Multiple linear regression （MLR） method was applied to quantify the effects of the net heat flux （NHF）, the net freshwater flux （NFF） and the wind stress on the mixed layer depth （MLD） of the South China Sea ...Multiple linear regression （MLR） method was applied to quantify the effects of the net heat flux （NHF）, the net freshwater flux （NFF） and the wind stress on the mixed layer depth （MLD） of the South China Sea （SCS） based on the simple ocean data assimilation （SODA） dataset. The spatio-temporal distributions of the MLD, the buoyancy flux （combining the NHF and the NFF） and the wind stress of the SCS were presented. Then using an oceanic vertical mixing model, the MLD after a certain time under the same initial conditions but various pairs of boundary conditions （the three factors） was simulated. Applying the MLR method to the results, regression equations which modeling the relationship between the simulated MLD and the three factors were calculated. The equations indicate that when the NHF was negative, it was the primary driver of the mixed layer deepening; and when the NHF was positive, the wind stress played a more important role than that of the NHF while the NFF had the least effect. When the NHF was positive, the relative quantitative effects of the wind stress, the NHF, and the NFF were about i0, 6 and 2. The above conclusions were applied to explaining the spatio-temporal distributions of the MLD in the SCS and thus proved to be valid.展开更多
Discrete noise source suppression in underwa-ter acoustic channel has attracted great attention in recent years. The paper proposes a new principle for dealing with the problem. This new principle is called matched fi...Discrete noise source suppression in underwa-ter acoustic channel has attracted great attention in recent years. The paper proposes a new principle for dealing with the problem. This new principle is called matched field noise suppression (MFNS). Based on a previous work of the au-thors group, a full understanding about how a discrete noise source shows effects on the performance of a towed hydro-phone line array has been obtained. In light of that finding, MFNS is proposed, which explores and utilizes the charac-teristics of the noise transmission channel to achieve much greater suppression of the noise in comparison with existing approaches. MFNS combines the concept of matched field processing (MFP) and optimal sensor array processing (OSAP) together to suppress the discrete noise source and to maintain an optimal beam for receiving far-field wanted plane wave signals. A MFNS beam-former is deduced in constraint with signal plane-wave response being unit and noise matched field response being zero. A closed-form solution of the weight vec-tor for the beam-former is given. Computer simulation results agree well to the theoretical analysis.展开更多
This paper proposed a method for blind estimation of underwater channels in shallow water environment by using received data at a single hydrophone or from single beam. First, the received signal is used for source si...This paper proposed a method for blind estimation of underwater channels in shallow water environment by using received data at a single hydrophone or from single beam. First, the received signal is used for source signal reconstruction by means of signal-dependent TF （Time-Frequency） distribution, in association with instantaneous frequency estimation and TF inversion. Then the shallow-water channel estimation is achieved via WRELAX technique by use of the received signal and the estimated source signal. Finally, the results of numerical simulation and experimental test from real data taken in South China Sea trial have proved satisfactory. It is shown that the proposed method is useful for underwater channel estimation.展开更多
The normal mode model for scattering in shallow water is employed to investigate the forward scattering with a target crossing the source-receiver axial line. An experiment was conducted in a littoral environment to a...The normal mode model for scattering in shallow water is employed to investigate the forward scattering with a target crossing the source-receiver axial line. An experiment was conducted in a littoral environment to analyze forward scattering by a slowly moving object. The theoretical and experimental results show that the sound field aberration takes minimum values if the object is located mid-point along the source-receiver line, whereas it attains its maximum if the object is close to the source or receiver. The total field is either enhanced or suppressed if the object crosses different Fresnel zones. In addition, the duration of shad- ow-induced aberration is dependent on the width of the first Fresnel zone, which is longest at the mid-point of the source-receiver line.展开更多
