基于成像声呐DIDSON的水域内鱼群数量估计方法*

为准确估计整片水域中的鱼群数量,提出一种利用成像声呐进行数量估计的方法。将成像声呐固定在调查船下,并使波束发射方向与船前进方向一致,通过走航调查方式采集水下信息,对采集的数据进行声呐图像构建、噪声去除、目标提取,其中噪声去除采用固定数据窗口的迭代最小二乘法,目标提取采用基于三倍标准差准则的阈值分割法。接着利用扩展卡尔曼滤波结合最近邻的多目标跟踪算法对图像中的个体目标进行一一计数,同时统计声呐扫描过的水域面积,获得目标个数的平均面密度值,最后结合水域占地面积,估算出整片水域中的鱼群数量。利用该方法实现对滴水湖鱼群数量的估计,通过与人工计数结果比较,发现基于声呐图像处理的数量统计方法具有较高精度,两者的统计值相差约10%。     

平面波经颅超声成像相位校正及散斑跟踪*

准确的脑血流成像对脑功能监测和脑疾病的快速诊断具有重要意义,然而颅骨对超声传播的影响会导致成像质量下降、速度或位移估计不准确等问题。论文采用平面波相干复合结合散斑跟踪方法进行颅内散射目标成像和速度估计,以实现脑血流速度矢量检测;针对颅骨存在导致的超声相位畸变,利用数值仿真和体模实验研究了其对成像及散斑跟踪效果的影响,并采用近似射线声学理论方法进行校正。数值结果表明颅骨的存在造成目标运动速度估计的相对误差达到55%左右,校正后误差降至约12%;体模实验中对目标位移大小和角度估计的平均误差在校正前分别约为16%和28%,校正后均降至1%左右。该研究结果可为超声颅脑疾病诊疗设备的研制提供理论指导和技术支持。     

Multiferroic properties in terbium orthoferrite

Multiferroic properties in a polycrystalline terbium orthoferrite are investigated. Different thermomagnetic behaviors are observed in different magnetic fields, which is attributed to the suppression of the low temperature magnetic phase by an external magnetic field. Further studies reveal that the ferroelectricity originates from the spin configuration below3.5 K. In addition, the magnetic field control of electric polarization and dielectric constant is observed, which suggests a magnetoelectric effect in TbFeO3. The origin of ferroelectricity in this rare-earth orthoferrite is discussed.     

Preparation and characterization of nontoxic magnetic-luminescent nanoprobe

A novel nontoxic,magnetic,and luminescent nanoprobe is prepared by using complex nanoparticles,which are composed of Fe3O4 nanoparticles and Mn-doped ZnS quantum dots(QDs).The nanocomposite probe can provide visible optical and magnetic resonance images simultaneously.Compared with the previously toxic cadmium and mercury based QDs,the superiority of the Mn-doped ZnS QDs is little virulence.The structure and the properties of the particles are characterized by energy dispersive X-ray analysis spectroscopy,X-ray photoelectron spectroscopy,transmission electron microscopy,photoluminescence spectroscopy,and vibrating sample magnetometer.     

Structural and electronic properties of chiral single-wall copper nanotubes

The structural,energetic and electronic properties of chiral(n,m)(3≤n≤6,n/2≤m≤n)single-wall copper nanotubes(CuNTs)have been investigated by using projector-augmented wave method based on density-functional theory.The(4,3)CuNT is energetically stable and should be observed experimentally in both free-standing and tip-suspended conditions,whereas the(5,5)and(6,4)CuNTs should be observed in free-standing and tip-suspended conditions,respectively.The number of conductance channels in the CuNTs does not always correspond to the number of atomic strands comprising the nanotube.Charge density contours show that there is an enhanced interatomic interaction in CuNTs compared with Cu bulk.Current transporting states display different periods and chirality,the combined effects of which lead to weaker chiral currents on CuNTs.     

基于超椭圆拟合的水下小目标分类*

水下小目标分类技术在海底探测、水下考古等方面应用广泛,在实际的水下声图像中,小目标投影产生的阴影区域通常在形状和尺寸方面显著于目标本身产生的亮区,故阴影分析算法对于目标的检测、识别和分类均有重要的研究意义。本文采用超椭圆曲线拟合算法拟合目标阴影区域,通过控制超椭圆函数的几个参数变化,实现不同的超椭圆曲线拟合不同的目标阴影形状,并将控制超椭圆曲线尺寸、形状和位置的参数作为特征向量输入到分类器,通过对比多个分类器得出分类结果,证明了以拟合参数为特征的分类方法有效。     

Photonics-based real-time and high-resolution ISAR imaging of non-cooperative target

Real-time and high-resolution imaging is demonstrated based on field trial detection of a non-cooperative target using a photonics-based inverse synthetic aperture radar(ISAR).By photonic generation and de-chirping of broadband linear frequency modulation signals,the radar can achieve a high range resolution thanks to the large instantaneous bandwidth(8 GHz at the K band),as well as real-time ISAR imaging using low-speed analog-to-digital conversion(25 MSa/s).A small-size unmanned aerial vehicle is employed as the noncooperative target,and ISAR imaging is realized with a resolution far better than those achieved by the previously reported photonics-based ISARs.The capability for real-time ISAR imaging is also verified with an imaging frame rate of 25 fps.These results validate that the photonics-based radar is feasible in practical real-time and highresolution ISAR imaging applications.     

