The 9th International Symposium on Modern Acoustics was held in Nanjing,China,on May 19 -22,2012,which has been introduced in an article published in Journal of Nanjing University (Natural Sciences),2012[1].As describ...The 9th International Symposium on Modern Acoustics was held in Nanjing,China,on May 19 -22,2012,which has been introduced in an article published in Journal of Nanjing University (Natural Sciences),2012[1].As described previously,after peer reviewing,a part of the original papers were selected to be published in Journal of Nanjing University(Natural Sciences),which were separated as two issues:the first has already been published in a special issue of the journal in 2012[2～19].展开更多
Wave propagation in multi-phase porous media is a significant research topic. There are a series of studies about porous media saturated with a single fluid, a solid and a fluid, two fluids, and three fluids. Some gas...Wave propagation in multi-phase porous media is a significant research topic. There are a series of studies about porous media saturated with a single fluid, a solid and a fluid, two fluids, and three fluids. Some gas hydrate-bearing sediments are typical multiphase porous media saturated with a solid(gas hydrates) and two fluids(water and gas). Based on existing theories of porous media, we develop a theory and give a comprehensive analysis of wave propagation in a poroelastic medium saturated with two fluids and a solid. Initially, we establish the constitutive relations and equations of motion. Based on Biot's approach for describing the equations of motion in fluid-saturated porous media at the macroscale,the kinetic energy density, potential energy density, and dissipative energy density are derived. After deriving the equations of motion, a plane wave analysis predicts the existence of four compressional waves, denoted P1, P2, P3, and P4 waves,and two shear waves, denoted S1 and S2 waves. Numerical examples are presented to demonstrate how velocities and attenuations of various waves behave with gas saturation, gas hydrate saturation, and frequency. A model degradation to porous media saturated with a single fluid supports the validity of the theory, which enriches the theory of multiphase porous media and provides a foundation for the evaluation of gas hydrate-bearing sediments.展开更多
Normal mode extraction has attracted extensive attention over the past few decades due to its practical value in enhancing the performance of underwater acoustic signal processing.Singular value decomposition(SVD)is a...Normal mode extraction has attracted extensive attention over the past few decades due to its practical value in enhancing the performance of underwater acoustic signal processing.Singular value decomposition(SVD)is an effective method to extract modal depth functions using vertical line arrays(VLA),particularly in scenarios when no prior environment information is available.However,the SVD method requires rigorous orthogonality conditions,and its performance severely degenerates in the presence of mode degeneracy.Consequently,the SVD approach is often not feasible in practical scenarios.This paper proposes a full rank decomposition(FRD)method to address these issues.Compared to the SVD method,the FRD method has three distinct advantages:1)the conditions that the FRD method requires are much easier to be fulfilled in practical scenarios;2)both modal depth functions and wavenumbers can be simultaneously extracted via the FRD method;3)the FRD method is not affected by the phenomenon of mode degeneracy.Numerical simulations are conducted in two types of waveguides to verify the FRD method.The impacts of environment configurations and noise levels on the precision of the extracted modal depth functions and wavenumbers are also investigated through simulation.展开更多
Surface/underwater target classification is a key topic in marine information research.However,the complex underwater environment,coupled with the diversity of target types and their variable characteristics,presents ...Surface/underwater target classification is a key topic in marine information research.However,the complex underwater environment,coupled with the diversity of target types and their variable characteristics,presents significant challenges for classifier design.For shallow-water waveguides with a negative thermocline,a residual neural network(ResNet)model based on the sound field elevation structure is constructed.This model demonstrates robust classification performance even when facing low signal-to-noise ratios and environmental mismatches.Meanwhile,to address the reduced generalization ability caused by limited labeled acoustic data,an improved ResNet model based on unsupervised domain adaptation(“proposed UDA-ResNet”)is further constructed.This model incorporates data on simulated elevation structures of the sound field to augment the training process.Adversarial training is employed to extract domain-invariant features from simulated and trial data.These strategies help reduce the negative impact caused by domain differences.Experimental results demonstrate that the proposed method shows strong surface/underwater target classification ability under limited sample sizes,thus confirming its feasibility and effectiveness.展开更多
We performed a long range acoustic propagation experiment in the South China Sea(SCS) in November 2004.The environment of the experiment was with an isothermal sound speed profile,where influence of water volume fluct...We performed a long range acoustic propagation experiment in the South China Sea(SCS) in November 2004.The environment of the experiment was with an isothermal sound speed profile,where influence of water volume fluctuation was small,meaning that bottom parameters can be well estimated from acoustic signals.We inverted the acoustic parameters of sediment by using a hybrid inversion scheme that combines the matched field processing inversion with Hamilton sediment empirical relationship and transmission loss data.The numerical results show excellent agreement with the experiment data,indicating validity of the inverted parameters.展开更多
