Journal of The Acoustical Society of America, 2003
Data from the ASIAEX East China Sea (ECS) experiment is used to estimate sediment attenuation coe... more Data from the ASIAEX East China Sea (ECS) experiment is used to estimate sediment attenuation coefficients as a function of frequency and depth. The ECS experiment offers a number of independent measures of sediment parameters using seismic and chirp surveys, gravity and piston cores and historic data. Modal amplitude ratios for modes 1 to 3 are used to obtain the
A bstract-Wideband acoustic propagation in shallow water has a unique arrival structure .due to m... more A bstract-Wideband acoustic propagation in shallow water has a unique arrival structure .due to modal group speed dispersion. It is possible to unravel the modal dispersion characteristics using a proper time-frequency (TF) analysis. During the Asian Seas International Acoustics Experiment (ASIAEX) - East China Sea (ECS) experiment, signals collected by the vertical arrays have been processed using several time-frequency analysis
Oceans 2003. Celebrating the Past ... Teaming Toward the Future (IEEE Cat. No.03CH37492), 2003
Wideband acoustic propagation in shallow water has a unique arrival structure due to modal group ... more Wideband acoustic propagation in shallow water has a unique arrival structure due to modal group speed dispersion. It is possible to unravel the modal dispersion characteristics using a proper time-frequency (TF) analysis. During the Asian Seas International Acoustics Experiment (ASIAEX) - East China Sea (ECS) experiment, signal collected by the vertical arrays have been processed using several time-frequency analysis techniques.
Acoustic methods (sonars) offer a potential tool for detecting and tracking of underwater swimmer... more Acoustic methods (sonars) offer a potential tool for detecting and tracking of underwater swimmers. The main unknown in assessing the feasibility of using sonar to detect swimmers is their target strength. The target strength of diver with tanks, buoyancy control, wet or dry suit, etc. is a complicated function of aspect angle and frequency. The detection range for a diver will depend strongly on the target strength and very little data are available in the literature on this topic. This dearth of information limits the ability of sonar engineers to design a detection system. Our study addresses this issue both experimentally and theoretically. As part of this study target strength measurements made in the field were compared with theoretical models. Measurements are being conducted using Farsounder FS-3 phased array sonar with a center frequency of 60 kHz. Tests will be carried out in shallow water using a diver at different orientations, depths and ranges. Target strength modeling was performed using simple cylindrical models and more sophisticated techniques. Existing target strength models for finite cylindrical shapes derived by Gaunaurd (1985) were used as initial approximations. A relatively new technique for modeling acoustic scattering by axisymmetric finite-length bodies using a three-dimensional Fourier mapping method developed by Reeder and Stanton (2004) was compared to the data.
The Journal of the Acoustical Society of America, 2009
ABSTRACT A noise budget is a listing of the various sources of acoustic noise and their associate... more ABSTRACT A noise budget is a listing of the various sources of acoustic noise and their associated ranking by importance. A number of different types of budgets can be conceived using various acoustic measures such as intensity, energy, or duration of maximum amplitude level. These budgets are typically parameterized by frequency and are usually computed over 13 octave bands. As part of the environmental assessment of the proposed offshore wind power generation project under the Rhode Island Special Area Management Plan (SAMP), noise measurements were made using the Passive Acoustic Listener (PAL) systems off the coast of Rhode Island prior to the installation of any wind power facilities. Two PALs were deployed within two miles of Block Island in water depths of 20 m from October 6 to November 11, 2008. The data included noise spectra and source identification every 3 min. Short snapshots of unusual sounds were also recorded. From this data, the ocean acoustic noise budget is computed with contributions from shipping, windwaves, marine mammals, and rain from 500 Hz to 50 kHz. The ship noise data is correlated with ship traffic data from the Automatic Identification System (AIS). [Funding provided by the Rhode Island Office of Energy Resources.].
