浅海舰船噪声声强流的垂直方向性

浅海环境中,确定性声源的多途声信号干涉使得接收点处声强流的方向发生改变,不再与声源位置处的声强流方向一致。只测量声场的标量声强时,无法得到接收点处声强流的垂直方向性,而基于简正波矢量场建模和仿真,可获得理想条件下宽带点声源激发声场声强流的垂直方向性。本文采用单矢量水听器进行海上实验,获得了海洋环境噪声和干扰条件下舰船噪声声强流的垂直方向性。仿真和实验结果表明:远场条件下,浅海干涉现象引起接收点处声强流的方向(极角)随频率和距离变化,其时间-频率分布呈现与LOFAR谱干涉条纹相似的条纹,声强流的极角值主要分布在70?～110?范围内。     

浅海单矢量传感器宽带声源三维定位仿真

针对水平不变的浅海波导中单矢量传感器对低频宽带声源的三维被动定位问题,首先利用平均声强器估计声源方位；其次,通过分离简正模的声压和水平振速分量联合处理获得运动声源相对速度,进一步基于垂直声能流中简正模相干项特征频率不变性以及长时间窗口中多快拍信号的统一处理,建立WARPING变换频谱作为代价函数的搜索处理器,估计该段信号的初始距离,进而获得各时刻声源距离,所提出的方法避免了对拷贝声场和引导声源的依赖；最后,利用多阶简正模相干项与非相干项能量模基处理方法,当声场中存在三阶以上简正模时,可对声源深度进行匹配估计。仿真分析表明,单个矢量传感器能够给出声源的方位、距离及深度估计结果。     

Pekeris波导中简正波的复声强及其应用

在Pekeris波导模型下,关注了简正波的矢量场,讨论了简正波水平复声强和垂直复声强的表述,并分析了其特征.单阶简正波在水平方向是行波,相应的水平复声强仅为有功的;在垂直方向为驻波,相应的垂直复声强仅为无功的.而多阶简正波相互干涉,因此总声场的复声强既有有功分量,也有无功分量,其中只有有功分量参与声能的输运,但无功分量是反映声场信息的重要组成部分.通过对垂直(交互)复声强无功分量和水平交互复声强有功分量的数值分析,对于甚低频率的点源声场,发现当声源深度变化时,上述声场分量的正负号呈有规变化,当接收传感器置 关键词： 目标深度分类 复声强 矢量场 Pekeris波导     

Near fields scattered by an underwater finite cylindrical baffle

In this work,acoustic vector characteristics of near fields scattered by an underwater finite cylindrical baffle are investigated theoretically and experimentally.The analytic expressions for the scattered pressure and particle velocity are derived using the elastic thin shell theory.Calculations are presented for the scattered near fields of the pressure,the particle velocity and the intensity.It is found that the pressure and the particle velocity fields near the surface of the cylindrical baffle are characterized by complex interference structure,particle velocity directions and the source bearings are not consistent.The phase difference between the pressure and the particle velocity is not zero and the intensity vector does not reflect the sound bearings.It can be noted that the distortions of the fields will make the original vector signal processing method based on the free space assumption be no longer applicable in the presence of the cylindrical baffle.These results can serve as a basis of the application for the acoustic vector sensor on board.     

Properties of the acoustic intensity vector field in a shallow water waveguide

Acoustic intensity is a vector quantity described by collocated measurements of acoustic pressure and particle velocity. In an ocean waveguide, the interaction among multipath arrivals of propagating wavefronts manifests unique behavior in the acoustic intensity. The instantaneous intensity, or energy flux, contains two components: a propagating and non-propagating energy flux. The instantaneous intensity is described by the time-dependent complex intensity, where the propagating and non-propagating energy fluxes are modulated by the active and reactive intensity envelopes, respectively. Properties of complex intensity are observed in data collected on a vertical line array during the transverse acoustic variability experiment (TAVEX) that took place in August of 2008, 17 km northeast of the Ieodo ocean research station in the East China Sea, 63 m depth. Parabolic equation (PE) simulations of the TAVEX waveguide supplement the experimental data set and provide a detailed analysis of the spatial structure of the complex intensity. A normalized intensity quantity, the pressure-intensity index, is used to describe features of the complex intensity which have a functional relationship between range and frequency, related to the waveguide invariant. The waveguide invariant is used to describe the spatial structure of intensity in the TAVEX waveguide using data taken at discrete ranges.     

