二维解卷积波束形成水下高分辨三维声成像

针对水下三维成像的空间分辨率难以提高,且具有较高旁瓣级的问题,提出了一种二维解卷积波束形成高分辨三维声成像算法,该算法首先完成任意距离切片的平面阵波束形成,近场情况下采用菲涅尔近似实现近场平面阵波束形成,然后通过二维解卷积技术对任意距离切片的二维波束形成结果进行解卷积处理,去除阵列指向性函数的影响,改善波束响应非理想冲击函数所造成波束形成主瓣宽及旁瓣级高的问题。通过计算机仿真分析,新算法可以有效的提高水下三维成像的空间分辨率,抑制旁瓣级,并能够在较宽频带和不同阵列孔径内保持与常规波束形成相当的稳定性。通过试验研究,新方法比常规波束形成实际目标成像分辨率提高一倍,最高旁瓣级下降20 dB,验证了该算法在实际系统中的有效性.      

球谐域混叠消除最优波束形成方法EI北大核心CSCD

为解决现有的球谐域混叠消除波束形成方法设计目标单一、难以很好地兼容多变的应用场景的问题,提出了球谐域混叠消除最优波束形成方法,并建立了其二阶锥规划形式的多重约束凸优化数学模型。得益于该数学模型,提出了旁瓣约束的混叠消除最大指向性波束形成器、鲁棒的混叠消除最大指向性波束形成器、混叠消除最小方差无失真响应波束形成器、零点约束的混叠消除最大指向性波束形成器。提出方法继承了现有球谐域混叠消除波束形成方法的混叠消除功能,且能够在指向性指数、白噪声增益、旁瓣水平等多个冲突的性能指标之间寻求适宜折中,便于用户根据实际应用需求灵活地调整约束参数得到特定场景下综合性能最优的波束形成器。     

基于分组时延预处理的时域波束形成方法*

对于不等强度多目标情况下的弱目标检测问题,依据波束形成归一化指向性函数在目标方向上输出值为1、在非目标方向上输出值为小于1的特性,提出一种基于分组时延预处理的时域波束形成方法。该方法首先对线列阵接收数据进行分组处理;然后,按搜索角度对各组数据进行时延预处理,并对各组预处理结果进行相加,得到一组新数据;最后,对该组新数据按时域波束形成进行处理,得到该搜索角度对应波束值。理论推导、数值仿真和试验数据处理结果均表明：相比常规时域波束形成,该方法所得波束形成指向性函数发生了变化,旁瓣级得到了13dB以上的改善,降低了强目标旁瓣级对弱目标检测的影响。     

任意几何形状和阵元指向性的传感器阵列优化波束形成方法

针对常规波束运用到实际传感器阵列时旁瓣较高这一缺点,提出了适用于任意几何形状和阵元指向性的传感器阵列的两种旁瓣约束优化波束形成方法。一种是主瓣宽度约束条件下的最低旁瓣波束形成,另一种是在所能允许的最高旁瓣约束条件下的高增益波束形成。通过对加权向量范数进行约束,提高波束形成的稳健性。这两种优化波束形成问题都可以写成二阶锥(Second-OrderCone)约束优化的形式,然后利用已有的内点方法(Interior-PointMethods)求出其数值解。计算机仿真和湖上实验数据处理结果表明,该低旁瓣波束形成方法相比于常规波束和其它基于自适应波束形成的旁瓣控制方法,在同等主瓣宽度的情况下可以获得更低的旁瓣级;该高增益波束形成方法在同等旁瓣级约束条件下可以获得更高的阵增益,而且旁瓣级能够满足设定要求。     

用于自适应波束形成语音增强的球谐域掩蔽函数估计方法

提出一种用于球形阵列自适应波束形成的掩蔽函数估计方法。该方法利用包含空间信息的球谐系数提取低维空间向量,并采用复高斯混合模型和深度学习两种方案来估计掩蔽函数,最终利用估计的掩蔽函数设计最小方差无失真响应波束形成器,以达到空域滤波的效果。理论分析和仿真实验证明,对于相同时长的声信号,球谐域掩蔽函数估计方法的计算复杂度比传统阵元域估计方法低了一个数量级。并且在大部分声场环境中,尤其在低信噪比情况下,所提方法的语音质量感知评估测度得分、分段信噪比和短时客观可懂度明显高于阵元域方法,三者最高分别可提升1.31 dB,4.54 dB和35%。另外,实际声学环境的测量实验也验证了所提方法在不影响可懂度的条件下比传统阵元域方法具备更高的降噪量。      

