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.     

浅海大孔径水平阵列频移补偿定位方法

浅海波导中简正波干涉使得声场水平相关随距离出现振荡,利用声信号水平距离-频率干涉规律推导了不同阵元接收信号间的频移补偿关系式,结合大孔径阵列阵元空间分布离散度高的特点提出适用于声源频谱缓变信号的定位方法。利用频移补偿量随声源位置的变化,将两两阵元组合输出的模糊度平面叠加实现水平二维平面定位。仿真结果表明方法定位性能良好,对环境参数失配宽容性好。频移补偿后的线性相位关系有效提高了接收信号间的相关性,进而提升大孔径阵列的处理增益。阵列的孔径优势提高了空间分辨能力,模糊度平面峰值-背景比高。海试数据验证表明, 10～80 km测距结果平均相对偏差为5.68%,二维平面内定位结果平均距离偏差为0.78 km。     

不同频段下利用虚拟接收方法的声源测距性能分析

考虑到传统的匹配场处理定位需要复杂的匹配声场计算,并对环境参数和声场模型有很高的依赖,为了克服这种缺点,采用虚拟接收方法对声源进行测距。首先对垂直阵接收到的引导声源和目标声源的信号进行相关处理,得到虚拟接收声场并估计虚拟接收声场干涉条纹的斜率,结合波导不变特征量β对目标声源进行测距。通过数值仿真和2004年南海实验数据处理,讨论了浅海斜坡海域环境中不同频段下利用虚拟接收方法对宽带声源测距的性能。随着频率升高,需要展宽频带以获得完整的干涉条纹和良好的测距结果。在实验数据处理中,选取频段较高的信号时,由于阵列间距偏大不能保证采样的简正波模式的正交归一特性,不能获得正确的测距结果。      

多输入多输出与时反联合的波导声呐有源目标定位

为了提高对浅海静止小目标的探测能力,提出了将多输入多输出和时反处理相结合的波导声呐处理框架。利用收发合置垂直阵,假设目标为点目标,每一个阵元轮流时反发射正交信号照射目标,整个阵接收对应的目标回波。当所有的阵元发射正交信号结束以后,对所有接收的目标回波数据进行分集处理,然后与时反发射驾驶向量做匹配滤波完成对目标的定位。分时发射策略克服了水声信道时延扩展和多普勒扩展导致常规多输入多输出处理接收端不同回波信号分离的困难。采用物理时反发射和数值时反接收聚焦,有助于抑制混响、提高回混比。数值仿真和波导水池实验结果表明多输入多输出时反处理较常规的有源匹配场处理以更高的精度对波导中的目标进行定位。      

非均匀波导中的声聚焦

理论研究了声波在非均匀波导中的空间聚焦问题,利用多模态导纳法构建波导内任意位置处声压与入射声压在模态域的映射关系,计算使声波聚焦于空间某位置时的最佳入射波,并画出了相应的聚焦声场.研究了三种非均匀情况:水平变截面波导、含散射体波导以及声速垂直变化波导.结果表明,当输入最佳入射波时,在非均匀波导中可以产生良好的单点或多点声聚焦效果,声波的聚焦过程充分地利用了波导结构及介质非均匀性对声波的散射作用.     

基于压缩拷贝场向量的空域滤波器设计

近几十年来,匹配场处理技术得到了广泛深入的研究,并针对实际应用提出了一系列的具体处理算法.当感兴趣的水下目标信号被水面强干扰信号掩蔽时,对水下目标的匹配场处理定位性能显著下降.现有的广义空域滤波器可以抑制水面强干扰,但计算速度较慢并且内存消耗较大.提出了一种基于压缩拷贝场算法的空域滤波器设计方案,并通过非相干叠加处理宽带问题.相对于现有的空域滤波器,当接收阵元数N大于波导中有效简正波号数Q时,该滤波器可以大幅度缩减计算时间、节约运行内存,并且保持了对水面强干扰的抑制性能.针对近岸浅海环境进行了仿真计算,并给出了一些近岸浅海海域试验数据处理结果,验证了该空域滤波器的性能和对计算速度的提升.结果表明,应用基于压缩拷贝向量的矩阵滤波器对强干扰下的弱目标进行宽带非相干匹配场定位,可实现水下目标的有效区分.     