Using deep convolutional neural networks as primary learners and a deep neural network as meta-learner, source ranging is solved as a regression problem with the ensemble learning method. Simulated acoustic data from ...Using deep convolutional neural networks as primary learners and a deep neural network as meta-learner, source ranging is solved as a regression problem with the ensemble learning method. Simulated acoustic data from the acoustic propagation model are used as the training data. Real data from an experiment in the South China Sea are used as the test data to demonstrate the performance. The results indicate that in the direct zone of deep water, signals received by a very deep receiver can be used to estimate the range of underwater sound source.Within 30 km, the mean absolute error of the range predictions is 1.0 km and the mean absolute percentage error is 7.9%.展开更多
A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by hig...A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by high-intensity ultrasonic pulses. In the finite element model, the high-power ultrasonic transducer is modeled by using a piezoelectric thermal-analogy method, and the dynamical interaction between both crack faces is modeled using a contact-impact theory. In the simulations, the frictional heating taking place at the crack faces is quantitatively calculated by using finite element thermal-structural coupling analysis, especially, the influences of acoustic chaos to plate vibration and crack heating are calculated and analysed in detail. Meanwhile, the related ultrasonic infrared images are also obtained experimentally, and the theoretical simulation results are in agreement with that of the experiments. The results show that, by using the theoretical method, a good simulation of dynamic interaction and friction heating process of the crack faces under non-chaotic or chaotic sound excitation can be obtained.展开更多
Bottom acoustic parameters play an important role in sound field prediction. Acoustic parameters in deep water are not well understood. Bottom acoustic parameters are sensitive to the transmission-loss （TL） data in ...Bottom acoustic parameters play an important role in sound field prediction. Acoustic parameters in deep water are not well understood. Bottom acoustic parameters are sensitive to the transmission-loss （TL） data in the shadow zone of deep water. We propose a multiple-step fill inversion method to invert sound speed, density and attenuation in deep water. Based on a uniform liquid hMf-space bottom model, sound speed of the bottom is inverted by using the long range TL at low frequency obtained in an acoustic propagation experiment conducted in the South China Sea （SCS） in summer 2014. Meanwhile, bottom density is estimated combining with the Hamilton sediment empirical relationship. Attenuation coefficients at different frequencies are then estimated from the TL data in the shadow zones by using the known sound speed and density as a constraint condition. The nonlinear relationship between attenuation coefficient and frequency is given in the end. Tile inverted bottom parameters can be used to forecast the transmission loss in the deep water area of SCS very we//.展开更多
Sound multipath propagation is very important for target localization and identification in different acoustical zones of deep water. In order to distinguish the multipath characteristics in deep water, the Northwest ...Sound multipath propagation is very important for target localization and identification in different acoustical zones of deep water. In order to distinguish the multipath characteristics in deep water, the Northwest Pacific Acoustic Experiment was conducted in 2015. A low-frequency horizontal line array towed at the depth of around 150 m on a receiving ship was used to receive the noise radiated by the source ship. During this experiment, a beating-splitting phenomenon in the direct zone was observed through conventional beamforming of the horizontal line array within the frequency band 160 Hz- 360 Hz. In this paper, this phenomenon is explained based on ray theory. In principle, the received signal in the direct zone of deep water arrives from two general paths including a direct one and bottom bounced one, which vary considerably in arrival angles. The split bearings correspond to the contributions of these two paths. The beating-splitting phenomenon is demonstrated by numerical simulations of the bearing-time records and experimental results, and they are well consistent with each other. Then a near-surface source ranging approach based on the arrival angles of direct path and bottom bounced path in the direct zone is presented as an application of bearing splitting and is verified by experimental results. Finally, the applicability of the proposed ranging approach for an underwater source within several hundred meters in depth in the direct zone is also analyzed and demonstrated by simulations.展开更多