线性约束自适应逆波束形成研究

逆波束形成较常规波束形成有较好的方位分辨力,但其旁瓣较高,为抑制旁瓣并进一步提高阵增益和方位分辨力,本文提出一种自适应逆波束形成方法,通过设计自适应滤波器对虚拟阵列进行加权,提高阵增益和方位分辨力。理论分析表明自适应逆波束形成能够抑制旁瓣和噪声,阵增益较常规波束形成和逆波束形成提高约3 d B,数值仿真结果表明,自适应逆波束形成的旁瓣降低,阵增益和方位分辨力提高,实验数据处理结果表明自适应逆波束形成具有良好的方位分辨能力和目标检测能力,从而验证了其抑制旁瓣、提高方位分辨力和阵增益的有效性。     

基于超指向性多极子矢量阵的水下低频声源方位估计方法研究

针对水下低频声源的方位估计问题,基于基元紧密排列的二维矢量阵,建立了一种超指向性波束形成方法.根据矢量基元差分运算构建各阶多极子模型,获得了几乎与频率无关的模态函数,并经加权计算可在低频条件下实现超指向性波束,以解决阵列孔径对波束性能的限制.同时,结合输出信噪比最大准则所得波束,分析了超指向性波束形成算法的稳定性与波导的影响程度,探索模态阶数与阵列参数的选取原则.通过阵列性能的仿真计算与实际阵列的测量数据表明,该算法可在小尺寸阵列孔径下获得良好的阵列波束,兼具了水下线型超指向性阵和环形超指向性阵的优点,可有效实现水下低频声源的水平方位估计;且波束性能可通过调节模态阶数与基元间距以达到最佳,并受水下声波导多途与频散效应影响有限.     

一种加权稀疏约束稳健Capon波束形成方法

为了克服标准Capon波束形成器旁瓣级高以及存在角度失配时性能急剧下降等缺点, 在稀疏约束Capon波束形成器的基础上, 提出了一种加权稀疏约束Capon波束形成器. 该方法利用波束响应的稀疏分布特性, 在标准Capon波束形成优化模型中加入旁瓣区域波束响应稀疏约束(l₁ 范数约束), 使旁瓣区域波束响应向量中非零元素的个数最小化; 通过阵列采样数据协方差矩阵特征分解得到信号子空间及噪声子空间, 利用信号子空间与噪声子空间的正交特性, 构造加权矩阵对稀疏约束进行加权, 使得稀疏重构时波束响应向量中不同角度对应的元素得到不同程度的约束. 该方法有效地抑制了Capon波束形成器的高旁瓣级, 加深了干扰方位零陷, 提高了阵列输出信干噪比. 由于稀疏约束, 波束响应向主瓣集中, 期望信号方向附近的波束响应都较大, 从而也提高了阵列抗导向矢量角度失配的能力. 数值仿真和水池实验验证了所提方法的有效性.     

基于空时级联滤波的拖船自噪声抵消方法

拖船自噪声属于近场多途强干扰信号,具有显著角度扩展现象,是影响拖曳阵探测性能的重要因素之一。在逆波束形成自噪声抵消方法基础上,结合空域和时域滤波,提出了空时级联滤波的拖船自噪声抵消方法。首先,由方位估计器估计拖船自噪声方位,经过波束形成空域滤波估计得到自噪声信号;然后,利用自噪声空域滤波输出设计最优维纳滤波器,将自噪声抵消在阵元级。基于简正波声场模型的仿真和实际海试数据的处理表明,该方法能够有效抵消拖船自噪声,性能优于逆波束形成方法。     

基于凸优化的时域宽带旁瓣控制自适应波束形成

提出了基于凸优化的时域宽带旁瓣控制自适应波束形成方法。首先将基阵波束响应表达成一组FIR滤波器系数的线性函数,然后采用如下的优化准则来设计FIR滤波器组:在保证波束形成器对期望方向信号无失真输出且波束旁瓣低于设定值的条件下,使波束输出功率最小化。同时通过对滤波器系数的范数进行约束来保证波束形成器的稳健性。该波束形成器设计问题被表述成二阶锥规划的凸优化问题来求解。仿真结果验证了所提出方法的有效性。     

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.     

