消频散阵不变量距离估计方法

针对传统阵不变量方法在低信噪比和远距离测距性能差的问题,提出了消频散阵不变量测距方法。该方法首先对垂直阵接收信号进行消频散波束形成,消除频散影响,压缩脉冲宽度,提高简正波到达时间分辨率;然后,对得到的角度-时间谱采用反卷积处理提高简正波俯仰角度分辨率。通过消频散和反卷积处理,减小了简正波相对到达时间和俯仰角在角度-时间谱图中的聚焦范围,有利于准确的提取阵不变量和估计目标声源的距离。计算机仿真证明了该方法在低信噪比条件下的鲁棒性;2009年崂山湾实验数据处理结果表明:相比于传统阵不变量测距方法,该方法距离估计误差减小2.5%。     

利用阵不变量的浅海宽带声源距离深度估计方法

现有阵不变量方法未能确定声源深度,且通常对远距离声源的测距误差较大。针对这一问题,提出一种利用阵不变量的宽带声源距离深度估计方法。该方法先对宽带接收信号进行频域波束形成和傅里叶逆变换,转换到波束-时间域以实现模态分离,波束-时间域各峰值位置的连线形成波束时间迁移曲线,曲线形状由阵不变量参数决定且与声源距离相关,曲线上能量分布由各阶模态激励决定且与声源深度有关;再沿波束时间迁移曲线提取波束时间强度并进行匹配处理,最终实现声源距离深度估计。SWellEx-96实验数据处理结果表明,本文所提方法的声源距离和深度估计平均相对误差分别为3.9%和3.4%,而常规阵不变量方法的平均相对测距误差为5.1%,验证了所提方法的优越性能。     

水下目标被动测距的一种新方法:利用波导不变量提取目标距离信息

水声学中波导不变量的研究是近30年来引人注目的课题之一。水下目标辐射噪声的直达波和海面、海底反射波之间的干涉现象中隐含有下水目标的距离信息。提取这种距离信息就为水下目标的被动测距提供了一种新的途径。理论分析和实际海试都证明,甚至单水听器的LOFAR(Low Frequency Analysis Record)图都隐含着目标的距离和运动信息。本文给出利用波导不变量提取目标距离信息的理论推导,证明了在形成干涉条纹的外界条件具备时,利用多个水听器构成的基阵也能以较大增益提供目标距离信息。虽然组成基阵的每一水听器出现干涉条纹的条件是有差异的。这种差异在波束成形时可以加以利用和补偿。本文提出的理论和部分仿真、海试结果为水下目标被动测距和目标识别提供了一种新的途径。      

一种基于β-warping变换算子的被动声源距离估计方法

基于浅海简正波水平波数差与波导不变量之间的关系, 本文提出了一种适用于水平不变浅海声波导中接收信号自相关函数的频域卷绕变换算子. 该算子可以将接收信号自相关函数中的简正波互相关成分变换为时域上可分离的脉冲序列, 且脉冲序列的相对延迟时间包含声源距离信息. 利用已知距离的引导声源, 由单水听器记录的脉冲信号即可实现被动声源距离估计. 对仿真和实验获得的脉冲信号数据处理结果验证了该变换算子用于被动声源距离估计的有效性.     

基于波导不变量的目标运动参数估计及被动测距

结合波导不变量的概念推导了中近程目标的干涉条纹方程,它表明在浅海声场中此干涉条纹为一族类双曲线。采用Hough变换对LOFAR图和方位-时间历程进行处理,可以估计反映环境信息的波导不变量β、航向角φ以及最近通过距离和航速比r₀/v。仿真研究和海试数据分析均表明,低频声场确实存在稳定的干涉结构,结合图像处理手段进行参数估计有较高的估计精度。基于双阵元模型可以进行被动测距,仿真研究表明该算法有较高的定位精度和较好的稳健性。     

一种基于简正波模态消频散变换的声源距离深度估计方法

针对浅海环境中传播的低频宽带水声脉冲信号,基于简正波水平波数差和波导不变量之间的关系,本文提出了一种利用距离-频散参数二维平面聚焦测距与匹配模态能量定深的目标声源定位方法.首先,通过将由频散参数和波导不变量表示的前几阶模态相速度与由环境模型计算的相速度进行对比分析,从而估计出前几阶模态的频散参数和环境的波导不变量.其次,利用估计出的频散参数值和波导不变量对接收信号进行消频散变换处理,只有当接收信号的距离参数等于目标声源距离时,各号简正波的幅度均达到最大值,在距离-频散参数二维平面上,出现声压聚焦的现象,利用此现象可以估计目标声源的距离.不仅如此,消频散变换后的接收信号,前几阶模态在时域上明显地分离开来,可以准确地估计出前几阶模态的能量,采用多模态能量匹配的方式,可以估计出目标声源的深度.最后,通过对仿真和冬季获得的气枪信号数据处理结果验证了本文方法的有效性.     