A sound speed profile plays an important role in shallow water sound propagation.Concurrent with in-situ measurements,many inversion methods,such as matched-field inversion,have been put forward to invert the sound sp...A sound speed profile plays an important role in shallow water sound propagation.Concurrent with in-situ measurements,many inversion methods,such as matched-field inversion,have been put forward to invert the sound speed profile from acoustic signals.However,the time cost of matched-field inversion may be very high in replica field calculations.We studied the feasibility and robustness of an acoustic tomography scheme with matched-field processing in shallow water,and described the sound speed profile by empirical orthogonal functions.We analyzed the acoustic signals from a vertical line array in ASIAEX2001 in the East China Sea to invert sound speed profiles with estimated empirical orthogonal functions and a parallel genetic algorithm to speed up the inversion.The results show that the inverted sound speed profiles are in good agreement with conductivity-temperature-depth measurements.Moreover,a posteriori probability analysis is carried out to verify the inversion results.展开更多
The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the ...The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the deep-water acoustic field are investigated by using the experimental data obtained in the South China Sea. The experimental results show that the structures of the spatial correlation coefficient at different ranges and depths are similar to the transmission loss structure in deep water. The main reason for this phenomenon is analyzed by combining the normal mode theory with the ray theory. It is shown that the received signals in the high intensity zone mainly include one or two main pulses which are contributed by the interference of a group of waterbome modes with similar phases. The horizontal-longitudinal correlations at the same receiver depth but in different high intensity zones are analyzed. At some positions, more pulses are received in the arrival structure of the signal due to bottom reflection and the horizontal-longitudinal correlation coefficient decreases accordingly. The multi-path arrival structure of receiving signal becomes more complex with increasing receiver depth.展开更多
Underwater acoustic applications depend critically on the prediction of sound propagation,which can be significantly affected by a rough surface,especially in shallow water.This paper aims to investigate how randomly ...Underwater acoustic applications depend critically on the prediction of sound propagation,which can be significantly affected by a rough surface,especially in shallow water.This paper aims to investigate how randomly fluctuating surface influences transmission loss(TL)in shallow water.The one-dimension wind-wave spectrum,Monterey–Miami parabolic equation(MMPE)model,Monte Carlo method,and parallel computing technology are combined to investigate the effects of different sea states on sound propagation.It is shown that TL distribution properties are related to the wind speed,frequency,range,and sound speed profile.In a homogenous waveguide,with wind speed increasing,the TLs are greater and more dispersive.For a negative thermocline waveguide,when the source is above the thermocline and the receiver is below that,the effects of the rough surface are the same and more significant.When the source and receiver are both below the thermocline,the TL distributions are nearly the same for different wind speeds.The mechanism of the different TL distribution properties in the thermocline environment is explained by using ray theory.In conclusion,the statistical characteristics of TL are affected by the relative roughness of the surface,the interaction strength of the sound field with the surface,and the changes of propagating angle due to refraction.展开更多
A geoacoustic inversion method based on dispersion characteristic of normal modes is presented. An adaptive time-frequency analysis technique with a high resolution in both time and frequency domains is applied to der...A geoacoustic inversion method based on dispersion characteristic of normal modes is presented. An adaptive time-frequency analysis technique with a high resolution in both time and frequency domains is applied to derive the dispersion characteristic of normal modes from the broadband propagation signal. The bottom acoustic parameters are inverted by matching the calculated group delays of normal modes with the experimental data. Finally, some experimental results which could validate the inversion method are given.展开更多
Spatial correlation coefficient is one of the most important parameters for the description of sound propagation in shallow water. Frequency dependence of the longitudinal correlation length is still an open topic. We...Spatial correlation coefficient is one of the most important parameters for the description of sound propagation in shallow water. Frequency dependence of the longitudinal correlation length is still an open topic. We observe in a shallow water experiment that the longitudinal correlation length in units of wavelength increases with the increase of frequency. This phenomenon has not been seen in the published papers. The theoretical analysis and numerical simulations indicate that the non-linear frequency relationship of the bottom attenuation is the main cause of this phenomenon.展开更多
Relationships among the signal coherence-time of matched-field processing （MFP）, the acoustic frequency, the source-receiver range, and the sound speed standard deviation （STD） caused by internal waves in shallow ...Relationships among the signal coherence-time of matched-field processing （MFP）, the acoustic frequency, the source-receiver range, and the sound speed standard deviation （STD） caused by internal waves in shallow water, are numerically investigated based on oceanographic data from two shallow water experiments. It is found that the coherence-time can be fitted with an inverse square-root power of range, a near inverse 1 power of frequency, and inverse 1.3 power of sound speed STD.展开更多
