基于水听器阵的广义相关波束形成算法研究

传统上都是使用基于常规波束形成(CBF)输出功率的不同进行声源的被动检测和定位。广义相关波束形成,是一种旨在将平均Toep litz相关函数用于估计波束形成的输出功率。从线性矢量水听器阵出发,分析了常规波束形成,对广义相关波束形成(GCBF)进行了深入研究,通过对广义相关波束形成器进行“W ilson”和“Bartlett”加权,可以分别得到FIM(WFIM)和CBF,对这三种波束形成器进行了理论分析和计算机仿真,结果表明三个波束形成器的分辨能力从高到低依次是:FIM、WFIM、CBF。     

圆阵低频超增益波束形成用于水下目标探测研究

针对小尺度基阵难以取得低频空间增益的问题,研究了圆阵超增益波束形成技术检测低频目标的方法。利用小尺度基阵低频噪声的空间相关性,求出基阵的相关系数矩阵,该矩阵对常规波束形成的权系数进行加权,产生超增益波束形成器的最优加权向量。计算机仿真与实测数据处表明：超增益波束形成技术能够在较低的工作频率上形成波束,获得更好的探测定位性能,有良好的应用前景。     

基于高阶累积量的自适应波束形成

常规波束形成器仅限于利用信号的二阶统计特性。作者采用高阶累积量估计期望信号的导向矢量 (Steering Vector) ,实现了一种基于高阶累积量的自适应波束形成器 (HCAB)。该波束形成器利用信号的更高阶统计特性 ,减少了对阵列流型的依赖 ,具有较好的容差性 ,能自动跟踪信号。数值模拟实验表明该波束形成器工作良好。     

强干扰背景下水中微弱信号的垂直阵波束形成研究

针对垂直阵在强干扰背景下采用常规波束形成方法难以估计目标俯仰角的问题,研究了超波束与逆波束形成等方法在垂直阵中的应用。讨论了超波束与逆波束形成原理,仿真分析了其波束图,表明分辨率比常规波束形成有明显提高。实测数据分析表明：超波束方法可以分辨目标与干扰的俯仰角轨迹,对角加载逆波束 MVDR 方法可以获得目标的俯仰角轨迹。研究结果解决了强干扰背景下微弱目标信号俯仰角难以估计的问题,为微弱目标定位提供了新的途径。     

适用于U型阵多波束系统的高分辨底检测算法

在多波束回声声纳系统中,高分辨处理算法例如MUSIC、ESPRIT,被广泛应用于海底地形的测绘。在应用高分辨算法时,一条均匀线阵是必要条件。然而,由于系统覆盖范围/分辨率的需求以及安装空间的限制,在多波束系统中经常会采用特殊形状的接收阵列,这使得高分辨算法无法直接应用。同时回波信号的短时平稳特性使得难以估计出协方差矩阵,这也增加了高分辨算法在多波束系统中的应用难度。本文首先介绍一种基于多角度子阵波束形成的ESPRIT算法,该算法能降低高分辨算法对信噪比、样本点数和计算能力的要求。仿真表明此算法能提供更好的分辨力。接着提出一种将基于多角度子阵波束形成的ESPRIT算法与虚拟阵列变换相结合的高分辨底检测算法,并针对高分辨底检测算法在U型阵上的应用进行了探讨。计算机仿真和试验数据处理结果验证了文章所提高分辨底检测算法的有效性。     

基于Notch窄带波束形成的俯仰角估计仿真

波束形成最重要的目的是定向,线列阵的波束形成技术在水声领域中作为接收和检测信号的基本方法已被广泛运用。由于方位估计需要大孔径基阵,而在水中兵器中,为解决小平台目标俯仰角估计问题, 提出一种基于线列阵的 Notch 窄带波束形成方法。主要介绍了基于线列阵的 Notch 窄带波束形成的结构、概念和实现方法,以及基于实测数据条件下的目标俯仰角估计仿真。     

可扩展孔径阵方位估计误差仿真分析与实验研究

针对可扩展孔径阵方位估计误差在工程使用中受装载平台影响大的问题,开展建模仿真与实验研究.基于一种装载于移动无人平台的双层圆柱形孔径可扩展的多元线列阵开展建模,根据实际使用的场景和安装平台,设计了具备时延补偿功能的波束形成算法和自适应姿态补偿算法.通过仿真分析和实验验证,证明该方法可有效减小该种可扩展孔径阵的方位估计误差...     

