The port/starboard discrimination based on line-spectrum character in towed line array with hydrophone triplets

The energy ratio of broadband signal is utilized for port/starboard discrimination in towed line array with hydrophone triplets in tradition.It works well in most conditions except for two cases:One is low signal to noise ratio(SNR),and the other is that there is a stronger interference lied on the other side of the line array with approximate bearing angles. A method called line-spectrum character extracting is proposed to discriminate port/starboard for these two cases in this paper,and the SNR needed for port/starboard discrimination is reduced significantly.Simulation and the sea-trial data are analyzed to show that the method is stable and valid,and is expected to be applied in real towed line array sonar.A line-spectrum enhancing technology with lower calculation complexity and stable validity is proposed to ensure the application of this method in lower SNR condition.     

The time-delay estimation method of resolving left-right target ambiguity for twin-line array and its realization

The directivity function of twin-line array sonar can be used to identify left/right target. But the performance is limited by the distance between two lines and also exists the blind area for target identification. A method, which is based on the time-delay estimation between two line arrays, is proposed to identify left/right target. The method is robust with the variation of distance between two line array, the blind area is considerable decreased. The theoretical analysis results and realization method is described. An algorithm base on interpolation method for precisely estimating tune-delay of two line array are derived, therefore the left-right ambiguity problem is solved.     

Research on a port and starboard ambiguity conjugate cancelling method for twin-line array

It is always an important problem in sonar signal processing for towed array to distinguish the target between port and starboard.It is studied in this paper the normalized beam output function for the parallel twin-line array and found a method that can enhance its port and starboard ambiguity suppression by equalizing the amplitude and phase of the beam output from the conventional beam forming.This method gets the weight value by analyzing the normalized beam output function,and then uses the amplitude weight and phase compensation for beam outputs of the twin arrays to cancel the conjugate（mirror） output. Therefore,the port and starboard restrain ratio is maximized.Both the computer simulation and sea trial data showed that this is a simple and practical method,can better enhance the port and starboard restrain ratio,especially when the band is wide.     

Theoretical analysis and experimental research on port/starboard discrimination in towed line array

1 IntroductionThe port/starboard (P/S) ambiguity is one of main drawbacks of a towed line array' Theship must maneuver one time at least to achieve port/starboard discrimination. It is endurablewhen the ship is spying on or tracking the target in long range, but it is unendurable in thecomplicated and varied situation of sea warfare, particularly when surface ship has an attacko f underwater weapons such as torpedoes. So, the research on P/S discrimination has beenriveted special attention.B…     

Beamforming of random line array

In order to solve the problem of the sensor location uncertaintyfor a towed line array,the sample matrix of the signal and time-spacecurve equations of the simulated array shape are presented in this paper.Average beampatterns of randomized processing are given too.The quan-titative results of array shape variation and distortion losses are obtainedfrom the comparison between the computer simulation and the experimen-tal results.In addition,a model for estimating array shape is offered.Anexperiment on dynamical beamforming is carried out.The results showthat SNR improvement of about 4dB may be obtained by dynamic com-pensation for a small array when the distortion is medial and the towspeed is low.     

Array gain of fourth-order cumulants beamforming under typical probability density background

The fourth-order cumulant of zero mean Gaussian distribution noise always equals to zero theoretically.In practice the probability density of noise and reverberation is the key problem to performance of the fourth-order cumulant beamforming technique.In this paper,the array gain functions of the fourth-order cumulant beamforming are deducted considering the instantaneous amplitude distribution of the ambient sea noise and bottom reverberation respectively.And the relationships are determined between array gain and the factors including the number of the array elements,the fourth-order and second-order statistical properties of the noise and reverberation,and the input signal-to-noise ratio.It is also verified that there is a critical signal-to-interference ratio and the fourth-order cumulant beamforming can obtain higher gain and resolution than the conventional beamforming method when the ratio is larger than it.The results of experiment data processing demonstrate that the gain and the resolution of the fourth-order cumulant beamforming coincide with the theoretic.     

The focusing performance with a horizontal time- reversal array at different depths in shallow water

The performance of time-reversal focusing with a horizontal line array at different depths is investigated by normal mode modeling and computer simulation.It is observed that the focusing performance of a bottom-mounted horizontal time-reversal array is much better than that of a horizontal time-reversal array at other depths in shallow water.The normal mode modeling is used to explain this result.The absolute values of the modes at different depths are compared.It is shown that the number of modes whose absolute values close to zero is smaller at the bottom than that at other depths.It means that the horizontal time-reversal array deployed at the bottom can sample more modes,obtain more information of the probe source and achieve better focusing performance.The numerical simulations of time-reversal focusing performance under various conditions,such as different sound speed profiles,and different bottom parameters,lead to similar results.     