Based on the exact solutions for the second-harmonic generations of the fundamental longitudinal and transverse waves propagating normally through a thin elastic layer between two solids, the approximate representatio...Based on the exact solutions for the second-harmonic generations of the fundamental longitudinal and transverse waves propagating normally through a thin elastic layer between two solids, the approximate representations termed as ＇nonlinear spring models＇ relating the stresses and displacements on both sides of the interface are rigorously developed by asymptotic expansions of the wave fields for an elastic layer in the limit of small thickness to wavelength ratio. The applicability for the so-called nonlinear spring models is numerically analyzed by comparison with exact solutions for the second harmonic wave reflections. The present nonlinear spring models lay a theoretical foundation to evaluate the interracial properties by nonlinear acoustic waves.展开更多
The Shipborne acoustic communication system of the submersible Shenhai Yongshi works in vertical, horizontal and slant channels according to the relative positions. For ease of use, an array combined by a vertical-con...The Shipborne acoustic communication system of the submersible Shenhai Yongshi works in vertical, horizontal and slant channels according to the relative positions. For ease of use, an array combined by a vertical-cone directional transducer and a horizontal-toroid one is installed on the mothership. Improved techniques are proposed to combat adverse channel conditions, such as frequency selectivity, non-stationary ship noise, and Doppler effects of the platform’s nonlinear movement. For coherent modulation, a turbo-coded single-carrier scheme is used. In the receiver, the sparse decision-directed Normalized Least-Mean-Square soft equalizer automatically adjusts the tap pattern and weights according to the multipath structure, the two receivers’ asymmetry, the signal’s frequency selectivity and the noise’s spectrum fluctuation. The use of turbo code in turbo equalization significantly suppresses the error floor and decreases the equalizer’s iteration times, which is verified by both the extrinsic information transfer charts and bit-error-rate performance. For noncoherent modulation, a concatenated error correction scheme of nonbinary convolutional code and Hadamard code is adopted to utilize full frequency diversity. Robust and lowcomplexity synchronization techniques in the time and Doppler domains are proposed. Sea trials with the submersible to a maximum depth of over 4500 m show that the shipborne communication system performs robustly during the adverse conditions. From the ten-thousand communication records in the 28 dives in 2017, the failure rate of the coherent frames and that of the noncoherent packets are both below 10%, where both synchronization errors and decoding errors are taken into account.展开更多
New experimental measurements of signal coherence in shallow water are presented. For signals with Iow fre quencies of about 500 Hz in iso-velocity shallow water with a silt-sand bottom and a water depth of about 45 t...New experimental measurements of signal coherence in shallow water are presented. For signals with Iow fre quencies of about 500 Hz in iso-velocity shallow water with a silt-sand bottom and a water depth of about 45 tn, the vertical coherence has no distinct depth dependence at ranges of 18.5, 55.5 and 92.5 kin, but it has obvious range dependence. The horizontal coherence lengths are all greater than 40 wavelengths, and the time coherence lengths are all greater than 510s at these ranges. These experimental results show that a low-frequency acoustic field has strong spatial coherence and temporal stability in iso-velocity shallow water.展开更多
The estimation of ocean sound speed profiles(SSPs)requires the inversion of an acoustic field using limited observations.Such inverse problems are underdetermined,and require regularization to ensure physically realis...The estimation of ocean sound speed profiles(SSPs)requires the inversion of an acoustic field using limited observations.Such inverse problems are underdetermined,and require regularization to ensure physically realistic solutions.The empirical orthonormal function(EOF)is capable of a very large compression of the data set.In this paper,the non-linear response of the sound pressure to SSP is linearized using a first order Taylor expansion,and the pressure is expanded in a sparse domain using EOFs.Since the parameters of the inverse model are sparse,compressive sensing(CS)can help solve such underdetermined problems accurately,efficiently,and with enhanced resolution.Here,the orthogonal matching pursuit(OMP)is used to estimate range-independent acoustic SSPs using the simulated acoustic field.The superior resolution of OMP is demonstrated with the SSP data from the South China Sea experiment.By shortening the duration of the training set,the temporal correlation between EOF and test sets is enhanced,and the accuracy of sound velocity inversion is improved.The SSP estimation error versus depth is calculated,and the 99%confidence interval of error is within±0.6 m/s.The 82%of mean absolute error(MAE)is less than 1 m/s.It is shown that SSPs can be well estimated using OMP.展开更多
文摘The 9th International Symposium on Modern Acoustics was held in Nanjing,China,on May 19 -22,2012,which has been introduced in an article published in Journal of Nanjing University (Natural Sciences),2012[1].As described previously,after peer reviewing,a part of the original papers were selected to be published in Journal of Nanjing University(Natural Sciences),which were separated as two issues:the first has already been published in a special issue of the journal in 2012[2～19].