虚拟接收目标定位技术中引导声源对目标声源的信噪比补偿

目标声源的低信噪比是目标定位技术中的瓶颈。在浅海近似均匀环境中,利用虚拟接收方法对声源测距的目标定位方法相比于传统的匹配场定位方法可以避免对环境参数和声场模型的依赖,同时省去生成拷贝场时的大量计算。通过数值模拟和实验数据处理,比较了在虚拟接收方法声源测距中不同信噪比的引导声源对目标声源测距的结果。提高引导声源的信噪比,可以一定程度上提高于涉条纹清晰度,从而提高测距准确度。提高引导声源的信噪比可作为目标声源的信噪比补偿是利用虚拟接收方法的目标定位技术的又一个优点。      

浅海中水平阵时反聚焦性能研究

在浅海波导中,垂直时反阵可以跨越整个波导,能对大多数简正波模态进行精确采样。相比垂直阵,水平阵因便于安装在舰艇或永久布在海底放而更具有实际意义。本文在给定声源及海洋环境信息的条件下,通过仿真计算在声源处取得了较好的聚焦效果。对比垂直阵,计算了同种环境下水平阵取得较好时反聚焦效果所需孔径的大小,并分析了水平时反阵孔径一定,基元数减小;发射信号频宽的变化对时反聚焦性能造成的影响。得出大孔径的水平时反阵具有较好的时反聚焦性能,窄带信号较单频信号能改善水平阵时反聚焦性能的结论。最后处理了2002年海试数据,根据反演出的海底参数选择其中两组信号数据做时反处理,水平距离的定位误差为1.9%和2.2%。     

非完整阵列接收下的虚拟接收目标定位技术

在浅海近似绝热环境中,利用虚拟接收方法对声源测距的目标定位方法相比于传统的匹配场定位方法可以避免对环境参数和声场模型的依赖,同时省去生成拷贝场时的大量计算·利用虚拟接收方法对声源测距主要是通过估计虚拟声场干涉条纹的斜率进行定位,而非完整阵列接收相当于引入了干扰项,破坏了虚拟声场干涉结构。引入了一种基于图像Hessian矩阵特征值分析的多尺度线性滤波器,通过数值模拟和实验数据处理,结果表明,该滤波器可以有效地增强干涉结构、检测和提取干涉图案中的条纹信息,提高非完整阵列接收条件下的虚拟接收目标定位技术的测距性能。      

高斯射线束方法在深海匹配场定位中的应用

匹配场定位作为一种水声被动定位方法,其拷贝场计算方法的精度和速度对定位效果和定位效率有着直接的影响。尤其在深海,目前浅海中常用的拷贝场计算方法如简正波法、抛物方程近似等在深海中往往存在计算效率不够、内存需求大、难以满足实际应用的需求。高斯射线束方法具有计算速度快,物理意义清晰,易于并行化处理等优点,非常适合于深海近程声场计算。通过数值仿真算例和海上实验数据的处理验证了高斯射线束方法用于拷贝场计算的有效性。仿真和实验数据处理结果表明,采用高斯射线束方法计算拷贝场在深海匹配场定位中有很好的定位效果.      

高斯射线束法在深海声源定位中的应用

在深海匹配场(Matched Field Processing-MFP)声源定位中,拷贝场模型的计算精度和速度对声源的定位效果和定位效率有着直接的影响。针对这一问题,本文数值仿真研究了深海匹配场定位中采用高斯射线束理论作为拷贝场计算模型的可行性。高斯射线束理论具有计算速度快,物理意义清晰,并且适合并行化处理等优点。文中利用不同水文环境、不同频域范围的大量仿真实验来证明该模型的适用性。结果表明,高斯射线束模型在深远海的声源定位中有很好的定位精度,并且在较低频段同样有效,可以作为深远海声源定位的拷贝场计算模型。     

Waveguide invariant analysis for modeling time-frequency striations in a range-dependent environment

The waveguide invariant is a useful parameter for understanding the behavior of interference patterns (e.g., striations in time-frequency plots) resulting from broadband acoustic sources in shallow water waveguides. It is possible to model these striations for range-dependent environments using conventional parabolic equation methods; although this approach can be computationally intensive as a full field must be created for each frequency and azimuthally dependent geometry. This letter discusses the formulation and use of a range-dependent waveguide invariant distribution that can be used to describe spectral striation patterns using a fraction of the computing power required by parabolic equation methods.     

Range-dependent seabed characterization by inversion of acoustic data from a towed receiver array

The MAPEX2000 experiments were conducted in the Mediterranean Sea in March, 2000 to determine seabed properties using a towed acoustic source and receiver array. Towed systems are advantageous because they are easy to deploy from a ship and the moving platform offers the possibility for estimating spatially variable (range-dependent) seabed properties. In this paper, seabed parameters are determined using a matched-field geoacoustic inversion approach with measured, towed array data. Previous research has successfully applied matched-field geoacoustic inversion techniques to measured acoustic data. However, in nearly all cases the inverted data were collected on moored, vertical receiver arrays. Results here show that seabed parameters can also be extracted by inverting acoustic measurements from a towed array of receivers, and these agree with those inverted using data received simultaneously on a vertical array. These findings imply that a practical technique could be developed to map range-dependent seabed parameters over large areas using a towed acoustic system. An example of such a range-dependent inversion is given using measurements from the MAPEX2000 experiments.     