The Journal of the Acoustical Society of America, 2010
ABSTRACT During the Shallow Water 2006 (SW06) experiment, a J-15 acoustic source deployed from th... more ABSTRACT During the Shallow Water 2006 (SW06) experiment, a J-15 acoustic source deployed from the Research Vessel Sharp transmitted broadband (100-500 Hz) chirp signals 15 km away from a vertical line array. The array was intentionally positioned near the shelf-break front and in an area where internal waves are known to occur. During the same time an internal wave, "Event 44," passed through the sound field such that the internal wave front was near parallel to the acoustic transmission path. Measured data show substantial intensity fluctuations that vary over time and space due to complex multimode and multipath (both 2- and 3-D) interference patterns. This presentation compares 3-D modeling results using the experimental geometry, acoustic signal parameters, and a simulated oceanographic environment based on environmental moorings and ship-born sensors to mimic the measured internal wave event. A modified version of the 3-D Monterey-Miami parabolic equation (MMPE) code which incorporates a user-defined sound speed field is used. Measured and modeled intensity fluctuations are compared during dominating horizontal regimes such as refraction, ducting, and "anti-ducting." Modal-dependent time-arrival analysis during the different horizontal regimes is examined. [Work sponsored by the Office of Naval Research.].
The Journal of the Acoustical Society of America, 2002
Dispersive acoustic signals contain significant amounts of information concerning the shallow wat... more Dispersive acoustic signals contain significant amounts of information concerning the shallow water environment structure. It is possible to unravel the modal propagation dispersion characteristics using a proper time-frequency analysis. Recent experiments such as ShelfBreak Primer and ASIAEX collected long range propagation data in shallow water on vertical line arrays from SUS charge explosive sources. Signals collected by the vertical arrays
The Journal of the Acoustical Society of America, 2003
This article discusses inversions for bottom geoacoustic properties using broadband acoustic sign... more 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.
The Journal of the Acoustical Society of America, 2007
Combustive sound source (CSS) data collected on single hydrophone receiving units, in water depth... more Combustive sound source (CSS) data collected on single hydrophone receiving units, in water depths ranging from 65 to 110 m, during the Shallow Water 2006 experiment clearly show modal dispersion effects and are suitable for modal geoacoustic inversions. CSS shots were set off at 26 m depth in 100 m of water. The inversions performed are based on an iterative scheme using dispersion-based short time Fourier transform in which each time-frequency tiling is adaptively rotated in the time-frequency plane, depending on the local wave dispersion. Results of the inversions are found to compare favorably to local core data.
The Journal of the Acoustical Society of America, 2003
A mode travel time based technique for geoacoustic inversions has been developed using broadband ... more A mode travel time based technique for geoacoustic inversions has been developed using broadband explosive sources [Potty et al., J. Acoust. Soc. Am. 108, 973-986 (2000)]. In this inversion scheme we search for various parameters including water depth, sound speed in the water column represented by Empirical Orthogonal Function (EOFs), compressional wave speed in the sediment and sub-base, thickness of
The Journal of the Acoustical Society of America, 2012
ABSTRACT In shallow water the assumption of range independence fails in conditions of rapidly-var... more ABSTRACT In shallow water the assumption of range independence fails in conditions of rapidly-varying bathymetry and/or horizontal sound speed. In these environments, the modes of vibration of the acoustic wave equation become coupled, with a transfer of energy between adjacent modes occurring upon traversing a horizontal change of environment. In this talk, we will consider some simple applications of mode conversions due to variable bathymetry. Results will be compared to closed form propagation solutions in constant-slope wedge environments. The ultimate goal of this research is the development of a fully non-adiabatic range-dependent mode solution which retains analytical integrity while executing in a time window that is tactically useful for warfare applications.
The Journal of the Acoustical Society of America, 2011
ABSTRACT Recent research has highlighted the effect of shear on compressional wave attenuation an... more ABSTRACT Recent research has highlighted the effect of shear on compressional wave attenuation and its frequency dependence and modal arrival times near the Airy Phase. Shear properties of sediments are directly related to the strength of the sediments in geotechnical applications. One of the most promising approaches to estimate shear speed is to invert the shear speed profile using the dispersion of seismo-acoustic interface (Scholte) waves that travel along the sediment-water boundary. A shear measurement system is being developed at the University of Rhode Island based on this concept and data collected during a sea-test is presented along with preliminary results.