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12304496 and 12334019)。
文摘Wave propagation in multi-phase porous media is a significant research topic. There are a series of studies about porous media saturated with a single fluid, a solid and a fluid, two fluids, and three fluids. Some gas hydrate-bearing sediments are typical multiphase porous media saturated with a solid(gas hydrates) and two fluids(water and gas). Based on existing theories of porous media, we develop a theory and give a comprehensive analysis of wave propagation in a poroelastic medium saturated with two fluids and a solid. Initially, we establish the constitutive relations and equations of motion. Based on Biot's approach for describing the equations of motion in fluid-saturated porous media at the macroscale,the kinetic energy density, potential energy density, and dissipative energy density are derived. After deriving the equations of motion, a plane wave analysis predicts the existence of four compressional waves, denoted P1, P2, P3, and P4 waves,and two shear waves, denoted S1 and S2 waves. Numerical examples are presented to demonstrate how velocities and attenuations of various waves behave with gas saturation, gas hydrate saturation, and frequency. A model degradation to porous media saturated with a single fluid supports the validity of the theory, which enriches the theory of multiphase porous media and provides a foundation for the evaluation of gas hydrate-bearing sediments.
基金supported by the National Natural Science Foundation of China(Nos.12304504,12304506 and U22 A2012)the Youth Innovation Promotion Association,Chinese Academy of Sciences(No.2021023)+1 种基金the Strategy Priority Research Program(Category B)of Chinese Academy of Sciences(Nos.XDB0700100 and XDB0700000)the Natural Science Foundation of Tianjin(No.22JCYBJC00070).
文摘Normal mode extraction has attracted extensive attention over the past few decades due to its practical value in enhancing the performance of underwater acoustic signal processing.Singular value decomposition(SVD)is an effective method to extract modal depth functions using vertical line arrays(VLA),particularly in scenarios when no prior environment information is available.However,the SVD method requires rigorous orthogonality conditions,and its performance severely degenerates in the presence of mode degeneracy.Consequently,the SVD approach is often not feasible in practical scenarios.This paper proposes a full rank decomposition(FRD)method to address these issues.Compared to the SVD method,the FRD method has three distinct advantages:1)the conditions that the FRD method requires are much easier to be fulfilled in practical scenarios;2)both modal depth functions and wavenumbers can be simultaneously extracted via the FRD method;3)the FRD method is not affected by the phenomenon of mode degeneracy.Numerical simulations are conducted in two types of waveguides to verify the FRD method.The impacts of environment configurations and noise levels on the precision of the extracted modal depth functions and wavenumbers are also investigated through simulation.
基金supported by the National Natural Science Foundation of China(Grant Nos.62471024 and 62301183)the Open Research Fund of Hanjiang Laboratory(KF2024001).
文摘Surface/underwater target classification is a key topic in marine information research.However,the complex underwater environment,coupled with the diversity of target types and their variable characteristics,presents significant challenges for classifier design.For shallow-water waveguides with a negative thermocline,a residual neural network(ResNet)model based on the sound field elevation structure is constructed.This model demonstrates robust classification performance even when facing low signal-to-noise ratios and environmental mismatches.Meanwhile,to address the reduced generalization ability caused by limited labeled acoustic data,an improved ResNet model based on unsupervised domain adaptation(“proposed UDA-ResNet”)is further constructed.This model incorporates data on simulated elevation structures of the sound field to augment the training process.Adversarial training is employed to extract domain-invariant features from simulated and trial data.These strategies help reduce the negative impact caused by domain differences.Experimental results demonstrate that the proposed method shows strong surface/underwater target classification ability under limited sample sizes,thus confirming its feasibility and effectiveness.
