一种基于单水听器的浅海水下声源被动测距方法

针对浅海波导中宽带脉冲声源的被动测距问题,本文在群延迟理论的基础上,与warping变换处理相结合,提出了一种适用于浅海波导中宽带声源的单水听器被动测距方法.利用warping变换可以实现对脉冲声源接收信号各阶简正波的分离提取,对分离后的简正波进行时频分析处理可以得到各阶简正波到达时刻和频率之间的关系,即各阶简正波的频散曲线,从而得到任意两阶简正波到达接收水听器的时延差.海底相移参数P是描述海底地声参数的一个重要参量,包含了海底地声参数信息,在海底环境参数未知而P已知的情况下,利用P和简正波水平波数之间的关系可以求得任意两阶简正波的?S_(g,mn)(群慢差).根据群延迟理论,利用得到的任意两阶简正波的时延和?S_(g,mn)可实现利用单水听器对水下声源进行被动测距.本文提出的测距方法测量简单、计算方便,具有较强的实用意义.数值仿真和海上实验数据处理结果的测距误差都在10%以内,证明了该方法的有效性.     

水平阵信号压缩感知用于简正波分离

针对水平阵信号简正波分离过程中常规波束形成分辨率低以及warping模态滤波不适用于复杂声信号的问题,提出水平阵信号压缩感知用于简正波分离的方法。利用压缩感知在方位估计中的高分辨特性,通过估计水平阵接收信号在频率方位角上的二维分布,分离得到各阶简正波的方位谱,并逆Fourier变换得到时域波形。仿真孔径1 km、阵元间隔10 m水平阵接收20~200 Hz伪随机声信号和脉冲声信号,所提方法分离出的各阶简正波与理论波形的相关系数在0.97~1.0。对2011年北黄海声学实验中的海底28元水平阵接收的气枪信号,在合成至1 km孔径后使用压缩感知方法分离简正波,其与warping模态滤波分离得的前5阶简正波相关系数在0.82~0.93。仿真与实验都说明了水平阵信号压缩感知简正波分离方法的有效性。      

一种基于模态匹配的浅海波导中宽带脉冲声源的被动测距方法

针对浅海波导中宽带脉冲声源的被动测距问题,本文在模态匹配和匹配场处理定位方法的基础上,提出了一种适用于具有液态半无限空间海底的浅海波导中声源的单水听器被动测距方法.利用warping变换可以对脉冲声源接收信号的各阶简正波实现有效分离,由此得到各阶简正波的频域信号.海底相移参数是描述海底地声参数的一个重要参量,包含了海底地声参数信息,而各阶简正波的水平波数可以通过含有海底相移参数的表达式来表达.此外,由于声速剖面对简正波的各阶水平波数具有相近的影响,因此通过对任意两阶简正波进行联合处理,可以近似消除声速剖面对简正波水平波数差的影响.任意两阶简正波的水平波数差只近似用于海底相移参数、海深以及波导中平均声速三个参数有关,可以简单、快速地计算相应拷贝场,然后通过建立代价函数并对简正波模态进行匹配,可以实现对水下脉冲声源的被动测距.与传统的模态匹配定位方法相比,本文提出的方法既不需要使用水听器阵,又可以简单、快速地计算出拷贝场.数值仿真和海上实验数据处理结果的测距误差都在10%以内,证明了该方法的有效性.     

反演声场简正波耦合系数矩阵

研究了有内波传播时声场的耦合简正波形式,分析表明各阶简正波系数的时间信号包含多个频率成分,各成分的频率为对应的两地波数差与内波速度的乘积,各频率成分的振幅与对应简正波之间的耦合系数成正比。因此即使内波的波形不随其传播而变化,接收器处的各阶简正波系数仍然具有多频的复杂结构。由此并根据简正波耦合强度与声场简正波系数起伏强度的对应关系提出了一种反演简正波耦合系数矩阵的方法;并用实验中获得的内波数据,反演了声场;计算结果表明:该方法有效地反演了内波传播情况下的简正波耦合系数矩阵。     

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.     

空气中快速运动声源水下声场的波数积分模型

本文采用二维波数积分，对空气中高速运动声源激发的水下声场进行建模。针对二维波数积分计算声场时域解计算量大的问题，提出一种快速计算方法。用本文提出的方法，对深海和浅海情况下，空气中高速运动单频点声源激发的水下声场进行了计算和仿真。计算结果表明：在深海，水下接收信号的幅度和瞬时频率随时间发生变化；接收器深度、接收器与声源运动轨迹的最小距离对接收信号的变化快慢有较大影响，而声源高度的影响较小；在浅海中，接收信号呈现快速的幅度起伏，明显的多普勒频移和大的频率展宽效应。与简正波方法相比，本文方法主要适用于近场计算，而简正波方法适用于远场。另外，当声源频率较高时，二维波数积分方法的计算量将迅速增大。     