Development of an accelerometer-based underwater acoustic intensity sensor

An underwater acoustic intensity sensor is described. This sensor derives acoustic intensity from simultaneous, co-located measurement of the acoustic pressure and one component of the acoustic particle acceleration vector. The sensor consists of a pressure transducer in the form of a hollow piezoceramic cylinder and a pair of miniature accelerometers mounted inside the cylinder. Since this sensor derives acoustic intensity from measurement of acoustic pressure and acoustic particle acceleration, it is called a p-a intensity probe. The sensor is ballasted to be nearly neutrally buoyant. It is desirable for the accelerometers to measure only the rigid body motion of the assembled probe and for the effective centers of the pressure sensor and accelerometer to be coincident. This is achieved by symmetric disposition of a pair of accelerometers inside the ceramic cylinder. The response of the intensity probe is determined by comparison with a reference hydrophone in a predominantly reactive acoustic field.     

Geoacoustic Inversion Based on a Vector Hydrophone Array

We propose a geoacoustic inversion scheme employing a vector hydrophone array based on the fact that vector hydrophone can provide more acoustic field information than traditional pressure hydrophones. Firstly, the transmission loss of particle velocities is discussed. Secondly, the sediment sound speed is acquired by a matchedfield processing （MFP） procedure, which is the optimization in combination of the pressure field and vertical particle velocity field. Finally, the bottom attenuation is estimated from the transmission loss difference between the vertical particle velocity and the pressure. The inversion method based on the vector hydrophone array mainly has two advantages： One is that the MFP method based on vector field can decrease the uncertain estimation of the sediment sound speed. The other is that the objective function based on the transmission loss difference has good sensitivity to the sediment attenuation and the inverted sediment attenuation is independent of source level. The validity of the inverted parameters is examined by comparison of the numerical results with the experimental data.     

Acoustic vector sensor signal processing

Acoustic vector sensor simultaneously, colocately and directly measures orthogonal components of particle velocity as well as pressure at single point in acoustic field so that is possible to improve performance of traditional underwater acoustic measurement devices or detection systems and extends new ideas for solving practical underwater acoustic engineering problems. Although acoustic vector sensor history of appearing in underwater acoustic area is no long, but with huge and potential military demands, acoustic vector sensor has strong development trend in last decade, it is evolving into a one of important underwater acoustic technology. Under this background, we try to review recent progress in study on acoustic vector sensor signal processing, such as signal detection, DOA estimation, beamforming, and so on.     

On some peculiarities of the energy characteristics of the interference acoustic field in a shallow sea

The results of studies of the scalar and vector energy characteristics of a real acoustic interference field in a shallow sea are presented based on notions of monochromatic fields and common field vector ratios. The importance of the quantities under consideration is that they are the components of the energy-pulse tensor of the acoustic field. The horizontal components of the complex intensity vector are represented only by its real parts, i.e., the imaginary parts of the horizontal components of the intensity vector are equal to zero; the vertical component has both real and imaginary parts. The imaginary part of the vertical component of the complex intensity vector is related to the interference field of acoustic pressure (the potential energy). The energy characteristics of the acoustic field in a shallow sea obtained during a real experiment correspond to the common theoretical field ratios.     

Vector-phase characteristics of acoustic fields: Statistical analysis and measurement algorithms

Statistical characteristics of an acoustic field that are based on the data of simultaneous measurements of pressure and acoustic velocity vector are investigated. Conditions of the formation of vector-phase characteristics of acoustic field are formulated in relation to the dispersion properties of the medium. Crosscorrelation functions of the components of the vector field are presented. Expressions for the characteristic functionals of vector-phase relationships in acoustic fields and, in particular, for the acoustic energy flux are derived with the use of functional methods. Algorithms of space-time processing of the energy flux vector and the optimum measurement algorithm for a Gaussian vector-phase field are considered. The signal-to-noise ratio is determined as the quality index of vector reception algorithms, and its relation to the corresponding parameter of scalar pressure field measurements is revealed. Indices of relative efficiency of vector algorithms are determined depending on the dispersion characteristics of the medium (the flux algorithm) and the dimension of the input vector of observations (the optimum algorithm).     

