连续波主动声呐的直达波抑制处理方法研究*

针对连续波主动声呐面临的强直达波干扰掩蔽目标回波的问题,该文在双基地配置已知的前提下,提出基于声屏蔽和常规方向零陷的联合抑制方法。即在精确的发射点声屏蔽的基础上,利用常规方向零陷技术减少声源附近方位的能量影响,从而达到更好地消除强直达波干扰的目的。仿真结果表明,在极低的信干比条件下,联合抑制方法比声屏蔽方法、常规方向零陷方法具有更好的干扰抑制性能。该方法可以有效减少连续波主动声呐的直达波的影响,在时间-距离模糊度图上得到清晰的目标位置。     

基于动态阈值匹配追踪的主动声呐直达波抑制方法

双基地声呐中的直达波干扰可以通过重构抵消的方式进行抑制。这种方法需要对直达波信道进行估计,传统的正交匹配追踪算法的收敛速度慢,分步正交匹配追踪等算法在提高收敛速度时牺牲了信道估计精度,导致回波检测能力下降。本文提出一种动态阈值匹配追踪算法估计直达波的信道响应,在提高收敛速度的同时兼顾了信道估计精度。在仿真环境中,达到同样的直达波抑制效果,所提算法与传统正交匹配追踪算法相比,收敛速度显著提升,检测输出的回波强度比分步正交匹配追踪算法高4dB;海试数据处理结果中,所提方法迭代收敛速度较正交匹配追踪算法提升4倍;输出的回波强度比分步正交匹配追踪算法高2dB。     

一个解决声纳系统同频干扰的新思路

多平台联合作战将是未来海上作战的重要形式之一,多部主动声纳的同时存在使声兼容问题十分突出。由于友舰直达波经历的是单程传播,其强度往往比经历了双程传播的目标回波大的多。通过波形设计可以获得相关系数小的声纳波形,虽然可以从一定程度上缓解声兼容问题,但由于获得的增益有限,并不能从根本上解决这一问题。本文通过对常规检测器的修正,引入能量归一化的概念,有效地消除了能量对检测器的影响,从而解决了这一问题。同时本文还提出了与现有声纳信号处理体系相兼容的频域实现方法,使该算法在工程上的实现成为可能。计算机仿真证明,这一方法是正确有效的。     

基于矢量水听器的深海直达波区域声传播特性及其应用

对于深海近水面声源产生的声场, 处于较大深度处的接收器在一定水平距离范围内能接收到直达波. 2014年在某深海海域进行的水声考察实验中, 应用深度为140 m的拖曳声源发射实验信号, 布放在水下3146 m深处的矢量水听器成功地接收到了直达波信号. 本文应用射线理论, 分析了深海直达波区域声场的传播特性, 得出了水平振速与垂直振速的传播损失与声线到达接收点处的掠射角以及收发水平距离之间的关系. 在以上分析的基础上, 提出了一种利用水平振速与垂直振速的能量差估计声源距离的方法, 并结合2014年实验数据对实验中两条航线上8 km范围内的目标声源进行了测距, 测距结果与目标的GPS数据符合得较好.     

声纳中具方向性宽带强干扰的实时抑制方法

声纳中具方向性的宽带强干扰严重影响远处舰船的检测。本文针对此问题,提出一种能实时抑制此类干扰的方法,它以保证干扰方向输出功率最小为约束条件,本文还研究了此方法对目标信号的性能影响情况。最后,通过对海试数据的处理,证明此方法在实践中比较有效。     

浅海双基地有源探测调频信号直达波消除

双基地有源探测常采用长脉宽探测信号以获取更高的时间增益,容易导致回波弱信号被强直达波信号掩蔽而影响回波检测。针对长调频信号直达波的干扰,提出基于分数阶傅里叶变换(FrFT)的直达波消除方法。该方法利用调频信号在时频分布上的稀疏性,通过对接收信号进行分数阶傅里叶变换分离直达波和回波信号然后在变换域对直达波信号进行去除。远程双基地有源探测的收发距离较远,直达波信号经过长距离传播,浅海多途信道的影响不可忽视,因此通过数值仿真分析了浅海声传播对FrFT消除直达波方法的影响。理论和仿真分析结果表明,FrFT对一定时频分布的调频类信号具有足够的分辨力,可以有效在浅海环境中分离和消除直达波干扰。利用2018年的一次海上试验数据,对基于FrFT的直达波消除方法进行了检验,结果表明该方法可有效消除有源探测中的直达波干扰。该方法计算复杂度低,受浅海频散信道影响小,具有很好的稳健性。     