浅海中运动声源径向速度与距离的无源估计

针对浅海波导中声源距离的无源估计问题,提出了一种环境参数和声场模型无关的、不依赖于引导声源的运动声源径向速度以及距离估计方法。该方法首先通过双水听器低频声场强度距离波数谱变换(R-K)的相位差获得干涉简正波水平波数,对水平波数轴定标来估计运动声源的径向速度。进一步地,对接收信号自相关函数进行WARPING变换得到运动声源距离的无源估计。对于反射类简正波为主的声场,在某一假定距离下根据某两时刻接收信号WARPING变换后干涉简正波谱峰频率与假定距离的关系估计距离;对于反射类或折射类简正波为主的声场,根据两个时刻接收信号的β-WARPING变换后干涉简正波的脉冲时延估计距离的值。数值仿真分析了等声速、负梯度以及温跃层3种水文环境下的噪声以及环境宽容性,结果表明径向速度与距离的估计不依赖于环境参数。利用2005年北黄海实验数据验证了方法的可行性,径向速度与距离的估计值与实际值符合良好。      

利用自相关函数warping变换的浅海声源深度判别

针对浅海波导声源深度判别问题,提出了一种利用warping变换提取接收信号简正波相关项的深度判别方法。对接收信号自相关函数做warping变换,分离其简正波相关项,利用能量占主导的简正波相关项特征频率之间的比例关系,确定其号数,从而分辨水面声源和水下声源。公式推导和数值仿真结果说明:不同深度声源激发的能量占主导的简正波相关项特征频率不同,可以用于判别声源深度。海试实验结果证明:在海水声速随深度不变或缓变的水文环境,低频条件下,该方法可以分离简正波相关项并确定其号数,在未知声源距离的情况下有效进行声源深度判别,且无须声源相对接收器运动。      

浅海中利用单水听器的声源被动测距

针对浅海声波导中远距离脉冲声源被动测距问题,提出了一种利用单水听器接收信号自相关函数进行warping变换的声源被动测距方法。理想水下声波导中,接收信号warping变换输出的傅里叶变换频谱中具有不变性频率特征,即与声源距离无关的各简正波截止频率;信号自相关函数中不同简正波相干成分也存在不变性频率特征;推导了未知声源距离时特征频率提取值与不变性频率特征之间的近似关系式。这些规律可推广到实际浅海声波导,并用于声源被动测距。利用声场计算模型来提供具有不变性频率特征的频谱,对2011年12月北黄海海域水声实验中单水听器接收的脉冲声数据进行了处理,验证了方法的有效性,测距结果和实际距离符合良好,平均测距误差在10%以内。      

利用简正波频散特征映射方法进行海洋环境参数反演

浅海波导中传播的脉冲信号可以通过频散特征映射方法(warping变换)进行简正波的有效分离,这使得频散曲线的获取更加容易和准确.利用简正波频散特征映射方法分析2010年南海声层析实验中单个阵元接收的声学信号,有效分离出各号简正波,并进一步通过Wigner-Ville分布处理提取出波导中各号简正波的频散曲线.将提取的频散曲线与理论计算到达时差进行匹配,实现了利用单水听器信号的海洋环境参数反演.实验结果表明:将简正波分离与Wigner-Ville分布相结合可有效消除Wigner-Ville分布在估计多分量信号时的交叉干扰,提取的频散特征可很好地用于同时反演海水和海底声速剖面。为评价反演结果的有效性,对反演结果进行了后验概率分析,并将一小时内的海水声速剖面反演结果与温度链实测值作对比,二者符合较好.      

Method for the distinguish of normal modes in shallow water under near field

This paper proposes a method to distinguish the normal modes in shallow water under near field.The method,which is based on frequency-wavenumber(F-K) transform,employs the 2D matrix comprising near field horizontal multi-channel signals.These signals are transformed from the time-space domain to the frequency-wavenumber domain,and the normal modes in the signals are distinguished by extracting the wavenumbers component at each frequency for each order in the frequency-wavenumber domain.The practical reliability and validity of this method are verified by performing numerical simulation and a tank experiment,and the results showed that the normal modes in the Pekeris waveguide below 200 Hz could be obtained reliably at 500 m by using this method.     

高功率微波照射下半空间上方天线罩耦合特性

利用两次傅里叶变换得到半空间界面的反射波后,将直接入射波和界面反射波两个时域脉冲源通过等效原理引入到包含目标的时域有限差分(FDTD)的计算域中。计算了高功率微波入射情形下,改变入射面、极化方式时天线罩内部观察点的能流密度的变化,并总结其规律。数值算例表明,对于贴近地面的目标来讲,半空间的反射波会给目标内部带来新的能量冲击。该方法可以用于计算目标内部耦合近场及功率密度。     