An ensemble Kalman filter（EnKF） approach is proposed to perform sequential tracking of water column sound speed profile（SSP） using a moving acoustic source. First,the SSPs are discretized in depth and range, and a...An ensemble Kalman filter（EnKF） approach is proposed to perform sequential tracking of water column sound speed profile（SSP） using a moving acoustic source. First,the SSPs are discretized in depth and range, and are expressed by the empirical orthogonal functions（EOFs）. Second, the acoustic source state information and the first three orders of EOF coefficients are expressed as the state variable, and the acoustic field information received by the vertical line array are the measured values. Successively, the state variables and measured values are used to establish the state-measure model. Last, the EnKF is utilized to track the state variables. The simulation results show that the root mean square error of SSP and the absolute error of source are all small, and thus the acoustic source tracking-positioning has high accuracy. Moreover, increasing the number of sample collection, the signal-to-noise ratio and the number of receiving elements can improve the tracking-positioning results. The method is verified using the experimental data of the East China Sea.展开更多
The basic principles of target detection by forward acoustic scattering are presented.A direct blast suppression approach based on adaptive filtering(DBS-AF) is proposed to suppress the direct blast.The DBS-AF techniq...The basic principles of target detection by forward acoustic scattering are presented.A direct blast suppression approach based on adaptive filtering(DBS-AF) is proposed to suppress the direct blast.The DBS-AF technique is extended to the linear frequency modulation(LFM) signal,where the envelope of the signal is regarded as a 'general waveform' and imported into the adaptive filter.Application of the DBS-AF method to the data collected from a lake trial yields an output detection curve,in which the direct blast is mapped to the background while the acoustic field aberration is represented by the peak value fluctuation.The inhibitory effect in single hydrophone is approximately- 5 dB,and is then enhanced by exploiting the mean value removal approach as a preprocessing technique.The direct blast is further suppressed to a level of-10 dB by making full use of multichannel receptions.The main factors affecting the algorithm performance are as follows:the fluctuation degree of the receptions during the weighting vector training period and the power ratio of the forward scattered wave to the direct blast when the target is present.展开更多
In this paper a novel method to generate high-precision and continuously adjustable digital time-delay by utilizing the linear phase of a FIR filter is presented. The generated time-delay can be continuously changed b...In this paper a novel method to generate high-precision and continuously adjustable digital time-delay by utilizing the linear phase of a FIR filter is presented. The generated time-delay can be continuously changed by adjusting the filter weights. The time-delay is pre cise and valid for wide-band, while the computational load is low. The proposed approach can find applications in wide-band digital beamforming, adaptive delay estimation, temporal analy sis of reflected waveform, etc.. In the paper, the basic principle, design steps and simulation re sults are given. Also shown are some typical practical applications.展开更多
The signal-to-direct-blast ratio SDRF in acoustic forward-scattering detection can measure the relative magnitudes of the forward scattered wave and the direct-blast,but it does not consider the interference and super...The signal-to-direct-blast ratio SDRF in acoustic forward-scattering detection can measure the relative magnitudes of the forward scattered wave and the direct-blast,but it does not consider the interference and superimposition effects between the two waves.These two waves inevitably interfere with one another and are difficult to distinguish,so it is difficult to directly apply SDRF in target detection and analysis.Based on SDRF and considering the interference between the forward scattered wave and the direct-blast,a new parameter called the acoustic interfered field distortion ΔFTL is developed,and the corresponding calculation formula is deduced.Compared with SDRF,ΔFTL can be obtained directly from data and has the advantage of not relying on prior information to a certain extent.The following is found according to this formula in combination with data from the Qiandao Lake scaled-target detection experiment.(1) Estimating the geometric expansion loss coefficient reveals that the acoustic wave propagates spherically,which is consistent with the simulation results of the ray model based on the measured hydrological parameters.(2) The relation between ΔFTL and the target crossing position is quantitatively confirmed,confirming the effectiveness of the ΔFTL formula.(3) A performance evaluation scheme independent of prior information is established for direct-blast suppression and then applied to an adaptive direct-blast suppression method.The influences of acoustic leakage and disturbances in the attitude angle of the target on the results can be ignored.These results show that ΔFTL can effectively replace SDR_(F),providing theoretical references for conducting performance evaluations on acoustic forward-scattering detection and direct-blast suppression.展开更多
基金The National Natural Science Foundation of China under contract No.11174235the Science and Technology Development Project of Shaanxi Province of China under contract No.2010KJXX-02+2 种基金the Program for New Century Excellent Talents in University of China under contract No. NCET-08-0455the Science and Technology Innovation Foundation of Northwestern Polytechnical University of Chinathe Doctorate Foundation of Northwestern Polytechnical University of China under contract No.CX201226.