Propagation in an elastic wedge using the virtual source technique

The virtual source technique, which is based on the boundary integral method, provides the means to impose boundary conditions on arbitrarily shaped boundaries by replacing them by a collection of sources whose amplitudes are determined from the boundary conditions. In this paper the virtual source technique is used to model propagation of waves in a range-dependent ocean overlying an elastic bottom with arbitrarily shaped ocean-bottom interface. The method is applied to propagation in an elastic Pekeris waveguide, an acoustic wedge, and an elastic wedge. In the case of propagation in an elastic Pekeris waveguide, the results agree very well with those obtained from the wavenumber integral technique, as they do with the solution of the parabolic equation (PE) technique in the case of propagation in an acoustic wedge. The results for propagation in an elastic wedge qualitatively agree with those obtained from an elastic PE solution.     

Compressive matched-field processing

Source localization by matched-field processing (MFP) generally involves solving a number of computationally intensive partial differential equations. This paper introduces a technique that mitigates this computational workload by "compressing" these computations. Drawing on key concepts from the recently developed field of compressed sensing, it shows how a low-dimensional proxy for the Green's function can be constructed by backpropagating a small set of random receiver vectors. Then the source can be located by performing a number of "short" correlations between this proxy and the projection of the recorded acoustic data in the compressed space. Numerical experiments in a Pekeris ocean waveguide are presented that demonstrate that this compressed version of MFP is as effective as traditional MFP even when the compression is significant. The results are particularly promising in the broadband regime where using as few as two random backpropagations per frequency performs almost as well as the traditional broadband MFP but with the added benefit of generic applicability. That is, the computationally intensive backpropagations may be computed offline independently from the received signals, and may be reused to locate any source within the search grid area.     

The array invariant

A method is derived for instantaneous source-range estimation in a horizontally stratified ocean waveguide from passive beam-time intensity data obtained after conventional plane-wave beamforming of acoustic array measurements. The method has advantages over existing source localization methods, such as matched field processing or the waveguide invariant. First, no knowledge of the environment is required except that the received field should not be dominated by purely waterborne propagation. Second, range can be estimated in real time with little computational effort beyond plane-wave beamforming. Third, array gain is fully exploited. The method is applied to data from the Main Acoustic Clutter Experiment of 2003 for source ranges between 1 to 8 km, where it is shown that simple, accurate, and computationally efficient source range estimates can be made.     

Matched-field depth estimation for active sonar

This work concerns the problem of estimating the depth of a submerged scatterer in a shallow-water ocean by using an active sonar and a horizontal receiver array. As in passive matched-field processing (MFP) techniques, numerical modeling of multipath propagation is used to facilitate localization. However, unlike passive MFP methods where estimation of source range is critically dependent on relative modal phase modeling, in active sonar source range is approximately known from travel-time measurements. Thus the proposed matched-field depth estimation (MFDE) method does not require knowledge of the complex relative multipath amplitudes which also depend on the unknown scatterer characteristics. Depth localization is achieved by modeling depth-dependent relative delays and elevation angle spreads between multipaths. A maximum likelihood depth estimate is derived under the assumption that returns from a sequence of pings are uncorrelated and the scatterer is at constant depth. The Cramér-Rao lower bound on depth estimation mean-square-error is computed and compared with Monte Carlo simulation results for a typical range-dependent, shallow-water Mediterranean environment. Depth estimation performance to within 10% of the water column depth is predicted at signal-to-noise ratios of greater than 10 dB. Real data results are reported for depth estimation of an echo repeater to within 10-m accuracy in this same shallow water environment.     

Source-Space Compressive Matched Field Processing for Source Localization

Source localization by matched-field processing(MFP) can be accelerated by building a database of Green's functions which however requires a bulk-storage memory.According to the sparsity of the source locations in the search grids of MFP,compressed sensing inspires an approach to reduce the database by introducing a sensing matrix to compress the database.Compressed sensing is further used to estimate the source locations with higher resolution by solving the l_1-norm optimization problem of the compressed Green's function and the data received by a vertical/horizontal line array.The method is validated by simulation and is verified with the experimental data.     

An experimental study on matched field processing in shallow water

I.IntroductionPassiverangeanddepthlocalizationofanacousticsourceinshallowwaterisadifficult,yetinterestingproblemthathasreceivedagreatdealofattentioninthelastfewyears['5].Thesimu1taneousestimationofrangeanddepthrequirestheuseofnumericalpropagationmodels.Theclassicalapproachtothisproblemisto"match"thereceivedacousticdatawiththesoundfieldpredictedbythepropagationmodelforanumberofhypotheticalrange/depthsourcelocatiolls.Thistechniqueiscalledmatchedfieldprocessing.Itiscommonlyacceptedthatthewavepro…