Imaging of directional distributed noise sources

This study relates to the acoustic imaging of noise sources that are distributed and strongly directional, such as in turbulent jets. The goal is to generate high-resolution noise source maps with self-consistency, i.e., their integration over the extent of the noise source region gives the far-field pressure auto-spectrum for a particular emission direction. Self-consistency is possible by including a directivity factor in the formulation of the source cross-spectral density. The resulting source distribution is based on the complex coherence, rather than the cross-spectrum, of the measured acoustic field. For jet noise, whose spectral nature changes with emission angle, it is necessary to conduct the measurements with a narrow-aperture array. Three coherence-based imaging methods were applied to a Mach 0.9 turbulent jet: delay-and-sum beamforming; deconvolution of the beamformer output; and direct spectral estimation that relies on minimizing the difference between the measured and modeled coherences of the acoustic field. The delay-and-sum beamforming generates noise source maps with strong spatial distortions and sidelobes. Deconvolution leads to a five-fold improvement in spatial resolution and significantly reduces the intensity of the sidelobes. The direct spectral estimation produces maps very similar to those obtained by deconvolution. The coherence-based noise source maps, obtained by deconvolution or direct spectral estimation, are similar at small and large observation angles relative to the jet axis.     

水下声成像中旁瓣抑制方法及其实验研究

提出了一种近场条件下采用不等间隔阵并进行孔径变迹处理的水下声成像旁瓣抑制方法,并进行了理论和实验研究。考虑以球面波传播理论为基础的聚焦波束形成,首先通过阵元位置微调,设计了可实现低旁瓣的不等间隔阵,从单程波束响应上降低旁瓣;然后,将孔径变迹处理方法应用于水下声成像中,全部阵元用于接收,部分阵元用于发射,从双程波束响应上进一步降低旁瓣。通过水池实验对所提出的方法进行了验证。结果表明:采用不等间隔阵并进行孔径变迹处理可以更为有效地降低旁瓣,而主瓣仅有小量展宽,且该方法工程应用简便易行,在改善成像质量的同时降低了系统复杂度。      

利用线谱起伏实现目标测距

常见水中目标辐射噪声的线谱会随目标运动而出现强弱起伏。不同号简正波之间的干涉是目标声强随距离起伏的主要原因,利用简正波水平波数差和波导不变量之间的关系,推导了不同线谱随距离变化起伏的理论关系式。基于此关系式,提出利用两条或多条线谱声强起伏进行声源测距的方法。针对两条线谱起伏测距方法存在的旁瓣问题,解释其形成原因,并提出用多条线谱声强起伏抑制旁瓣。数值仿真验证了方法的可行性,利用多条线谱声强起伏测距的方法可有效抑制旁瓣。海试数据分析表明,当连续谱部分非常微弱无法有效测距时,利用多条线谱声强起伏测距的方法仍能稳定的估计渔船目标距离,估计距离的平均相对误差为12%。      

Wideband RELAX and wideband CLEAN for aeroacoustic imaging

Microphone arrays can be used for acoustic source localization and characterization in wind tunnel testing. In this paper, the wideband RELAX (WB-RELAX) and the wideband CLEAN (WB-CLEAN) algorithms are presented for aeroacoustic imaging using an acoustic array. WB-RELAX is a parametric approach that can be used efficiently for point source imaging without the sidelobe problems suffered by the delay-and-sum beamforming approaches. WB-CLEAN does not have sidelobe problems either, but it behaves more like a nonparametric approach and can be used for both point source and distributed source imaging. Moreover, neither of the algorithms suffers from the severe performance degradations encountered by the adaptive beamforming methods when the number of snapshots is small and/or the sources are highly correlated or coherent with each other. A two-step optimization procedure is used to implement the WB-RELAX and WB-CLEAN algorithms efficiently. The performance of WB-RELAX and WB-CLEAN is demonstrated by applying them to measured data obtained at the NASA Langley Quiet Flow Facility using a small aperture directional array (SADA). Somewhat surprisingly, using these approaches, not only were the parameters of the dominant source accurately determined, but a highly correlated multipath of the dominant source was also discovered.     