基金This work was supported by grants fromthe National Natural Science Foundation of China(No.30470564,30670695)an international joint grantfromthe NSFC+1 种基金the Russian Foundation of Basic Research(NSFC:No.30611120056RFBR:No.05-04-39008)
基金Supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (No.KZCX1-YW-12-02)the National Natural Science Foundation of China (Nos.10974218 and 10734100)
文摘We performed a long range acoustic propagation experiment in the South China Sea(SCS) in November 2004.The environment of the experiment was with an isothermal sound speed profile,where influence of water volume fluctuation was small,meaning that bottom parameters can be well estimated from acoustic signals.We inverted the acoustic parameters of sediment by using a hybrid inversion scheme that combines the matched field processing inversion with Hamilton sediment empirical relationship and transmission loss data.The numerical results show excellent agreement with the experiment data,indicating validity of the inverted parameters.
基金the National Natural Science Foundation of China under Grant Nos 11434012 and 11874061
文摘Using deep convolutional neural networks as primary learners and a deep neural network as meta-learner, source ranging is solved as a regression problem with the ensemble learning method. Simulated acoustic data from the acoustic propagation model are used as the training data. Real data from an experiment in the South China Sea are used as the test data to demonstrate the performance. The results indicate that in the direct zone of deep water, signals received by a very deep receiver can be used to estimate the range of underwater sound source.Within 30 km, the mean absolute error of the range predictions is 1.0 km and the mean absolute percentage error is 7.9%.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10574073)
文摘A three-dimensional thermo-mechanical coupled finite element model is built up to simulate the phenomena of dynamical contact and frictional heating of crack faces when the plate containing the crack is excited by high-intensity ultrasonic pulses. In the finite element model, the high-power ultrasonic transducer is modeled by using a piezoelectric thermal-analogy method, and the dynamical interaction between both crack faces is modeled using a contact-impact theory. In the simulations, the frictional heating taking place at the crack faces is quantitatively calculated by using finite element thermal-structural coupling analysis, especially, the influences of acoustic chaos to plate vibration and crack heating are calculated and analysed in detail. Meanwhile, the related ultrasonic infrared images are also obtained experimentally, and the theoretical simulation results are in agreement with that of the experiments. The results show that, by using the theoretical method, a good simulation of dynamic interaction and friction heating process of the crack faces under non-chaotic or chaotic sound excitation can be obtained.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11434012,41561144006,11174312 and 11404366
文摘Bottom acoustic parameters play an important role in sound field prediction. Acoustic parameters in deep water are not well understood. Bottom acoustic parameters are sensitive to the transmission-loss （TL） data in the shadow zone of deep water. We propose a multiple-step fill inversion method to invert sound speed, density and attenuation in deep water. Based on a uniform liquid hMf-space bottom model, sound speed of the bottom is inverted by using the long range TL at low frequency obtained in an acoustic propagation experiment conducted in the South China Sea （SCS） in summer 2014. Meanwhile, bottom density is estimated combining with the Hamilton sediment empirical relationship. Attenuation coefficients at different frequencies are then estimated from the TL data in the shadow zones by using the known sound speed and density as a constraint condition. The nonlinear relationship between attenuation coefficient and frequency is given in the end. Tile inverted bottom parameters can be used to forecast the transmission loss in the deep water area of SCS very we//.
基金Project supported by the Program of One Hundred Talented People of the Chinese Academy of SciencesNational Natural Science Foundation of China(Grant Nos.11434012 and 41561144006)
文摘Sound multipath propagation is very important for target localization and identification in different acoustical zones of deep water. In order to distinguish the multipath characteristics in deep water, the Northwest Pacific Acoustic Experiment was conducted in 2015. A low-frequency horizontal line array towed at the depth of around 150 m on a receiving ship was used to receive the noise radiated by the source ship. During this experiment, a beating-splitting phenomenon in the direct zone was observed through conventional beamforming of the horizontal line array within the frequency band 160 Hz- 360 Hz. In this paper, this phenomenon is explained based on ray theory. In principle, the received signal in the direct zone of deep water arrives from two general paths including a direct one and bottom bounced one, which vary considerably in arrival angles. The split bearings correspond to the contributions of these two paths. The beating-splitting phenomenon is demonstrated by numerical simulations of the bearing-time records and experimental results, and they are well consistent with each other. Then a near-surface source ranging approach based on the arrival angles of direct path and bottom bounced path in the direct zone is presented as an application of bearing splitting and is verified by experimental results. Finally, the applicability of the proposed ranging approach for an underwater source within several hundred meters in depth in the direct zone is also analyzed and demonstrated by simulations.