文摘Multiple linear regression （MLR） method was applied to quantify the effects of the net heat flux （NHF）, the net freshwater flux （NFF） and the wind stress on the mixed layer depth （MLD） of the South China Sea （SCS） based on the simple ocean data assimilation （SODA） dataset. The spatio-temporal distributions of the MLD, the buoyancy flux （combining the NHF and the NFF） and the wind stress of the SCS were presented. Then using an oceanic vertical mixing model, the MLD after a certain time under the same initial conditions but various pairs of boundary conditions （the three factors） was simulated. Applying the MLR method to the results, regression equations which modeling the relationship between the simulated MLD and the three factors were calculated. The equations indicate that when the NHF was negative, it was the primary driver of the mixed layer deepening; and when the NHF was positive, the wind stress played a more important role than that of the NHF while the NFF had the least effect. When the NHF was positive, the relative quantitative effects of the wind stress, the NHF, and the NFF were about i0, 6 and 2. The above conclusions were applied to explaining the spatio-temporal distributions of the MLD in the SCS and thus proved to be valid.
文摘Discrete noise source suppression in underwa-ter acoustic channel has attracted great attention in recent years. The paper proposes a new principle for dealing with the problem. This new principle is called matched field noise suppression (MFNS). Based on a previous work of the au-thors group, a full understanding about how a discrete noise source shows effects on the performance of a towed hydro-phone line array has been obtained. In light of that finding, MFNS is proposed, which explores and utilizes the charac-teristics of the noise transmission channel to achieve much greater suppression of the noise in comparison with existing approaches. MFNS combines the concept of matched field processing (MFP) and optimal sensor array processing (OSAP) together to suppress the discrete noise source and to maintain an optimal beam for receiving far-field wanted plane wave signals. A MFNS beam-former is deduced in constraint with signal plane-wave response being unit and noise matched field response being zero. A closed-form solution of the weight vec-tor for the beam-former is given. Computer simulation results agree well to the theoretical analysis.
基金This work was supported by the National Natural Science Foundation of China(60472073)(10304015)and by the Doctor Research Foundation of Ministry of Education of China(20020699010)by the Natural Science Fundamental Research Foundation of Shaanxi province(2005F40).
文摘This paper proposed a method for blind estimation of underwater channels in shallow water environment by using received data at a single hydrophone or from single beam. First, the received signal is used for source signal reconstruction by means of signal-dependent TF （Time-Frequency） distribution, in association with instantaneous frequency estimation and TF inversion. Then the shallow-water channel estimation is achieved via WRELAX technique by use of the received signal and the estimated source signal. Finally, the results of numerical simulation and experimental test from real data taken in South China Sea trial have proved satisfactory. It is shown that the proposed method is useful for underwater channel estimation.
基金supported by the National Natural Science Foundation of China(61101192,11174235)the China Postdoctoral Science Foundation(20110491687)+2 种基金the Program for New Century Excellent Talents in University of China(NCET-08-0455)the Science and Technology Development Project of Shaanxi Province(2010KJXX-02)the Foundation of State Key Laboratory on Acoustics(SKLOA201101)
文摘The normal mode model for scattering in shallow water is employed to investigate the forward scattering with a target crossing the source-receiver axial line. An experiment was conducted in a littoral environment to analyze forward scattering by a slowly moving object. The theoretical and experimental results show that the sound field aberration takes minimum values if the object is located mid-point along the source-receiver line, whereas it attains its maximum if the object is close to the source or receiver. The total field is either enhanced or suppressed if the object crosses different Fresnel zones. In addition, the duration of shad- ow-induced aberration is dependent on the width of the first Fresnel zone, which is longest at the mid-point of the source-receiver line.