近场反卷积聚焦波束形成声图测量

为了提高声图测量中对多个声源的分辨能力和定位精度,给出了一种近场二维反卷积聚焦波束形成声图测量方法。推导了水下声图测量的广义卷积模型,根据声图测量中点传播函数移变但可预测的特点,通过预存点传播函数字典的方式,将波束形成过程中的卷积问题转化成叠加积分问题,并应用二维Richardson-Lucy迭代算法实现了二维移变模型情况下的近场二维反卷积求解,从而实现高分辨声图测量。通过仿真和海试对比了反卷积、常规声图测量和MVDR声图测量的性能,结果表明反卷积算法在500次迭代情况下聚焦峰尺度小于另外两种算法的1/2,旁瓣级下降超过6 dB.      

Active control of passive acoustic fields: passive synthetic aperture/Doppler beamforming with data from an autonomous vehicle

The maneuverability of autonomous underwater vehicles (AUVs) equipped with hull-mounted arrays provides the opportunity to actively modify received acoustic fields to optimize extraction of information. This paper uses ocean acoustic data collected by an AUV-mounted two-dimensional hydrophone array, with overall dimension one-tenth wavelength at 200-500 Hz, to demonstrate aspects of this control through vehicle motion. Source localization is performed using Doppler shifts measured at a set of receiver velocities by both single elements and a physical array. Results show that a source in the presence of a 10-dB higher-level interferer having exactly the same frequency content (as measured by a stationary receiver) is properly localized and that white-noise-constrained adaptive beamforming applied to the physical aperture data in combination with Doppler beamforming provides greater spatial resolution than physical-aperture-alone beamforming and significantly lower sidelobes than single element Doppler beamforming. A new broadband beamformer that adjusts for variations in vehicle velocity on a sample by sample basis is demonstrated with data collected during a high-acceleration maneuver. The importance of including the cost of energy expenditure in determining optimal vehicle motion is demonstrated through simulation, further illustrating how the vehicle characteristics are an integral part of the signal/array processing structure.     

Obtaining absolute acoustic spectra in an aerodynamic wind tunnel

Cost effective methods for identifying and reducing sources of noise have become essential in the design of many modern transport vehicles. Whilst closed-section wind tunnels can readily evaluate aerodynamic performance, obtaining accurate acoustic spectra is often a major challenge because of the poor signal to noise ratios available. In this paper, methods of obtaining absolute spectra from the non-acoustically treated Markham wind tunnel at the University of Cambridge are discussed. Initial measurements with a small monopole source compare well with simulations and show that it is possible to obtain similar spectra from two nested acoustic arrays. However, a series of further experiments with simplified landing gear models show very different spectra from each array. By comparing measurements with simulations, it is shown that negative side lobes affect beamforming source maps. Measurements of an ‘empty tunnel’ cross spectral matrix allow the removal of sidelobes, providing much greater consistency between spectra. Finally, a dipole beamforming vector is used to account for the directivity of the landing gear noise, leading to good agreement between absolute spectra from the differently sized arrays. This analysis demonstrates that data from a phased array in a hard-walled, aerodynamic wind tunnel can provide meaningful acoustic spectra from low-noise models.     

基于波束形成缩放声强的声源局部声功率计算

基于波束形成法识别噪声源时,为计算主要噪声源的辐射声功率,给出了基于平面波模型的声强缩放方法,模拟计算了单极子点声源局部声功率的计算误差,结果显示:当阵列平面与声源计算平面间距离等于阵列直径时,基于波束形成缩放声强计算的声功率误差仅略高于0.1 dB。为克服旁瓣干扰,给出了具有一定动态范围的声源计算平面积分法,模拟计算了单极子点声源的局部声功率,结果表明:该积分法的计算值与主瓣区域积分法的计算值近似相等,均约等于理论声功率。进一步,波束形成法与声强法的对比算例试验验证了基于波束形成缩放声强计算声源局部声功率方法的有效性。