等离子体涨落信号的相关分析——波和不稳定性识别

一、引言 等离子体诊断中的低频涨落,包含了反映带电粒子随机运动和集体运动(如等离子体波、不稳定性过程)的信息。前者的信号呈“噪声”状态,后者则有一定规律。对涨落信号作相关分析,可从涨落信号的“噪声”背景中提取有规信号,并识别出不同来源的涨落信号     

相关哈特曼-夏克波前传感器波前重构新方法

对相关哈特曼-夏克波前传感器的波前重构方法进行了研究,提出了一种基于相邻子图像间相对平移量的波前重构新方法。与常用的基于单一参考子图像的波前重构方法相比,新方法的动态范围有了很大提高。在8×8去4角的子孔径划分下,测量离焦波面时,新方法的动态范围可提高约16倍,子孔径数目越多,动态范围提高的倍数也越高。精度分析表明,两种波前重构方法在8×8去4角的子孔径划分下精度相近,在子孔径数目更多时,相邻子图像处理法的波前重构精度低于单一参考子图像法。     

高光谱图像与稀疏核典型相关分析冷鲜羊肉新鲜度无损检测

羊肉新鲜度受多种因素影响,通常由多个指标来综合评价,常规试验操作复杂不适合在线检测。高光谱成像数据能够反映羊肉新鲜度变化过程中多种成分的变化信息,但是光谱特征提取与评价模型的建立对最终结果影响较大。为了研究高光谱成像与多指标的快速检测羊肉新鲜度的可行性,提出一种稀疏核典型相关分析方法,借助实验室测定的多个标准值,研究多指标的羊肉新鲜度无损检测。采集了70个代表各级新鲜程度的羊肉样本400~1 000 nm高光谱图像,采用实验室方法测定了挥发性盐基氮(TVB-N)和菌落总数(TAC)标准值,选择感兴趣区域(ROIs)提取代表性光谱图像,利用所提出的特征提取方法提取光谱特征信息,并按照3:1划分校正集和预测集,利用三层神经网络进行分类识别试验。结果表明,新鲜度等级分类总体精度(OA)为0.939 3,Kappa系数为0.906 0,均方根误差(RMSEC)为0.297。研究表明,所提出的多指标光谱特征提取方法可用于快速无损检测羊肉新鲜程度,为采用高光谱成像综合多个新鲜度检测指标,改善由于单一检测指标造成评价模型的适用性和鲁棒性提供了基础。     

子空间判决分析的强干扰抑制

针对海洋中存在的强干扰和环境噪声导致水下目标方位估计算法性能剧烈下降的问题,提出了一种子空间判决分析的强干扰抑制方法(SSJ),可实现多个强干扰下的目标方位估计。根据常规波束形成粗估的目标角度区间,利用目标-干扰-噪声子空间与导向矢量的相关性,设置判决项和估计合适的判决阈值来分离和抑制样本协方差矩阵中的非目标信息,降低干扰和噪声的输出功率,同时提高输出信干噪比,为增强阵列的目标方位分辨能力提供方法支撑。仿真和海试数据处理结果显示,SSJ方法可抑制目标角度区间外的强干扰和噪声,明显降低了干扰的输出功率和目标主瓣附近的旁瓣级,提高了目标方位角度的分辨力。相比于现有的子空间干扰抑制方法,所提方法具有更加稳健的干扰抑制能力。     

Kernel-aligned multi-view canonical correlation analysis for image recognition

Existing kernel-based correlation analysis methods mainly adopt a single kernel in each view. However, only a single kernel is usually insufficient to characterize nonlinear distribution information of a view. To solve the problem, we transform each original feature vector into a 2-dimensional feature matrix by means of kernel alignment, and then propose a novel kernel-aligned multi-view canonical correlation analysis (KAMCCA) method on the basis of the feature matrices. Our proposed method can simultaneously employ multiple kernels to better capture the nonlinear distribution information of each view, so that correlation features learned by KAMCCA can have well discriminating power in real-world image recognition. Extensive experiments are designed on five real-world image datasets, including NIR face images, thermal face images, visible face images, handwritten digit images, and object images. Promising experimental results on the datasets have manifested the effectiveness of our proposed method.     

一种简单的干涉光路

介绍了用反射镜和立方棱镜实现两束光相干涉的光路。     

Recovery of spectral data using weighted canonical correlation regression

The weighted canonical correlation regression technique is employed for reconstruction of reflectance spectra of surface colors from the related XYZ tristimulus values of samples. Flexible input data based on applying certain weights to reflectance and colorimetric values of Munsell color chips has been implemented for each particular sample which belongs to Munsell or GretagMacbeth Colorchecker DC color samples. In fact, the colorimetric and spectrophotometric data of Munsell chips are selected as fundamental bases and the color difference values between the target and samples in Munsell dataset are chosen as a criterion for determination of weighting factors. The performance of the suggested method is evaluated in spectral reflectance reconstruction. The results show considerable improvements in terms of root mean square error (RMS) and goodness-of-fit coefficient (GFC) between the actual and reconstructed reflectance curves as well as CIELAB color difference values under illuminants A and TL84 for CIE1964 standard observer.     