Transforming and separating rotating disk vibrations using a sensor array

This paper presents a method to separate the complex vibration pattern of a rotating disk into simpler entities. The decomposition transforms data measured by an array of sensors into time domain signals representing the contribution of individual modes of vibration. Having performed the decomposition with respect to wavelength, speed and direction of travel, the obtained measurements can be projected onto a rotating body experiencing variable rotational speed relative to the sensors. Unlike previous works, the vibrations here are decomposed into time domain signals that provide better insight into stress levels and fatigue than frequency domain based decompositions. Furthermore, the proposed method works under non-stationary conditions, e.g. under rapid angular acceleration and during transient motions. By exploiting the spatial deployment of sensors, the proposed transformation can produce information about the deformations in the body-fixed or material coordinates which is essential for stress analysis. The main feature of the method is the ability to separate modes of vibration that normally overlap in the frequency domain, to enable better insight into the sources of vibration. The method is demonstrated by analytical, numerical and experimental examples.     

基于自适应无参经验小波变换和选择集成分类模型的运动想象

运动想象模式识别率的提高对脑机接口(BCI)技术的应用具有重要意义,本文采用自适应无参经验小波变换(APEWT)和选择集成分类模型相结合的方法提高脑电(EEG)信号的分类识别准确率.首先,通过APEWT将EEG信号分解成不同的模态;然后,使用最优模态重构后的信号计算其能量谱(ES)特征,使用最优模态分量计算其边际谱(MS)特征;最后,将不同时间段的ES特征和不同频段的MS特征输入到构建的选择集成分类模型中,从而得到其分类结果,并将该方法与其他4种组合方法进行比较.实验结果表明,本文方法具有较好分类准确率和实时性,其平均分类正确率高于其他4种方法,同时较近期使用相同数据的文献也有优势.本文为在线运动想象类BCI的应用提供了新的方法和思路.     

Least squares approach in wavenumber domain for sound field recording and reproduction using multiple parallel linear arrays

A novel signal processing method is proposed for sound field recording and reproduction using multiple parallel linear microphone and loudspeaker arrays. In sound field recording and reproduction, the problem is how to calculate the transfer filters that transform the signals recorded by microphones into the driving signals of the loudspeakers. The proposed method is based on the spatial Fourier transform in the horizontal angle combined with the least squares (LS) approach in the elevation angle. In the proposed method, the signals recorded by each linear microphone array and those that drive each loudspeaker array are decomposed into the wavenumber domain by the spatial Fourier transform in the horizontal direction. The transfer filters are then calculated by the LS approach in the wavenumber domain. As a result, the size of the matrix of each transfer function in the wavenumber domain is much smaller than that of the conventional LS approach in the temporal frequency domain (LSTF), and well-conditioned stable transfer filters can be obtained with low computational cost without regularization. Computer simulation results show that the proposed method reconstructed a sound field around the control points as accurately as the conventional LSTF.     

基于连续小波变换的简正波检测与提取技术

宽带声源在远距离传播中的频散过程反映着海洋环境特性的重要信息,准确提取这一过程中各简正波的有关信息是有效实现海洋声场反演的重要前提。小波变换虽然已被用于获取宽带声源的时频分布,但不具备适用于不同信号的柔性。在此背景下,本文介绍了一种自适应基小波方法,可适应不同形式的爆炸声信号,从而有效实现了频散现象的获取。在此基础上,本文同时建立了各号简正波的重构方法,经仿真测试,重构出的简正波与实际波形几乎相同。     

High-resolution NMR with resistive and hybrid magnets: deconvolution using a field-fluctuation signal

A method for compensating effect of field fluctuation is examined to attain high-resolution NMR spectra with resistive and hybrid magnets. In this method, time dependence of electromotive force induced for a pickup coil attached near a sample is measured synchronously with acquisition of NMR. Observed voltage across the pickup coil is converted to field fluctuation data, which is used to deconvolute NMR signals. The feasibility of the method is studied by (79)Br MAS NMR of KBr under a 30T magnetic field of a hybrid magnet. Twenty single-scan NMR signals were accumulated after the manipulation, resulting in a high-resolution NMR spectrum.     

Mode separation of Lamb waves based on dispersion compensation method

Ultrasonic Lamb modes typically propagate as a combination of multiple dispersive wave packets. Frequency components of each mode distribute widely in time domain due to dispersion and it is very challenging to separate individual modes by traditional signal processing methods. In the present study, a method of dispersion compensation is proposed for the purpose of mode separation. This numerical method compensates, i.e., compresses, the individual dispersive waveforms into temporal pulses, which thereby become nearly un-overlapped in time and frequency and can thus be extracted individually by rectangular time windows. It was further illustrated that the dispersion compensation also provided a method for predicting the plate thickness. Finally, based on reversibility of the numerical compensation method, an artificial dispersion technique was used to restore the original waveform of each mode from the separated compensated pulse. Performances of the compensation separation techniques were evaluated by processing synthetic and experimental signals which consisted of multiple Lamb modes with high dispersion. Individual modes were extracted with good accordance with the original waveforms and theoretical predictions.