A passive source ranging method based on the frequency warping transform of the vertical intensity flux in shallow water

The phase of cross-correlation function of two different normal modes contains source range information, which can be extracted by warping transform due to the dispersive characteristics of the shallow water waveguide. The autocorrelation function of the received pressure or particle velocity contains both modal autocorrelation component(MAC) and modal cross-correlation component(MCC), with the former part usually treated as interference for source ranging. Because the real part of the vertical intensity flux(RPVIF) only contains MCC, a passive impulsive source ranging method based on the frequency warping transform of RPVIF with a single vector receiver in shallow water is presented. Using a waveguide-invariant-based frequency warping operator, the cross-correlation components of two different modes in the vertical intensity flux are warped into separable impulsive sequences, the time delays of which are subsequently used for source ranging. The advantages of source ranging based on warping the vertical intensity flux compared with warping the pressure autocorrelation function are pointed out, and the experiment results are also presented.     

Detection of number of sources and DOA estimation based on the combined information processing of pressure and particle velocity using acoustic vector sensor array

In order to solve the problem of DOA(direction of arrival)estimation of underwater remote targets,a novel subspace-decomposition method based on the cross covariance matrix of the pressure and the particle velocity of acoustic vector sensor arrays(AVSA)was proposed. Whereafter,using spatio-temporal virtual tapped-delay-line,a new eigenvector-based criteria of detection of number of sources and of subspace partition is also presented.The theoretical analysis shows that the new source detection and direction finding method is different from existing AVSA based DOA estimation methods using particle velocity information of acoustic vector sensor(AVS)as an independent array element.It is entirely based on the combined information processing of pressure and particle velocity,has better estimation performance than existing methods in isotropic noise field.Computer simulations with data from lake trials demonstrate,the proposed method is effective and obviously outperforms existing methods in resolution and accuracy in the case of low signal-to-noise ratio(SNR).     

噪声源非均匀分布海洋环境噪声水平声能流理论分析

研究水平非均匀分布噪声源所产生的各向异性海洋环境噪声场声能流。提出一种混合型非均匀分布噪声源模型,理论分析并数值计算了此模型情况下的环境噪声场水平声能流。结果表明:非均匀分布噪声源引起的海洋环境噪声场具有显著非零平均水平声能流;不同接收点的水平声能流明显不同;其幅度和方向取决于各个局部海域不等强度声源产生的合成噪声声能流矢量和。研究了两接收点间噪声的声压和振速水平分量、振速水平分量归一化相关系数随两接收点间距的关系,各量之间表现出较强相关性,为分析水下矢量声场目标探测技术性能提供理论依据。      

压差式矢量水听器方位估计中的干扰抵消

矢量水听器由于能获取声场中标量（声压）和矢量（振速）信息，因此单个的矢量水听器就可实现目标方位估计。单个矢量水听器是利用信号的声压和质点振速之间相关性进行信号方位估计，但是当存在干扰，并且干扰和信号之间相关时，如果对运用能量流进行方位估计的方法不加改进，则会出现很大的误差，甚至出现错误的估计。本文提出一种存在已知噪声干扰情况下的干扰抵消方法，并针对该方法进行了仿真试验，最后运用湖试数据进行了验证。结果表明，该方法能有效地减弱相千千柑对信号的影响，实现对信号的方位估计。     

On the angular error of intensity vector based direction of arrival estimation in reverberant sound fields

An acoustic vector sensor provides measurements of both the pressure and particle velocity of a sound field in which it is placed. These measurements are vectorial in nature and can be used for the purpose of source localization. A straightforward approach towards determining the direction of arrival (DOA) utilizes the acoustic intensity vector, which is the product of pressure and particle velocity. The accuracy of an intensity vector based DOA estimator in the presence of noise has been analyzed previously. In this paper, the effects of reverberation upon the accuracy of such a DOA estimator are examined. It is shown that particular realizations of reverberation differ from an ideal isotropically diffuse field, and induce an estimation bias which is dependent upon the room impulse responses (RIRs). The limited knowledge available pertaining the RIRs is expressed statistically by employing the diffuse qualities of reverberation to extend Polack's statistical RIR model. Expressions for evaluating the typical bias magnitude as well as its probability distribution are derived.     

