as independent validation.
The Journal of the Acoustical Society of America, 1996
A theoretical analysis of pressure time series generated by small explosive sources and recorded ... more A theoretical analysis of pressure time series generated by small explosive sources and recorded on both an HLA and a VLA deployed in the Hudson canyon region off the New Jersey coast near the AMCOR 6010 borehole is presented. The SVP in the water column has an isovelocity layer down to a depth of about 20 m followed by a strong negative gradient to about 45 m where the profile becomes approximately isovelocity to theseafloor at 73 m. This sound‐speed structure creates a unique time series structure on the VLA as a function of source range. The data are simulated with a broadband normal mode‐ approach recently discussed in the literature [J. Acoust. Soc. Am. 98, 1682–1698 (1995); IEEE J. Ocean. Eng. 21 (1) (1996)]. The representation of the spatial and temporal structure of the time series in terms of a modal structure reveals several unique aspects of the structure of the SVP in the water column and the geoacoustic structure of the bottom. The details of the modal structure of the sound field clearly def...
The Journal of the Acoustical Society of America, 1993
Data from a moving source received by three horizontally separated bottomed sensors in a shallow‐... more Data from a moving source received by three horizontally separated bottomed sensors in a shallow‐water environment are analyzed using a broadband matched‐field approach to source localization. The water depth was approximately 120 m, and the low bottom loss in the area results in low spatial coherence of the broadband field. The modeled acoustic fields are constructed via a ray model with wave‐like corrections. Localizations are made in the x‐y plane. The time evolution of the matched‐field surfaces produced from the data agree well with simulated surfaces. Matched‐field surfaces are generated successively in intervals of about 1.6 s in small search areas with a fine spatial grid to test the possibility of tracking a source. Results of the source tracking will be presented. The analysis also considers the effects of the sea floor and environmental mismatch of sea floor descriptions on localization in the context of spatial coherence. In addition the effect of varying the receiver separation on the ability...
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Papers by David Knobles