浅海时变声速环境下的自适应匹配场定位算法实现*

针对浅海环境下声速剖面失配引起的匹配场处理器失配问题,提出了一种自适应匹配场定位算法在声速剖面时变环境下的实现方式。将先验声速剖面集简化为经验正交函数表示,结合蒙特卡洛方法与环境扰动约束算法对当下时刻的目标声源进行匹配场定位。本文以某次试验获取的连续20小时的声速剖面数据为研究对象,通过仿真试验对该算法进行验证,结果表明：在先验声速剖面集的半小时之后,利用自适应算法的距离和深度定位成功率较常规匹配场算法有较大提升,其中,深度正确定位概率相对较低。     

Matched localization of a horizontal array in shallow sea

I.IntroductionInsha1lowsea,passivesource1ocalizationisadifficu1t,yctinterestingprob1emthathasre-ceivcdagrcatdca1ofattcnti0ninthelastfCwycars.l'-'1Theconventiona1sourccloca1izationistOmatchthercceivcdacousticdatawiththesoundficldprcdictcdbythepropagationmodcl.Thistechniqueiscallcdmatchcd-ficldproccssing(MFP).Itiscommonlyacceptcdthatinshal-low-watercnvironmcnLssoundficldcanbcwclldcscribcdbyanormal-modemodel.Accord-ingtothismodcl,thcacousticprcssurecanbecxprcsscdasalincarcombinationofthenorma…     

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。     

浅海中水平线列阵深度对匹配场定位性能的影响

以浅海声传播模型为基础,通过计算机仿真观察到以下物理现象：浅海中海底水平线列阵的匹配场定位性能优于其他深度水平线列阵.利用简正波建模方法揭示了这一现象的物理机理.按照简正波理论,各号模式的形状是海水深度的函数.通过比较不同深度上各号模式幅度的变化,发现海底模式幅值接近零的模式号数明显小于其他深度.这说明海底水平线列阵可以对更多号模式进行采样,进而获得更多的目标声源信息,取得更好的匹配场定位效果. 关键词： 水平线列阵 匹配场定位 基阵深度     

Waveguide invariant focusing for broadband beamforming in an oceanic waveguide

The performance of broadband sonar array processing can degrade significantly in shallow-water environments when interference becomes angularly spread due to multipath propagation. Particularly for towed line arrays near endfire, elevation angle spreading of multipath interference often results in masking of weaker sources of interest. While adaptive beamforming in a series of narrow frequency bands can suppress coherent multipath interference, this approach requires long observation times to estimate the required narrowband covariance matrices. To form wideband covariance matrices which can be estimated with less observation time, plane-wave focusing methods have been used to avoid interference covariance matrix rank inflation. This paper extends wideband focusing to the case of coherent multipath interference. The approach presented here, called waveguide invariant focusing (WIF), exploits a robust relationship for the frequency dependence of horizontal wave number differences. Unlike matched-field methods, WIF does not model multipath wave fronts but rather makes the interference appear to occupy the same rank-one subspace across frequency. This permits formation of wideband covariance matrices without interference rank inflation. Simulation experiments in a realistic ocean environment indicate that adaptive beamforming using WIF covariance matrices can provide a significant array gain improvement over conventional adaptive methods with limited observation time.     

深海声影区时频谱干涉结构与声源定位

被动声呐探测位于深海声影区的水面舰船辐射噪声时,接收信噪比通常较低,导致声源被动定位方法的性能较差。针对这一问题,提出一种利用接收信号时频谱干涉结构的声源距离和径向速度联合估计方法。首先根据射线声学理论,建立时频谱沿频率轴和时间轴的干涉条纹周期与声源距离和径向速度的关系,然后对接收信号时频谱进行二维傅里叶变换和多频带处理以估计上述干涉条纹周期,最后解算声源距离和径向速度。仿真和海试数据处理结果表明,相比于现有利用接收信号自相关的声源距离估计方法,该文利用时频谱二维傅里叶变换的声源定位方法具有较好的稳健性,比较适用于低信噪比条件下的声源被动定位。     