Analysis of space target detection range based on space-borne fisheye imaging system in deep space background

A space-borne photoelectric detection method is proposed based on the long wave infrared (LWIR, 8–14 μm) fisheye imaging system (LWIRFIS) in this paper. The existing detection range equation is modified to calculate the maximum detection ranges of the LWIRFIS for space targets, and the influence of several key parameters is discussed in detail. The results show that, the system maximum detection range increases with the decrease of the half-field angle, the increase of the target area, the rise of the target temperature, the drop of the optics temperature, and the reduction of the system threshold signal-to-noise ratio. The detection range can be improved greatly through taking measures to optimize the latter two system parameters, such as setting up diaphragms, controlling the operating temperature, suppressing the noises by software or hardware methods. This work lays the foundation for the further research of space-borne super-wide field of view (FOV) imaging system, and provides a useful exploration for improving the capability of space situation awareness (SSA) of the space-borne observation platform.     

深空背景弱小目标实时检测算法研究

根据深空背景的特点,提出一种基于FPGA和DSP的检测算法,并设计相应的硬件系统,能对大小为512×512像素、帧频率为40帧/s的视频图像进行实时处理。先在FPGA中用最大中值滤波抑制空间成像噪声,解决了图像预处理运算量大对处理速度要求高的难题,再在DSP中用使用改进的双差分法进行运动目标分割,克服了单差分提取目标轮廓不准的缺点,最后结合候选目标的特征,采用基于逻辑的最近邻关联方法提取目标航迹。试验结果证明该算法满足了深空背景弱小目标实时检测的要求。     

深空背景弱小运动目标检测算法研究

在深入分析监测设备CCD图像特点的基础上,提出了一种深空背景弱小运动目标检测新方法。该算法使用列高通滤波器进行背景抑制;采用序列图像多帧累加增强目标与恒星的对比度,用交叉投影法确定星点区域,提取局部星图,利用局部星图匹配剔除恒星干扰;结合候选目标的特征,采用基于逻辑的最近邻关联方法完成目标检测。结果表明,该算法可满足深空背景弱小运动目标实时检测的要求。     

空间目标天基与地基监视系统对比分析

介绍了空间目标监视系统的发展现状,及其在未来军事作战中的主要应用。简要阐明了美国空间目标监视系统的构成、分布。概括了现有空间监视系统(地基雷达系统、地基深空光电监视系统、天基可见光监视系统、天基雷达系统)的主要技术参数。比较分析了各种监视系统的探测性能、优缺点及应用范围。与其它监视系统相比,天基光学监视系统具有在轨运行、大视场、全天候等特性,它能够满足对空间目标的连续监视、跟踪与精确的特征测量要求。     

Unpredictability of the Wada property in the parameter plane

We show a type of unpredictability of the Wada property in the parameter plane for fixed initial conditions. This property indicates a larger unpredictability of sensitive dependence on parameters except for the riddled parameter sets. We describe some numerical experiments giving evidences of the parameter Wada property for different types of attractors including strange nonchaotic attractors. A scaling exponent is used to characterize sensitive dependence on parameters. We present a qualitative explanation on the occurrence of the Wada property in the parameter plane.     

实时激光三维成像焦平面阵列研究进展

研究了应用于实时激光三维成像的焦平面阵列技术,介绍了目前国际上几种常用的焦平面阵列实现原理与技术特点,并对其优点与不足进行了分析,同时对表征焦平面阵列的主要性能指标以及其对最终成像系统的影响进行了定性分析。根据对现有技术的对比分析,提出基于雪崩光电二极管（APD）阵列和读出电路（ROIC）集成的探测器方案在灵敏度和作用距离等方面具有一定优势,是实现实时三维成像焦平面阵列较为理想的技术。作者认为在未来十几年内,激光三维成像焦平面阵列规模有望超过1 024 pixel×1 024 pixel,像元尺寸可降低到15μm。     

Calculation of the bistatic target strength of a complex multiresonant shell by the finite element method

A method for calculating the bistatic target strength of a complex elastic structure with characteristic linear dimensions of one to ten wavelengths is developed and tested. The proposed method is based on the finite-element approach to modeling the mechanoacoustic properties of the object under consideration, which is complemented with the algorithms of incident plane wave generation and far-field calculation using the Green function of free space. The results of testing the accuracy of the proposed computational method in application to bodies with a simple shape and a known analytical solution are presented. Specifically, a deviation of less than 3 dB from the theoretical value is obtained for the main lobe of the directional pattern of the target strength. The results of calculations are compared with experimental data obtained for a thinwalled reinforced shell used as an example.     

空间目标红外辐射理论计算

建立了空间目标的热平衡方程,利用节点网络法求解其表面温度场分布;然后利用普朗克公式计算了空间目标的红外辐射强度;最后对大气层外某空间目标的表面温度场分布和红外辐射强度分布进行了数值计算。