舰载声纳波束稳定与俯仰的研究

当船体发生摇摆或者需要将波束指向不同深度的水层时,需要对舰载声纳的波束进行稳定或俯仰控制。文章推导了甲板坐标系和大地坐标系之间的变换关系,并基于圆柱阵声纳,分析讨论了在不同的波束俯仰角下,圆柱阵换能器二维波束形成的性能。当俯仰角度较小时,在垂直方向上进行粗分层即可达到较好的性能;当俯仰角度较大时,则必须要对各阵元进行更精细的延迟控制。     

时空联合估计权向量的MVDR自适应波束形成方法

为实现短数据条件下权向量的稳定优化估计,提出1种时空联合估计权向量的MVDR自适应波束形成方法。该方法结合时域解析信号的MVDR自适应波束形成算法中构造时域解析信号的方法和直接数据域算法中空间滑动的方法,以减少一半权向量为代价,实现了在更短的数据长度下稳定优化地估计协方差矩阵和权向量。数值仿真实验和海上实验数据处理结果表明:与常规波束形成和直接数据域相比,该方法具有更好的稳定性和更好的波束性能,即主瓣更窄,旁瓣更低,阵增益更高。     

高分辨率波束形成器在多波束测深系统中的应用

对于海底地形测量,基于FT波束形成的幅度检测法空间分辨率较低,只能较准确给出有限测点的水深信息;平坦海底前提下,分裂子阵检测法或多子阵检测法可以得到连续测点的水深信息,复杂海底地形条件下,这两种方法均难以应用。能否利用高分辨率波束形成器来提高测深系统的空间分辨率是一个值得研究的问题。使用ESPRIT波束形成器处理了多波束测深系统的试验数据,并就其性能与FT波束形成器进行了比较与分析。     

Accurate Acoustic Signal Parameter Estimation for Marine Geodesy Surveys

Acoustic signal parameter estimation is important for diverse marine geodesy surveys and several other applications. However, the received signal from a far-field target characterized by planar wavefront propagation is frequently affected by strong nearby interfering signals. Their presence deteriorates the performance of direction-of-arrival (DOA) estimation for far-field target. In order to enhance the reception of signal from far-field target, the near-field/far-field (NFFF) beamformer is proposed. Such a beamformer optimizes beam pattern for far-field detection by maximizing beamformer output in the direction of the far-field target with the imposed condition to eliminate interfering signals generated in near-field locations. As the interference suppression only occurs at the position of near-field interference, a possible blind zone for far-field detection in conventional methods is not created. The NFFF beamformer is applicable for coherent signals and the scenario with multi interferences. For stationary situation where interferers locations are fixed, the NFFF beamformer computations do not require time updates with associated computational load. Furthermore the proposed method can be extended to several new situations such as acoustic monitoring performed from a stationary platform subjected to water currents, waves, winds and other variables, all of them generating nearby interferences and also to different array configurations including 2D and 3D arrays.     

Adaptive port-starboard beamforming of triplet sonar arrays

For a low-frequency active sonar (LFAS) with a triplet receiver array, it is not clear in advance which signal processing techniques optimize its performance. Here, several advanced beamformers are analyzed theoretically, and the results are compared to experimental data obtained in sea trials. Triplet arrays are single line arrays with three hydrophones on a circular section of the array. The triplet structure provides the ability to solve the notorious port-starboard (PS) ambiguity problem of ordinary single-array receivers. More importantly, the PS rejection can be so strong that it allows to unmask targets in the presence of strong coastal reverberation or traffic noise. The theoretical and experimental performance of triplet array beamformers is determined in terms of two performance indicators: array gain and PS rejection. Results are obtained under several typical acoustic environments: sea noise, flow noise, coastal reverberation, and mixtures of these. A new algorithm for (beam space) adaptive triplet beamforming is implemented and tuned. Its results are compared to those of other triplet beamforming techniques (optimum and cardioid beamforming). These beamformers optimize for only one performance indicator, whereas in theory, the adaptive beamformer gives the best overall performance (in any given environment). The different beamformers are applied to data obtained with an LFAS at sea. Analysis shows that adaptive triplet beamforming outperforms conventional beamforming algorithms. Adaptive triplet beamforming provides strong PS rejection, allowing the unmasking of targets in the presence of strong directional reverberation (e.g., from a coast) and at the same time provides positive array gain in most environments.     