基金Supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (No.KZCX1-YW-12-02)the National Natural Science Foundation of China (Nos.10974218,10734100)
文摘A sound speed profile plays an important role in shallow water sound propagation.Concurrent with in-situ measurements,many inversion methods,such as matched-field inversion,have been put forward to invert the sound speed profile from acoustic signals.However,the time cost of matched-field inversion may be very high in replica field calculations.We studied the feasibility and robustness of an acoustic tomography scheme with matched-field processing in shallow water,and described the sound speed profile by empirical orthogonal functions.We analyzed the acoustic signals from a vertical line array in ASIAEX2001 in the East China Sea to invert sound speed profiles with estimated empirical orthogonal functions and a parallel genetic algorithm to speed up the inversion.The results show that the inverted sound speed profiles are in good agreement with conductivity-temperature-depth measurements.Moreover,a posteriori probability analysis is carried out to verify the inversion results.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11434012 and 41561144006)
文摘The spatial correlations of acoustic field have important implications for underwater target detection and other ap- plications in deep water. In this paper, the spatial correlations of the high intensity zone in the deep-water acoustic field are investigated by using the experimental data obtained in the South China Sea. The experimental results show that the structures of the spatial correlation coefficient at different ranges and depths are similar to the transmission loss structure in deep water. The main reason for this phenomenon is analyzed by combining the normal mode theory with the ray theory. It is shown that the received signals in the high intensity zone mainly include one or two main pulses which are contributed by the interference of a group of waterbome modes with similar phases. The horizontal-longitudinal correlations at the same receiver depth but in different high intensity zones are analyzed. At some positions, more pulses are received in the arrival structure of the signal due to bottom reflection and the horizontal-longitudinal correlation coefficient decreases accordingly. The multi-path arrival structure of receiving signal becomes more complex with increasing receiver depth.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11434012,11874061,and 41561144006)
文摘Underwater acoustic applications depend critically on the prediction of sound propagation,which can be significantly affected by a rough surface,especially in shallow water.This paper aims to investigate how randomly fluctuating surface influences transmission loss(TL)in shallow water.The one-dimension wind-wave spectrum,Monterey–Miami parabolic equation(MMPE)model,Monte Carlo method,and parallel computing technology are combined to investigate the effects of different sea states on sound propagation.It is shown that TL distribution properties are related to the wind speed,frequency,range,and sound speed profile.In a homogenous waveguide,with wind speed increasing,the TLs are greater and more dispersive.For a negative thermocline waveguide,when the source is above the thermocline and the receiver is below that,the effects of the rough surface are the same and more significant.When the source and receiver are both below the thermocline,the TL distributions are nearly the same for different wind speeds.The mechanism of the different TL distribution properties in the thermocline environment is explained by using ray theory.In conclusion,the statistical characteristics of TL are affected by the relative roughness of the surface,the interaction strength of the sound field with the surface,and the changes of propagating angle due to refraction.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10474112 and 10234050.
文摘A geoacoustic inversion method based on dispersion characteristic of normal modes is presented. An adaptive time-frequency analysis technique with a high resolution in both time and frequency domains is applied to derive the dispersion characteristic of normal modes from the broadband propagation signal. The bottom acoustic parameters are inverted by matching the calculated group delays of normal modes with the experimental data. Finally, some experimental results which could validate the inversion method are given.
基金Supported by the National Natural Science Foundation of China under Grand No 10734100
文摘Spatial correlation coefficient is one of the most important parameters for the description of sound propagation in shallow water. Frequency dependence of the longitudinal correlation length is still an open topic. We observe in a shallow water experiment that the longitudinal correlation length in units of wavelength increases with the increase of frequency. This phenomenon has not been seen in the published papers. The theoretical analysis and numerical simulations indicate that the non-linear frequency relationship of the bottom attenuation is the main cause of this phenomenon.
基金Supported by Knowledge Innovation Program of the Chinese Academy of Sciences under Grant No KZCX1-YW-12-2, and the National Natural Science Foundation of China under Grant No 10734100.
文摘Relationships among the signal coherence-time of matched-field processing （MFP）, the acoustic frequency, the source-receiver range, and the sound speed standard deviation （STD） caused by internal waves in shallow water, are numerically investigated based on oceanographic data from two shallow water experiments. It is found that the coherence-time can be fitted with an inverse square-root power of range, a near inverse 1 power of frequency, and inverse 1.3 power of sound speed STD.
基金Supported by the National Natural Science Foundation of China under Grant No 10834009.