Localization using Bartlett matched-field processor sidelobes

Ambiguity surface sidelobes generated by the Bartlett matched-field processor (MFP) shift location with frequency. This sidelobe shift can be viewed as a continuous trajectory in a range-frequency plane at a fixed depth, where the trajectories converge to the correct source range for a perfectly matched surface. In isovelocity or bottom-interacting environments the sidelobe trajectories are straight lines that converge to the true range at zero frequency, while environments with upward-refracting sound-speed profiles have trajectories that asymptotically converge as the frequency approaches infinity. This behavior can be explained by the theory of waveguide invariants, which predict the local behavior of interference maxima/minima of acoustic intensity in the frequency-range plane. As the ambiguity surface of the Bartlett matched-field processor has a physical interpretation in terms of a time-reversed acoustic field, with the sidelobes analogous to local interference maxima, these invariant concepts can be reformulated for application to MFP. These interference trajectories are demonstrated to exist in simulations, broadband source tows, and a type A blue whale vocalization. Sidelobe trajectories also exist in the range-depth plane, but they contain no information about the correct source depth. An appendix demonstrates how these sidelobe properties can be exploited when combining ambiguity surfaces through use of gradient and Radon transform information. The resulting range estimators demonstrate better peak-to-sidelobe ratios than a simple incoherent average.     

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.      

Array Acoustic Signal Processing in Shallow-Water Channels under Conditions of a Priori Uncertainty: Estimates of the Efficiency Loss

The objective of this study is a comparative analysis of the efficiency of the matched-field and optimal spatial signal processing methods in a shallow-water sound channel under conditions of inaccurate knowledge of its parameters. It is assumed that a signal of a remote localized source is received by a vertical antenna array against the background of an intense interference, which is also created by a localized source, while the vertical profile of the sound velocity, the channel depth, the sound velocity in underlying bottom, and its density are known with arbitrary deviations from actual values within specified intervals. The processing efficiency is characterized by the array gain in terms of the signal/(noise + interference) ratio normalized to the number of the array elements. The stochastic modeling technique is used to show that with an increase in the a priori uncertainty in the estimation of these parameters, the efficiency losses for these two processing methods not only have significantly different values, but can reveal the nonmonotonic character. The permissible error levels in the estimation of the channel parameters are determined, at which the gain loss does not exceed the specified level (3 dB) for each of the methods. The results are important to specify the requirements for facilities of operational oceanography that provide the effective operation of receiving antenna systems in real shallow-water conditions.

     

基于频散特征的单水听器模式特征提取及距离深度估计研究

针对浅海环境中低频宽带水声脉冲信号, 研究基于频散特征结合时频分析的单水听器距离和深度估计方法. 以简正波理论为依据, 将单水听器上的接收信号表示成一系列传播模式之和的形式, 分析了经典波导环境下的频散现象, 采用自适应径向高斯核函数的时频分析方法来表征接收信号的频散特征. 为提高时频分辨率, 采用自适应径向高斯核函数的时频分布来提取频散关系曲线中传播模式的到达时间差, 利用模式的到达时间差估计声源的距离. 采用多模式联合匹配的方式, 通过二值掩模滤波的时频滤波方法, 提取所需的模式. 通过计算实际提取出的模式能量与预测的模式能量之间的误差, 建立代价函数, 并通过模式能量匹配的方式, 确定声源的深度. 通过对基于Pekeris波导模型的浅海环境进行仿真验证, 结果表明: 自适应径向高斯核函数的时频分析方法能够很好地反映信号本身的频散特征, 具有较高的时频分辨率, 克服了传统短时傅里叶变换时频表征的限制, 使得模式在时频域更加容易辨识和分离; 从测距效果来看, 不同模式组合下的距离估计结果不同, 采用在时频面上具有较高能量的模式, 可得到较为准确的距离估计; 选用高能量的模式所得的距离估计的相对误差小于2%. 在定深方面, 参与联合匹配的模式个数越多, 代价函数的峰值更加地尖锐, 同时具有低的伪峰, 深度估计的性能会进一步有所提升. 该工作对于研究低频水声脉冲信号的分离和提取具有重大意义. 关键词： 频散信道 时频分析 单水听器 定位     

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.     

利用海底反射信号进行地声参数反演的方法

针对现有反演方法的缺点,提出了一种基于海底反射信号的地声参数高分辨反演方法.它利用短距离声源在不同深度上发射宽带线性调频信号,采用垂直阵进行接收,首先通过匹配滤波方法提取多径到达信息,然后利用海底反射损失曲线,反演海底表层的声速和密度,最后利用浅底层反射信号估计沉积层参数.由于海水中直达波受到内波的强烈影响,选择海底表面反射作为参考,用以可靠地计算浅底层反射的相对到达时间和幅度,从而估计出沉积层的厚度、速度和衰减系数.通过海上实验,验证了利用浅底层反射信号反演参数的有效性. 关键词： 海底参数 反演 浅底层反射信号     

Experimental testing of the noise-canceling processor

Signal-processing techniques for localizing an acoustic source buried in noise are tested in a tank experiment. Noise is generated using a discrete source, a bubble generator, and a sprinkler. The experiment has essential elements of a realistic scenario in matched-field processing, including complex source and noise time series in a waveguide with water, sediment, and multipath propagation. The noise-canceling processor is found to outperform the Bartlett processor and provide the correct source range for signal-to-noise ratios below -10 dB. The multivalued Bartlett processor is found to outperform the Bartlett processor but not the noise-canceling processor.     