Bi-static sonar applications of intensity processing

Acoustic intensity processing of signals from directional sonobuoy acoustic subsystems is used to enhance the detection of submerged bodies in bi-static sonar applications. In some directions, the scattered signals may be completely dominated by the incident blast from the source, depending upon the geometry, making the object undetectable by traditional pressure measurements. Previous theoretical derivations suggest that acoustic vector intensity sensors, and the associated intensity processing, are a potential solution to this problem. Deep water experiments conducted at Lake Pend Oreille in northern Idaho are described. A large, hollow cylindrical body is located between a source and a number of SSQ-53D sonobuoys positioned from 5 to 30 body lengths away from the scattering body. Measurements show changes in the acoustic pressure of less than 0.5 dB when the scattering body is inserted in the field. However, the phase of the acoustic intensity component formed between the acoustic pressure and particle velocity component orthogonal to the direction of incident wave propagation varies by as much as 55 degrees. This metric is shown to be a repeatable and strong indicator of the presence of the scattering body.     

矢量拖线阵水听器流噪声响应特性

针对传统拖线阵流噪声理论的局限性, 建立了完善的矢量拖线阵流噪声理论分析方法, 可全面准确地揭示矢量拖线阵流噪声响应特性. 基于细长圆柱的湍流边界层压力起伏Carpenter模型, 采用波数-频率谱分析方法对矢量拖线阵流噪声响应特性进行了理论研究, 导出了圆柱形矢量水听器流噪声响应的声压和振速自功率谱及其互功率谱的解析表达式, 定量分析了流噪声响应功率谱与拖曳速度、水听器尺寸、套管尺寸和材料等参数之间变化规律; 另外, 还讨论了圆柱形矢量水听器偏离护套轴线时矢量拖线阵流噪声响应, 导出了流噪声响应的声压、径向和轴向振速自功率谱及其互功率谱的解析表达式, 数值计算结果表明: 轴线偏移距离对声压和轴向振速的高频噪声的影响要大于对低频噪声的影响, 而对径向振速的全频段噪声都有明显影响, 且对振速分量影响要远大于对声压影响.     

Measurement of acoustic particle velocities in enclosed sound field: Assessment of two Laser Doppler Velocimetry measuring systems

The performances of two Laser Doppler Velocimetry (LDV) systems adapted for measuring the acoustic particle velocities are assessed in enclosed sound field. This assessment is performed by comparing the acoustic velocities measured by means of LDV to reference acoustic velocities estimated from sound pressure measurements. The two LDV systems are based on a single optical bench which delivers an optical signal called Doppler signal. The Doppler signal, which is frequency modulated, is analyzed by means of two signal processing systems, the BSA (Burst Spectrum Analyser from Dantec) on the one hand, and a system specifically developed for the estimation of the acoustic velocity on the other hand. Once the experimental setup has been optimized for minimizing the errors made on the reference velocities, the assessment is performed and shows that both systems can measure the acoustic velocity in enclosed field in two the frequency ranges [0-4 kHz] and [0-2 kHz] respectively for acoustic velocity amplitudes of 10 mm/s and 1 mm/s.     

Optimal acoustic fields in compact thermoacoustic refrigerators

Thermoacoustic refrigerators have been developed during the last 15 years, employing quasi-standing resonant acoustic waves inside fluid-filled cavities to transfer heat along a stack region. Because higher efficiency can be reached when a significant travelling wave component exists in the resonator, specific resonant thermoacoustic devices have been designed allowing to adjust more or less the ratio of travelling and standing wave components. However, the acoustic pressure field and the particle velocity field do not appear to be the optimal ones, for the thermal quantities of interest. Thus, it is the aim of the paper to present a new kind of thermoacoustic standing wave-like device which allows to control easily and independently the pressure field and the particle velocity field, after investigating the optimal acoustic field, in the stack region, for the main parameters of interest, i.e. the temperature gradient, the thermoacoustic heat flow and the coefficient of performance.     

Delay and Doppler spreads in underwater acoustic particle velocity channels

Signal processing and communication in acoustic particle velocity channels using vector sensors are of interest in the underwater medium. Due to the presence of multiple propagation paths, a mobile receiver collects the signal with different delays and Doppler shifts. This introduces certain delay and Doppler spreads in particle velocity channels. In this paper, these channel spreads are characterized using the zero-crossing rates of channel responses in frequency and time domain. Useful expressions for delay and Doppler spreads are derived in terms of the key channel parameters mean angle of arrival and angle spread. These results are needed for design and performance prediction of systems that utilize underwater acoustic particle velocity and pressure channels.