Journal of The Acoustical Society of America, 2003
Data from the ASIAEX East China Sea (ECS) experiment is used to estimate sediment attenuation coe... more Data from the ASIAEX East China Sea (ECS) experiment is used to estimate sediment attenuation coefficients as a function of frequency and depth. The ECS experiment offers a number of independent measures of sediment parameters using seismic and chirp surveys, gravity and piston cores and historic data. Modal amplitude ratios for modes 1 to 3 are used to obtain the
A bstract-Wideband acoustic propagation in shallow water has a unique arrival structure .due to m... more A bstract-Wideband acoustic propagation in shallow water has a unique arrival structure .due to modal group speed dispersion. It is possible to unravel the modal dispersion characteristics using a proper time-frequency (TF) analysis. During the Asian Seas International Acoustics Experiment (ASIAEX) - East China Sea (ECS) experiment, signals collected by the vertical arrays have been processed using several time-frequency analysis
Oceans 2003. Celebrating the Past ... Teaming Toward the Future (IEEE Cat. No.03CH37492), 2003
Wideband acoustic propagation in shallow water has a unique arrival structure due to modal group ... more Wideband acoustic propagation in shallow water has a unique arrival structure due to modal group speed dispersion. It is possible to unravel the modal dispersion characteristics using a proper time-frequency (TF) analysis. During the Asian Seas International Acoustics Experiment (ASIAEX) - East China Sea (ECS) experiment, signal collected by the vertical arrays have been processed using several time-frequency analysis techniques.
Acoustic methods (sonars) offer a potential tool for detecting and tracking of underwater swimmer... more Acoustic methods (sonars) offer a potential tool for detecting and tracking of underwater swimmers. The main unknown in assessing the feasibility of using sonar to detect swimmers is their target strength. The target strength of diver with tanks, buoyancy control, wet or dry suit, etc. is a complicated function of aspect angle and frequency. The detection range for a diver will depend strongly on the target strength and very little data are available in the literature on this topic. This dearth of information limits the ability of sonar engineers to design a detection system. Our study addresses this issue both experimentally and theoretically. As part of this study target strength measurements made in the field were compared with theoretical models. Measurements are being conducted using Farsounder FS-3 phased array sonar with a center frequency of 60 kHz. Tests will be carried out in shallow water using a diver at different orientations, depths and ranges. Target strength modeling was performed using simple cylindrical models and more sophisticated techniques. Existing target strength models for finite cylindrical shapes derived by Gaunaurd (1985) were used as initial approximations. A relatively new technique for modeling acoustic scattering by axisymmetric finite-length bodies using a three-dimensional Fourier mapping method developed by Reeder and Stanton (2004) was compared to the data.
The Journal of the Acoustical Society of America, 2009
ABSTRACT A noise budget is a listing of the various sources of acoustic noise and their associate... more ABSTRACT A noise budget is a listing of the various sources of acoustic noise and their associated ranking by importance. A number of different types of budgets can be conceived using various acoustic measures such as intensity, energy, or duration of maximum amplitude level. These budgets are typically parameterized by frequency and are usually computed over 13 octave bands. As part of the environmental assessment of the proposed offshore wind power generation project under the Rhode Island Special Area Management Plan (SAMP), noise measurements were made using the Passive Acoustic Listener (PAL) systems off the coast of Rhode Island prior to the installation of any wind power facilities. Two PALs were deployed within two miles of Block Island in water depths of 20 m from October 6 to November 11, 2008. The data included noise spectra and source identification every 3 min. Short snapshots of unusual sounds were also recorded. From this data, the ocean acoustic noise budget is computed with contributions from shipping, windwaves, marine mammals, and rain from 500 Hz to 50 kHz. The ship noise data is correlated with ship traffic data from the Automatic Identification System (AIS). [Funding provided by the Rhode Island Office of Energy Resources.].