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.     

Frequency invariability of acoustic field and passive source range estimation in shallow water

The frequency invariability of the warped modal signal and the warped signal autocorrelation function in shallow water is discussed.A method is proposed for passive source-range estimation based on the frequency invariability and warping transform of signal autocorrelation function received by a single hydrophone in a range-independent or weak range-dependent shallow water environment.In the method,a guided source with a known range is employed to provide the crucial and relative invariant scaled features.The experimental data in shallow water with an iso-speed profile and a fluctuated thermocline are used to verify this approach.The relative errors of the source range estimation are basically less than 10%.     

风成噪声背景下垂直阵阵列信噪比随声源深度的变化规律

风成噪声是海洋中最广泛存在的环境噪声、是被动声纳处理性能的重要影响因素.它具有一个典型的物理性质是很大程度上只对应中高阶模态.阵列信噪比计入了阵列采样辐射声强、背景噪声功率和阵处理增益,是决定声纳阵列处理性能的关键物理量.本文研究了受风成噪声模态结构影响,典型夏季浅海环境中垂直阵阵列信噪比随声源深度的变化关系.在简正波模深函数采样完整的假设条件下,理论证明了阵列信噪比随声源深度的变化可近似为低阶模态幅度强度(模深函数模值的平方)随深度变化的线性叠加,且模态阶数越低,贡献越大;并且,在强风成噪声背景、显著负梯度环境下该变化规律可由1阶模态幅度强度随深度的变化近似独立表征.以上结果表明,在同一声源距离条件下,声源置于水体下半部分时的阵列信噪比比置于海面附近更大,并且在位于1阶模态峰值点所在深度附近时达到最大.典型负声速梯度浅海环境中的仿真实验结果对理论分析进行了验证,并表明在一定条件下阵列信噪比随声源深度的变化与声源距离近似无关.     

单水听器波导不变量被动测距

本文主要讨论利用声场干涉现象由单水听器被动测距的可行性及测距性能,为此提出了单水听器波导不变量被动测距方法,通过提取LOFAR图上干涉条纹、使用简正波模型计算波导不变量、频域相关法估计相对速度,最后依据干涉条纹方程得到声源距离估计量。数值仿真和海上实验结果验证了单水听器被动测距的可行性,并具备一定测距性能,在3 dB信噪比环境中,对于7 km处的运动声源,平均测距误差小于5%。本文方法具有设备简单、易于推广至阵列信号处理等特点,为声纳信号处理环境宽容性的提高及环境适配声纳的设计开拓了思路。     

The effects of the internal waves on temporal correlation of matched-field processing in shallow water

Effects of linear and solitary internal waves on the temporal correlation of matched-field processing(MFP) in shallow water are numerically investigated for acoustic sources with different frequencies and depths based on oceanographic data from an experiment.It is shown that the temporal correlation of MFP decreases as the amplitude of solitary internal waves or the average energy density of linear internal waves increases.For acoustic source with lower frequency or located below the thermocline,the temp...     

深海会聚区声场多途时延差分析及声源距离估计*

深海会聚区声道由于具有传播距离远、传播损失低等优势,对实现声呐远程探测具有十分重要的意义。本文基于虚源理论推导了深海会聚区的多途到达时延结构,给出了会聚区内不同声线路径的时延差曲线随接收深度变化的近似表达式,通过分析时延差曲线与声源水平距离之间的关系,提出了一种利用多途时延差估计深海会聚区近海面声源距离的方法,仿真实验验证了该方法原理的正确性。南海实验结果表明,当收发距离在42km~52 km时,会聚区爆炸声源距离估计结果同实际爆炸距离吻合较好,估计误差为0.6%~6.1％,验证了该方法的有效性。     

一种水平变化波导中匹配场定位的虚拟时反实现方法

在水平变化波导中,匹配场被动定位的计算量非常大,严重阻碍了其工程应用.本文提出了一种水平变化波导中匹配场定位的虚拟时反实现方法,其抛物方程模型计算网格总数远小于匹配场处理,从而大大减小计算代价.与匹配场处理不同,虚拟时反实现方法是一个利用介质互易性和叠加性的后向传输过程.通过在各水听器位置放置虚拟声源,并在搜索区域产生相应的模糊平面,对各个模糊平面进行相应加权求和,获得的定位模糊平面.利用地中海浅海实验数据验证了虚拟时反实现方法的快速性能.