Direct correlation function of the hard-sphere fluid

Two analytic approximations for the direct correlation function of a hard-sphere fluid are considered. The first follows from a generalization of the Percus–Yevick result in d dimensions, whereas the second arises in the Rational Function Approximation (RFA) method. Both approximations require the equation of state of the hard-sphere fluid as input. The results, derived after use of the Carnahan–Starling and the Padé 4 Ripoll, MS and Tejero, CF. 1995. Molec. Phys., 85: 423[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar],3 Wertheim, MS. 1963. Phys. Rev. Lett., 10: 321 J. Math. Phys. 5, 643 (1964); E. Thiele, J. Chem. Phys. 39, 474 (1963).[Crossref], [Web of Science ®] , [Google Scholar] equations of state in both approaches, are compared with simulation data. The comparison shows that the first approximation is rather accurate in the region inside the core, but inherits the limitation of the Percus–Yevick theory for distances beyond the hard-sphere diameter. On the other hand, the results of the RFA method are also accurate inside the core and capture well the initial part of the tail beyond the hard-sphere diameter, but fail to account for the subsequent oscillations observed in the simulations. Other merits and limitations of the two approaches are reported.     

An enhanced common path interference optic measurement system for refractive indices and thickness

This study proposes a common path interference optical system for the measurement of refractive indices and thickness of uniaxial crystal material. The measurement system comprises an accurate Mach–Zehnder laser interferometer, a single-axis rotary stepping motor, and a computer. The laser interferometer is composed of a single-frequency He–Ne laser, two-beam splitters and two reflectors. The Mach–Zehnder laser interferometer measures the optical length difference by using its linear measurement accuracy. The proposed solution procedure enables both the refractive indices and the thickness of the optical waveplate to be obtained. The proposed design differs from conventional designs in that it does not use a heterodyne modulator with a lock-in technique. It is shown that the refractive indices and thickness of the tested optical elements can be measured rapidly and accurately.     

迈克耳孙干涉仪中附加光程差对干涉图样影响的讨论

用迈克耳孙干涉仪做物理光学实验,教学中出现了在常规中不能出现的奇异现象,本通过分析仪器中的附加光程差,对干涉图样形成的原因作了定性解释,并得出结论。     

用等值宽度法测量fs脉冲宽度

本文提出利用等值宽度测量fs光脉冲持续时间的方法.给出了脉冲形状为sech~2 (t/T)、exp(-2t~2/T~2)和exp(-2|t|/T)的干涉相关曲线上包络与相应二阶强度相关曲线半宽度等值的位置,它们分别是3.984、4.875和4.928.定义了两种相关测量的临界延迟速度.理论分析与实验结果符合得很好.所得结果表明,该测量方法可将常规超短脉冲相关测量的时间分辨率提高几倍至几十倍.     

Optical path difference evaluation of the polarization interference imaging spectrometer

The optical path difference (OPD) of the static polarization interference imaging spectrometer and wide-field-of-view polarization interference imaging spectrometer are calculated and analyzed, simultaneously. The analysis results show that the actual total OPD contains two parts, the Savart polariscope introduces the first part, and the second part is introduced when imaging lens reunites two beams in its focal plane. Since the first part OPD accounts for about half of the actual total OPD, it has influences on the resulting spectrum and thus cannot be neglected. The influences of the uniaxial crystal dispersion on the OPD and resulting spectrum are analyzed, and the results show that the OPD decreased with the wavelength, the spectral resolution increased with the wavelength. There are no fixed spectral resolution over the entire detection spectral region, and the spectral resolution would become worse with the increase of the wavelength.     

一种采用脉冲串的自适应有源干扰抵消器

在许多应用中，周期性干扰是由旋转的机械设备所产生的。一个周期性信号可以与一个特殊形式的周期性的脉冲串完全相干。本文提出了一种采用脉冲串的自适应有源噪声抵消器(AANC)来抵消周期性干扰，这种抵消器产生一个与干扰信号相同步的周期性的单位脉冲串作为参考输入。将这种有源噪声抵消器和Delayed-X LMS算法相结合，可以大大地减小运算量，并且也可以保证良好的收敛特性。理论分析和计算机仿真验证了本文的结果。