Medical ultrasound imaging method combining minimum variance beamforming and general coherence factor

In medical ultrasound imaging field,in order to obtain high resolution and correct the phase errors induced by the velocity in-homogeneity of the tissue,a high-resolution medical ultrasound imaging method combining minimum variance beamforming and general coherence factor was presented.First,the data from the elements is delayed for focusing;then the multi-channel data is used for minimum variance beamforming;at the same time,the data is transformed from array space to beam space to calculate the general coherence factor;in the end, the general coherence factor is used to weight the results of minimum variance beamforming. The medical images are gotten by the imaging system.Experiments based on point object and anechoic cyst object are used to verify the proposed method.The results show the proposed method in the aspects of resolution,contrast and robustness is better than minimum variance beamforming and conventional beamforming.     

Imitating micro-lens array for integral imaging

<正>Integral imaging is a true,three-dimensional(3D) display technology that captures and reconstructs 3D scenes using two-dimensional(2D) micro-lens arrays.The manufacturing technique of micro-lens arrays is complicated and expensive,thus limiting the application of the technology.An imitating micro-lens array for integral imaging is presented in this letter.Imitating micro-lens array is composed of a cheap lenticular lens and a parallax barrier.The relationship of the parameters of the imitating micro-lens array is analyzed and the parameter formulae are deduced.The arrangement of pixels under a cell of the imitating micro-lens array is presented.The imitating micro-lens array is simulated using ASAP software,and the results prove that the designed imitating micro-lens array is effective.A 3D scene is reconstructed on a 3D display that consists of the imitating micro-lens array and a 17-inch flat panel display.     

A passive synthetic aperture phase correction algorithm for the asymmetric twin-line array sonar

A passive synthetic aperture based on phase correction algorithm for solving the port-starboard discrimination problem in the non-aligned towed twin-line array sonar,is de- scribed.This method creates a virtual array through applying the estimated phase correction into one array of twin-line arrays.Because the synthetic virtual array is aligned with the other array in twin-line arrays,the right port-starboard discriminated results can be obtained by array processing based on the new synthetic twin-line array.The effect of proposed method has been shown by simulated and sea-trials results in towed twin-line array sonar.With low extra computational loads,the proposed method is easy to apply to the practice.     

阵形畸变条件下双线阵左右舷分辨性能分析

研究了双线阵在两种阵形畸变(轴向滑移和航向偏差)条件下的左右舷分辨性能,根据双线阵指向性函数的背瓣特性分析了阵形畸变对左右舷分辨性能的影响。理论分析表明,在无阵形畸变的理想阵形情况下,窄带信号的左右舷分辨能力取决于阵间距和信噪比,而对宽带信号,左右舷分辨能力不仅与阵间距和信噪比有关,而且还与接收信号的功率谱密度、处理频段有关。在阵形发生轴向滑移和航向不一致的情况下,在正横方向附近,左右舷分辨性能主要受双线阵的航向差影响,偏离正横方向,较大的轴向滑移会导致左右舷误判。     

基于几何相移模型的双线列阵左右舷分辨技术研究

针对双线列阵克服左右舷模糊问题，将双线列阵认为是由两两阵元为一组的偶极子构成的单线列阵，利用几何相移模型对目标进行左右舷分辨，经过理论分析、仿真实验和湖试实验，指出丁几何相移模型不仅能解决单频情况下的左右舷模糊问题，而且还能解决信号带宽不太宽情况下究竟能到多大相对带宽，取决于所设定的左右舷分辨增益门限)的左右舷模糊问题。该方法经湖试实验得到了很好的验证：在信噪比为5dB时，采用该方法处理时，左右舷分辨差超过7dB。在本文设定的高信噪比条件下，证明了几何相移模型的双线列阵左右舷分辨技术是有效的、可行的。     

矢量水听器线阵和弧线阵抗左右舷模糊性能分析

针对线阵声纳左右舷模糊问题,建立了基于矢量水听器直线阵 和 两种信息处理模式以及标量水听器弧线阵不同布阵方式的抗左右舷模糊性能数学模型,分析了不同布阵方式以及不同信息处理模式的抗左右舷模糊性能,并进行了仿真计算。分析和仿真结果表明,矢量水听器直线阵和标量水听器弧线阵在分辨左右舷性能和观察范围上各有优势。矢量水听器直线阵虽然可分辨左右舷且在作用距离上具有优势,但由于在一定扇面内分辨左右舷是依靠声纳方位历程图的明暗差异,在多目标情况下易造成声纳观察上的干扰;具有一定弧心角的标量水听器弧线阵,可以在更宽的扇面内具有抗左右舷模糊能力,但其以减小观察范围作为代价。     