用子空间旋转不变法同时估计水下多目标的距离和方位

提出了一种可在单次回波内同时完成方位和时延估计的高分辨新方法,它采用于空间旋转不变法(ESPMT方法)的思路构造两个子阵,通过对其自相关矩阵和互相关矩阵的广义特征分解,用特征值估计多目标方位,用特征向量估计多目标时延,利用特征值和特征矢量的对应关系自动实现方位和时延参数的配对.计算机仿真结果表明,该方法的分辨能力、估计精度和正确配对概率都优于常规方法,较好地实现了水下多目标距离和方位的同时估计及配对,进而可对多目标进行定位.     

Waveguide invariant estimation in elastic Pekeris waveguide

Focus on sound intensity,particle velocity,complex sound intensity and waveguide impedance,the formation mechanism of interference structures in range-frequency domain for the above four kinds of physical quantities in Pekeris waveguides is analyzed based on Normal Mode Theory.Also,a sea-trial with broadband radiated source is conducted to verify the analysis results.Both the simulation results and the analysis of sea-trial data indicate that,in range-frequency domain,the four kinds of physical quantities will exhibit a stable interference structure which can be expressed with waveguide invariant β.Among these quantities,the coherent components of complex sound intensity can better reflect the interference characteristics of the waveguide.Finally,a multi-scale linear filter is introduced to deal with the sea-trial LOFAR(Low Frequency Analysis Recording) spectrum,the processing results show that the proposed filter can effectively enhance the interference characteristics in images,and conductively detect and extract striations' information from interference structures in LOFAR spectrum.     

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.     

Near-field acoustic intensity measurements using an accelerometer-based underwater intensity vector sensor

An accelerometer-based underwater acoustic intensity vector sensor is used to measure the acoustic nearfield of a single spherical source, and a pair of sources that vibrate in or out of phase with each other. The intensity sensor consists of co-located pressure and inertial sensors within a neutrally buoyant probe body. The design of this probe has been published previously. The measurements were performed in a large tank at a frequency of 5 kHz for two sources of different sizes, corresponding to ka values of 0.7 and 1.2 respectively, where k is acoustic wavenumber and a is the source radius. By way of validation, the acoustic intensity field from two closely spaced, interacting spherical radiators is predicted using the exact theory of the translational addition theorem for spherical wave functions. The predictions using this theory compare favorably well with the measured intensity field. Beam pattern and calibration data obtained for the intensity sensor suggest that underwater acoustic intensity generated by simple and complex sources can be measured to an accuracy of ±1 dB provided that ka is less than approximately 0.2.     

Robust passive range estimation using the waveguide invariant

The waveguide invariant principle is used to estimate the range to a broadband acoustic source in a shallow-water waveguide using a single acoustic receiver towed along a path directly toward the acoustic source. A relationship between the signal processing parameters and the ocean-acoustic environmental parameters is used to increase the effective signal-to-noise ratio without requiring detailed knowledge of the environment. Heuristics are developed to estimate the minimum source bandwidth and minimum horizontal aperture required for range estimation. A range estimation algorithm is tested on experimental and simulated data for source ranges of 500-2200 m and frequencies from 350 to 700 Hz. The algorithm is accurate to within approximately 25% for the cases tested and requires only a minimal amount of a priori environmental knowledge.     

On fast estimation of direction of arrival for underwater acoustic target based on sparse Bayesian learning

The Direction of Arrival(DOA) estimation methods for underwater acoustic target using Temporally Multiple Sparse Bayesian Learning(TMSBL) as the reconstructing algorithm have the disadvantage of slow computing speed.To solve this problem,a fast underwater acoustic target direction of arrival estimation was proposed.Analyzing the model characteristics of block-sparse Bayesian learning framework for DOA estimation,an algorithm was proposed to obtain the value of core hyper-parameter through MacKay's fixed-point method to estimate the DOA.By this process,it will spend less time for computation and provide more superior recovery performance than TMSBL algorithm.Simulation results verified the feasibiUty and effectiveness of the proposed algorithm.     