The Journal of the Acoustical Society of America, 2010
ABSTRACT During the Shallow Water 2006 (SW06) experiment, a J-15 acoustic source deployed from th... more ABSTRACT During the Shallow Water 2006 (SW06) experiment, a J-15 acoustic source deployed from the Research Vessel Sharp transmitted broadband (100-500 Hz) chirp signals 15 km away from a vertical line array. The array was intentionally positioned near the shelf-break front and in an area where internal waves are known to occur. During the same time an internal wave, "Event 44," passed through the sound field such that the internal wave front was near parallel to the acoustic transmission path. Measured data show substantial intensity fluctuations that vary over time and space due to complex multimode and multipath (both 2- and 3-D) interference patterns. This presentation compares 3-D modeling results using the experimental geometry, acoustic signal parameters, and a simulated oceanographic environment based on environmental moorings and ship-born sensors to mimic the measured internal wave event. A modified version of the 3-D Monterey-Miami parabolic equation (MMPE) code which incorporates a user-defined sound speed field is used. Measured and modeled intensity fluctuations are compared during dominating horizontal regimes such as refraction, ducting, and "anti-ducting." Modal-dependent time-arrival analysis during the different horizontal regimes is examined. [Work sponsored by the Office of Naval Research.].
The Journal of the Acoustical Society of America, 2002
Dispersive acoustic signals contain significant amounts of information concerning the shallow wat... more Dispersive acoustic signals contain significant amounts of information concerning the shallow water environment structure. It is possible to unravel the modal propagation dispersion characteristics using a proper time-frequency analysis. Recent experiments such as ShelfBreak Primer and ASIAEX collected long range propagation data in shallow water on vertical line arrays from SUS charge explosive sources. Signals collected by the vertical arrays
The Journal of the Acoustical Society of America, 2003
This article discusses inversions for bottom geoacoustic properties using broadband acoustic sign... more 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.
The Journal of the Acoustical Society of America, 2007
Combustive sound source (CSS) data collected on single hydrophone receiving units, in water depth... more Combustive sound source (CSS) data collected on single hydrophone receiving units, in water depths ranging from 65 to 110 m, during the Shallow Water 2006 experiment clearly show modal dispersion effects and are suitable for modal geoacoustic inversions. CSS shots were set off at 26 m depth in 100 m of water. The inversions performed are based on an iterative scheme using dispersion-based short time Fourier transform in which each time-frequency tiling is adaptively rotated in the time-frequency plane, depending on the local wave dispersion. Results of the inversions are found to compare favorably to local core data.
The Journal of the Acoustical Society of America, 2003
A mode travel time based technique for geoacoustic inversions has been developed using broadband ... more A mode travel time based technique for geoacoustic inversions has been developed using broadband explosive sources [Potty et al., J. Acoust. Soc. Am. 108, 973-986 (2000)]. In this inversion scheme we search for various parameters including water depth, sound speed in the water column represented by Empirical Orthogonal Function (EOFs), compressional wave speed in the sediment and sub-base, thickness of
The Journal of the Acoustical Society of America, 2012
ABSTRACT In shallow water the assumption of range independence fails in conditions of rapidly-var... more ABSTRACT In shallow water the assumption of range independence fails in conditions of rapidly-varying bathymetry and/or horizontal sound speed. In these environments, the modes of vibration of the acoustic wave equation become coupled, with a transfer of energy between adjacent modes occurring upon traversing a horizontal change of environment. In this talk, we will consider some simple applications of mode conversions due to variable bathymetry. Results will be compared to closed form propagation solutions in constant-slope wedge environments. The ultimate goal of this research is the development of a fully non-adiabatic range-dependent mode solution which retains analytical integrity while executing in a time window that is tactically useful for warfare applications.
The Journal of the Acoustical Society of America, 2011
ABSTRACT Recent research has highlighted the effect of shear on compressional wave attenuation an... more ABSTRACT Recent research has highlighted the effect of shear on compressional wave attenuation and its frequency dependence and modal arrival times near the Airy Phase. Shear properties of sediments are directly related to the strength of the sediments in geotechnical applications. One of the most promising approaches to estimate shear speed is to invert the shear speed profile using the dispersion of seismo-acoustic interface (Scholte) waves that travel along the sediment-water boundary. A shear measurement system is being developed at the University of Rhode Island based on this concept and data collected during a sea-test is presented along with preliminary results.
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Papers by Gopu Potty