时延估计与双线阵左右舷分辨

针对双线列阵的左右舷分辨问题，特别是双线阵间距较大时的左右舷分辨问题，文中提出了一种以时延估计为理论基础的左右舷分辨方法，将双线阵的左右舷分辨问题转变成对轴向对称的两路波束信号进行时延估计，然后根据时延值的符号判断出目标所处的左右舷。该方法具有算法简单、对阵形畸变不敏感的优点。经过湖试实验数据分析验证，证明是一种简单、有效、可行的左右舷分辨技术。     

结合盲源分离的非直单线阵多目标左右舷分辨

针对单线阵左右舷模糊问题,提出了结合盲源分离的非直单线阵多目标左右舷分辨算法。该算法首先通过离散傅里叶变换将阵列接收信号离散化为若干个窄带频谱分量,之后对每个频点的窄带数据讲行盲源分离,得到每个频点上各个来波信号的导向向量;然后通过常规波束形成对各个导向向量进行方位谱估计,并根据左右舷抑制比进行单目标左右舷分辨,确定各个频点上的来波方向;最后对所有频点上的来波方向进行聚类,得到各个真实目标的方位,从而实现多目标左右舷分辨。仿真实验中,相比常规波束形成方法(CBF)和最小方差无畸变响应算法(MVDR),该算法更准确地估计出了目标数目,且保持了较快的计算速度;海试数据处理中,该算法排除了目标镜像的干扰,准确估计出了船只目标的轨迹。仿真及海试数据处理均表明,该算法可以分辨真实目标与目标镜像,具有比CBF和MVDR算法更好的左右舷分辨能力。      

基于阵形畸变补偿的多线阵左右舷分辨研究

多线阵可解决单线阵在目标探测中的左右舷分辨模糊问题,但阵形畸变不利于准确实现对目标的左右舷分辨。本文针对多线阵在拖曳过程中出现的典型阵形畸变,定量地分析了其对目标左右舷分辨的影响,并提出了一种基于阵形畸变实时测量补偿来进行目标左右舷分辨的方法,海上实验数据分析结果表明,该方法可实现阵形畸变下的目标左右舷分辨,对于提高拖曳多线阵声纳性能具有参考价值。     

本舰机动左右舷分辨方法研究

针对传统单根线列阵的左右舷分辩问题，经过深入分析，给出了本舰机动左右舷分辨方法中的一些影响因素，并对机动角度和滞后时间得出了定量结论。文中研究的内容对传统拖曳线列阵声纳的左右舷分辨和战术使用具有参考价值。     

Beamforming using spatial matched filtering with annular arrays (L)

A linear array beamforming method for ultrasonic B-mode imaging using spatial matched filtering (SMF) and a rectangular aperture geometry was recently proposed Kim et al., [J. Acoust. Soc. Am. 120, 852-861 (2006)]. This letter extends those results to include circularly symmetric apertures. SMF applied to annular arrays can improve the lateral resolution and echo signal-to-noise ratio as compared with conventional dynamic-receive delay-sum beamforming. At high frequencies, where delay and sum beamforming is problematic, SMF showed greatly improved target contrast over an extended field of view.     

On array design for matched-field processing

Conventional plane-wave beamforming array design guidelines are motivated by the desire to obtain particular beampattern characteristics, such as main lobe width and side lobe levels. These design guidelines are appropriate for arrays employed for beamforming, where a plane-wave signal model is utilized to derive both the array design parameters and the beamforming algorithm. However, matched-field processing utilizes full-field acoustic propagation models to exploit the complexities of ocean acoustic propagation. As a result, there may be more appropriate design guidelines for arrays employed for matched-field processing. In this paper, general guidelines for matched-field processing array design utilizing a normal mode propagation model are proposed. Various line array configurations are evaluated with respect to source localization performance, and the results suggest that arrays designed for matched-field processing should provide a unique representation of each propagating mode along the extent of the array. Further, the empirical analyses support the guidelines suggested by the theoretical analyses and show that arrays which are far from meeting conventional beamforming array design requirements may be more than sufficient for matched-field processing.