基金supported by the National Natural Science Foundation of China(11174235)
文摘An ensemble Kalman filter（EnKF） approach is proposed to perform sequential tracking of water column sound speed profile（SSP） using a moving acoustic source. First,the SSPs are discretized in depth and range, and are expressed by the empirical orthogonal functions（EOFs）. Second, the acoustic source state information and the first three orders of EOF coefficients are expressed as the state variable, and the acoustic field information received by the vertical line array are the measured values. Successively, the state variables and measured values are used to establish the state-measure model. Last, the EnKF is utilized to track the state variables. The simulation results show that the root mean square error of SSP and the absolute error of source are all small, and thus the acoustic source tracking-positioning has high accuracy. Moreover, increasing the number of sample collection, the signal-to-noise ratio and the number of receiving elements can improve the tracking-positioning results. The method is verified using the experimental data of the East China Sea.
基金supported by the National Natural Science Foundation of China(11174235,61571366)
文摘The basic principles of target detection by forward acoustic scattering are presented.A direct blast suppression approach based on adaptive filtering(DBS-AF) is proposed to suppress the direct blast.The DBS-AF technique is extended to the linear frequency modulation(LFM) signal,where the envelope of the signal is regarded as a 'general waveform' and imported into the adaptive filter.Application of the DBS-AF method to the data collected from a lake trial yields an output detection curve,in which the direct blast is mapped to the background while the acoustic field aberration is represented by the peak value fluctuation.The inhibitory effect in single hydrophone is approximately- 5 dB,and is then enhanced by exploiting the mean value removal approach as a preprocessing technique.The direct blast is further suppressed to a level of-10 dB by making full use of multichannel receptions.The main factors affecting the algorithm performance are as follows:the fluctuation degree of the receptions during the weighting vector training period and the power ratio of the forward scattered wave to the direct blast when the target is present.
文摘In this paper a novel method to generate high-precision and continuously adjustable digital time-delay by utilizing the linear phase of a FIR filter is presented. The generated time-delay can be continuously changed by adjusting the filter weights. The time-delay is pre cise and valid for wide-band, while the computational load is low. The proposed approach can find applications in wide-band digital beamforming, adaptive delay estimation, temporal analy sis of reflected waveform, etc.. In the paper, the basic principle, design steps and simulation re sults are given. Also shown are some typical practical applications.
基金supported by the National Natural Science Foundation of China(61801275)Shandong Provincial Natural Science Foundation,China(ZR2018BF002)。
文摘The signal-to-direct-blast ratio SDRF in acoustic forward-scattering detection can measure the relative magnitudes of the forward scattered wave and the direct-blast,but it does not consider the interference and superimposition effects between the two waves.These two waves inevitably interfere with one another and are difficult to distinguish,so it is difficult to directly apply SDRF in target detection and analysis.Based on SDRF and considering the interference between the forward scattered wave and the direct-blast,a new parameter called the acoustic interfered field distortion ΔFTL is developed,and the corresponding calculation formula is deduced.Compared with SDRF,ΔFTL can be obtained directly from data and has the advantage of not relying on prior information to a certain extent.The following is found according to this formula in combination with data from the Qiandao Lake scaled-target detection experiment.(1) Estimating the geometric expansion loss coefficient reveals that the acoustic wave propagates spherically,which is consistent with the simulation results of the ray model based on the measured hydrological parameters.(2) The relation between ΔFTL and the target crossing position is quantitatively confirmed,confirming the effectiveness of the ΔFTL formula.(3) A performance evaluation scheme independent of prior information is established for direct-blast suppression and then applied to an adaptive direct-blast suppression method.The influences of acoustic leakage and disturbances in the attitude angle of the target on the results can be ignored.These results show that ΔFTL can effectively replace SDR_(F),providing theoretical references for conducting performance evaluations on acoustic forward-scattering detection and direct-blast suppression.