水声多输入多输出信道的分布式压缩感知估计

多输入多输出技术通过采用多个阵元进行多发多收空间复用信道可在极其有限的通信带宽下实现高速水声通信,但由于同时存在通道间干扰和多径干扰,水声MIMO信道估计变得困难。提出利用MIMO水声信道多径稀疏结构存在的相关性,在经典联合稀疏模型的基础上对MIMO观测矩阵进行重组,从而建立基于分布式压缩感知的单载波水声MIMO通信信道联合稀疏模型;同时,针对信道响应中具有相同多径位置的稀疏部分和特有稀疏部分设计区分性正交匹配追踪算法进行联合重构,进一步抑制通道间干扰的影响。最后通过仿真和海上实验进行本方法有效性的验证,实现16 kbps的MIMO水声通信。通过算法推导、仿真和实验可得到结论:利用MIMO水声信道多径相关性进行分布式压缩感知估计可提高估计性能。     

Numerical prediction of envelope line-spectrum intensity in underwater acoustic waveguides

In order to predict the detectible range and region of passive sonar in underwater channel,the attenuation causes of envelope line-spectrum height during vessel noise propagation are analyzed and an approach of numerical prediction is proposed.In the paper a model for vessel radiated noise is established by a periodically locally stationary random process,two formulae of the envelope line-spectrum height with and without background-noise are deduced, therefore the attenuation rule of the envelope line-spectrum height is obtained.It is shown that the transmission loss of the sound level of the envelope line-spectrum is same as the sound level of the stationary spectrum,but the decrease of envelope line-spectrum height depends on a modified scale of amplitude modulation depth which is variable with the ratio of signal to noise. An approach of numerical prediction for envelope line-spectrum height is as follows:first,the transmission loss of the stationary radiated noise is derived using the numerical approaches of normal modes or wavenumber integration or PE etc.,then the ratio of signal to noise on sound field is calculated,finally the decrease of envelope line-spectrum height is obtained according to the modified scale,and the envelope line-spectrum height in sound field is predicted.The theory and the numerical prediction approach possess certain innovation,practicality,simplicity and suitability for engineering.     

浅海运动目标波束域波导不变量测距方法研究

波导不变量是描述海洋波导环境声信号水平距离与频率干涉结构现象的特征参量。运动目标波导不变量测距方法需要已知目标速度值,运动目标速度一般是未知的。针对这一问题,本文提出了一种利用水平线阵估计目标运动速度的浅海波导不变量测距方法。该方法通过不同时刻波束域声信号互谱分析进行声源速度估计,结合HOUGH变换提取的LOFAR图斜率和波导不变量进行运动目标测距。仿真结果表明,该方法能够有效的进行运动目标的距离估计。利用2013年7月浅海实验数据,该方法估计出了发射船的距离,并与GPS测量的距离进行对比,相对误差小于10%。     

Reference-less acoustic holography techniques based on sound intensity

This paper describes a detailed implementation and application of the intensity-based holography method called BAHIM, and it investigates its possibilities and its limitations. Although this method is attractive in the sense that it bypasses the reference signal requirement, i.e., one of the main difficulties of the classical near-field acoustic holography, its degree of accuracy does not appear to be adequate. This constraint has consequently led to the development of another method called CIBNAH, based on complex intensity, as an alternative. This novel approach provides additional accuracy in detecting and localizing sources and good compatibility, in form and amplitude, with NAH results.     

一种快速水声目标波达方向估计方法

以基追踪为重构算法的水声目标波达方向估计方法在实际的应用中往往运算速度较慢,针对这一问题,在分析水声目标空间稀疏特性的基础上,结合压缩感知理论框架下波达方向估计的特点,提出一种快速水声目标波达方向估计方法。该方法通过逐步减小逼近参数的方式来得到l₀范数最优解,实现水声目标信号的波达方向估计。通过计算机仿真从成功率、运算时间、分辨角度等多个方面与基追踪算法进行比较分析,实验表明:在成功率和分辨角度上所提出算法与基追踪算法性能相当,但运算时间却仅仅是基追踪算法的1/11。