文摘Based on the exact solutions for the second-harmonic generations of the fundamental longitudinal and transverse waves propagating normally through a thin elastic layer between two solids, the approximate representations termed as ＇nonlinear spring models＇ relating the stresses and displacements on both sides of the interface are rigorously developed by asymptotic expansions of the wave fields for an elastic layer in the limit of small thickness to wavelength ratio. The applicability for the so-called nonlinear spring models is numerically analyzed by comparison with exact solutions for the second harmonic wave reflections. The present nonlinear spring models lay a theoretical foundation to evaluate the interracial properties by nonlinear acoustic waves.
基金financially supported by the National Natural Science Foundation of China(Grant No.61471351)the National Key Research and Development Program of China(Grant Nos.2016YFC0300300 and 2016YFC0300605)the National High Technology Research and Development Program of China(863 Program,Grant No.2009AA093301)
文摘The Shipborne acoustic communication system of the submersible Shenhai Yongshi works in vertical, horizontal and slant channels according to the relative positions. For ease of use, an array combined by a vertical-cone directional transducer and a horizontal-toroid one is installed on the mothership. Improved techniques are proposed to combat adverse channel conditions, such as frequency selectivity, non-stationary ship noise, and Doppler effects of the platform’s nonlinear movement. For coherent modulation, a turbo-coded single-carrier scheme is used. In the receiver, the sparse decision-directed Normalized Least-Mean-Square soft equalizer automatically adjusts the tap pattern and weights according to the multipath structure, the two receivers’ asymmetry, the signal’s frequency selectivity and the noise’s spectrum fluctuation. The use of turbo code in turbo equalization significantly suppresses the error floor and decreases the equalizer’s iteration times, which is verified by both the extrinsic information transfer charts and bit-error-rate performance. For noncoherent modulation, a concatenated error correction scheme of nonbinary convolutional code and Hadamard code is adopted to utilize full frequency diversity. Robust and lowcomplexity synchronization techniques in the time and Doppler domains are proposed. Sea trials with the submersible to a maximum depth of over 4500 m show that the shipborne communication system performs robustly during the adverse conditions. From the ten-thousand communication records in the 28 dives in 2017, the failure rate of the coherent frames and that of the noncoherent packets are both below 10%, where both synchronization errors and decoding errors are taken into account.
基金Supported by the National Natural Science Foundation of China under Grant No.19734050。
文摘New experimental measurements of signal coherence in shallow water are presented. For signals with Iow fre quencies of about 500 Hz in iso-velocity shallow water with a silt-sand bottom and a water depth of about 45 tn, the vertical coherence has no distinct depth dependence at ranges of 18.5, 55.5 and 92.5 kin, but it has obvious range dependence. The horizontal coherence lengths are all greater than 40 wavelengths, and the time coherence lengths are all greater than 510s at these ranges. These experimental results show that a low-frequency acoustic field has strong spatial coherence and temporal stability in iso-velocity shallow water.
基金The National Natural Science Foundation of China under contract No.11704225the Shandong Provincial Natural Science Foundation under contract No.ZR2016AQ23+3 种基金the State Key Laboratory of Acoustics,Chinese Academy of Sciences under contract No.SKLA201902the National Key Research and Development Program of China contract No.2018YFC1405900the SDUST Research Fund under contract No.2019TDJH103the Talent Introduction Plan for Youth Innovation Team in Universities of Shandong Province(Innovation Team of Satellite Positioning and Navigation)
文摘The estimation of ocean sound speed profiles(SSPs)requires the inversion of an acoustic field using limited observations.Such inverse problems are underdetermined,and require regularization to ensure physically realistic solutions.The empirical orthonormal function(EOF)is capable of a very large compression of the data set.In this paper,the non-linear response of the sound pressure to SSP is linearized using a first order Taylor expansion,and the pressure is expanded in a sparse domain using EOFs.Since the parameters of the inverse model are sparse,compressive sensing(CS)can help solve such underdetermined problems accurately,efficiently,and with enhanced resolution.Here,the orthogonal matching pursuit(OMP)is used to estimate range-independent acoustic SSPs using the simulated acoustic field.The superior resolution of OMP is demonstrated with the SSP data from the South China Sea experiment.By shortening the duration of the training set,the temporal correlation between EOF and test sets is enhanced,and the accuracy of sound velocity inversion is improved.The SSP estimation error versus depth is calculated,and the 99%confidence interval of error is within±0.6 m/s.The 82%of mean absolute error(MAE)is less than 1 m/s.It is shown that SSPs can be well estimated using OMP.