一种功率谱相关的基元域近场强干扰抑制方法

针对影响拖曳线列阵声纳系统目标检测性能的两种典型近场强干扰源,由宽带近场阵列模型,提出了基于功率谱相关的干扰抵消方法,通过比较基元域频域信号与干扰波束信号功率谱之间的相似关系,找到与每路基元信号相匹配的干扰分量信号,最后通过频域块自适应滤波算法实现每路基元域信号中的干扰抵消。宽带仿真结果与海试表明,这种方法在强干噪比和低信噪比条件下,比最小方差无失真响应和传统基元域干扰抵消方法在阵增益方面提高约10dB。相比传统基元域干扰抵消方法,这种方法能够实现抵消拖船干扰的同时抵消邻近目标强干扰。     

Analysis of Signal Cancellation Due To Multipath in Optimum Beamformers for Moving Arrays

In this paper, we study the effect of array motion on signal cancellation and interference rejection in optimum beamformers in the presence of multipath with partially or fully correlated sources. First, we show how array motion causes signal decorrelation with a rate that depends on the spacing and directions of the sources. Next, we briefly discuss the signal cancellation and interference rejection behavior of the optimum beamformer in the presence of a correlated interference to motivate the need to decorrelate the desired source from the interference. We then propose an optimally weighted covariance averaging technique to ensure perfect decorrelation of the sources for any given displacement. Computer plots and simulation results are included to support our analysis.     

Spatial processing of signals received by platform mounted sonar

Acoustic signals received by platform mounted sonar arrays can be spatially processed to enhance the detection of targets in the presence of both ambient and platform generated (self) noise. Ambient noise in the ocean, such as that due to distant shipping or biological choruses, are known to be spatially correlated. The platform generated noise will be of near-field origin and may not be received by all elements in the array. In this paper we investigate the performance of the minimum variance distortionless response (MVDR) beamformer and the recently introduced Fourier integral method (FIM) and compare their performances with the conventional beamformer. Real passive sonar data, obtained from a platform mounted sparse linear array of hydrophones, is used to study the performance of the beamformers in a typical sonar environment. It is shown that in the absence of self noise, when the array is accurately calibrated the MVDR beamformer will perform very well, but when sensor gain or phase errors are present the performance of the MVDR beamformer is degraded. Further, the MVDR beamformer is unable to reject the self noise which is not "seen" by the entire array. FIM however seems to perform well and a modified version of FIM, which we call weighted FIM (WFIM), is shown to perform better and is at worst comparable to a well calibrated MVDR beamformer     

Remedying the effects of array shape distortion on the spatialfiltering of acoustic data from a line array of hydrophones

The effects of both small perturbations and large deformations to the array's shape on both conventional and adaptive beamformers are shown for two frequencies: the spatial Nyquist frequency (or design frequency) of the array and a frequency about three times greater. Large shape deformations lead to a decrease in the conventional beamformer's output power for a beam steered in the direction of the signal source, together with an increase in the sidelobe levels (or secondary maxima), while small perturbations in the array shape have little effect. Signal suppression is observed to be far greater for the adaptive beamformer because it is very sensitive to system errors. The imposition of a weight norm constraint on the adaptive beamformer reduces the signal suppression only for small shape perturbations array shape estimation techniques are needed to reduce signal suppression for large shape deformations. The adverse effects of a nonlinear array shape on both conventional and adaptive beamforming are shown to be substantially reduced by applying techniques that estimate the coordinates of the hydrophones prior to beamforming     

基于单矢量水听器四种方位估计方法

单矢量水听器能同时拾取声场的声压和振速信息,可以估计目标方位。根据不同的噪声背景和信号形式,单矢量水听器有多种方位估计方法。平均声强器的处理方法能很好地抗各向同性的非相干干扰;线谱方位估计能有效检测辐射线谱信号的目标,并进行目标方位估计。当宽带信号中存在线谱相干干扰,以及线谱信号被宽带相干噪声干扰时,上述两种方法不能检测目标。为解决这个问题,新提出了直方图和加权直方图两种方法,直方图方位估计法能抗强线谱相干干扰,并能区分含线谱的多目标;加权直方图方位估计法能从宽带相干干扰中检测目标,估计目标方位。并着重介绍了后两种方法的原理,对四种方法进行了计算机仿真,并用海试结果验证了上述结论。