Feature extraction of micro-motion frequency and the maximum wobble angle in a small range of missile warhead based on micro-Doppler effect

Micro-Doppler effect is induced by the micro-motion dynamics of the radar target itself or any structure on the target. In this paper, a simplified cone-shaped model for ballistic missile warhead with micro-nutation is established, followed by the theoretical formula of micro-nutation is derived. It is confirmed that the theoretical results are identical to simulation results by using short-time Fourier transform. Then we propose a new method for nutation period extraction via signature maximum energy fitting based on empirical mode decomposition and short-time Fourier transform. The maximum wobble angle is also extracted by distance approximate approach in a small range of wobble angle, which is combined with the maximum likelihood estimation. By the simulation studies, it is shown that these two feature extraction methods are both valid even with low signal-to-noise ratio.     

基于TF/SF方法的三维复合目标电磁散射FDFD研究

分析三维频域有限差分(FDFD)中通过总场-散射场(TF/SF)边界引入入射波的方法.基于等效原理,在TF/SF边界处设置等效面电磁流,将入射波引入总场区.根据边界附近节点的位置特点,将方程式中的相关节点加入或扣除入射波的相应分量修正FDFD方程式,使得方程式中的各节点满足同为总场或同为散射场的条件.算例结果验证了该方法的正确性.利用FDFD方法计算涂敷吸波材料的复合von Karman型弹头和某导弹模型的双站RCS(radar cross section),数值结果说明该方法是分析复合目标电磁散射问题的一种有效方法.     

Bistatic scattering and depolarization by randomly rough surfaces: application to the natural rough surfaces in X-band

Abstract

The scattering of waves by random rough surfaces has important applications in the remote sensing of oceans and land. The problem of developing a model for rough surfaces is very difficult since, at best, the scattering coefficient σ⁰ is dependent upon (at least) the radar frequency, geometrical and physical parameters, incident and observation angles, and polarization. The problem of electromagnetic scattering from a randomly rough surface is analysed using the Kirchhoff approximation (stationary phase, scalar approximation), the small-perturbation model and the two-scale models. A first major new consideration in this paper is the polarimetric signature calculations as a function of the transmitter location and receiver location for a bistatic radio-link. We calculate the like- and cross-polarized received power directly using the scattering coefficients, without calculating the Mueller matrix. Next, a study of the regions of validity of the Kirchhoff and small-perturbation rough surface scattering models (in the bistatic case) is presented. Comparisons between the numerical calculations and the models are made for various surface rms heights and correlation lengths both normalized to the incident wavenumber (denoted by σ and L, respectively). By using these two parameters to form a two-dimensional space, the approximate regions of validity are then established. The second major new consideration is the development of a theoretical two-scale model describing bistatic reflectivity as well as the numerical results computed for the bistatic radar cross section from rough surfaces especially from the sea and snow-covered surfaces. The results are used to show the Brewster angle effect on near-grazing angle scattering.     

Bistatic scattering and depolarization by randomly rough surfaces: application to the natural rough surfaces in X-band

The scattering of waves by random rough surfaces has important applications in the remote sensing of oceans and land. The problem of developing a model for rough surfaces is very difficult since, at best, the scattering coefficient σ⁰ is dependent upon (at least) the radar frequency, geometrical and physical parameters, incident and observation angles, and polarization. The problem of electromagnetic scattering from a randomly rough surface is analysed using the Kirchhoff approximation (stationary phase, scalar approximation), the small-perturbation model and the two-scale models. A first major new consideration in this paper is the polarimetric signature calculations as a function of the transmitter location and receiver location for a bistatic radio-link. We calculate the like- and cross-polarized received power directly using the scattering coefficients, without calculating the Mueller matrix. Next, a study of the regions of validity of the Kirchhoff and small-perturbation rough surface scattering models (in the bistatic case) is presented. Comparisons between the numerical calculations and the models are made for various surface rms heights and correlation lengths both normalized to the incident wavenumber (denoted by σ and L, respectively). By using these two parameters to form a two-dimensional space, the approximate regions of validity are then established. The second major new consideration is the development of a theoretical two-scale model describing bistatic reflectivity as well as the numerical results computed for the bistatic radar cross section from rough surfaces especially from the sea and snow-covered surfaces. The results are used to show the Brewster angle effect on near-grazing angle scattering.     

扩展性微动目标回波模拟与特征参数提取研究

研究了微动目标的多普勒回波模拟及特征参数提取技术. 提出了一种基于物理光学法和等效电磁流法的扩展性微动目标回波模拟方法. 将在目标坐标系下计算得到的后向散射场通过坐标转换, 成为雷达坐标系下的目标回波, 通过与解析信号模型对比验证方法的正确性. 分析了圆锥与带翼弹头的进动特性, 为获得较好的时频聚集性同时避免交叉项采用S-method方法对获取的回波信号进行时频分析, 分析了不同雷达波入射角度, 不同运动状态及不同几何外形的时频分布特点. 对时频分布图进行逆Radon变换, 将正弦曲线映射到参数空间, 从而获取目标的微动参数. 该研究结合电磁散射与信号处理技术, 通过对典型弹道目标的仿真, 获得一些不同于传统微动模型的结果, 结合电磁散射理论, 对这些现象进行了解释分析. 该研究成果在弹道目标的探测识别领域具有重要的理论与应用价值.     

Bistatic scattering from an anisotropic sea surface: Numerical comparison between the first-order SSA and the TSM models

The first-order small-slope approximation (SSA-1) model is used for numerical predictions of the normalized radar cross section (NRCS) of an anisotropic ocean surface in bistatic configurations for the K_u-band radar frequency. The calculations were made by assuming the Elfouhaily et al. surface-height spectrum for fully developed seas. In the forward-backward case, the SSA-1 presents an agreement with the geometric optics limit of the Kirchhoff approximation results in the near-specular directions where it is well known that the last model works well. In the fully bistatic case, SSA-1 numerical results are compared with those of the two-scale model in several configurations as a function of wind speed, wind direction, incident/scattering angles and for co-and cross-polarization states. Good agreement between the two models is noted in the co-and cross-polarization case with a small difference of about 1-2 dB. But in certain configurations, the SSA-1 model tends to overestimate the radar cross section peak behaviour. This irregularity is discussed and interpreted. The main purpose of this paper is to analyse NRCS predictions based on the SSA-1 model in a fully bistatic configuration.     

大气风场和温度对无线电声波探测系统探测高度影响的数值研究

从声波扰动介质中的电波波动方程出发, 使用时域有限差分(FDTD)方法, 结合声波传播的FDTD 模型, 构建了描述声波和电波相互作用的数值模型, 并运用该模型分析风场和温度对无线电声波探测系统的探测高度的影响. 数值模拟结果表明: 温度与风场剖面的存在改变声波和电波散射回波的传播轨迹; 温度梯度剖面主要影响声波的传播速度, 风场剖面导致作为电波散射体的声波波阵面的偏移, 降低电波散射回波的强度并改变回波路径, 使得接收数据减少, 限制无线电声波探测系统的探测高度; 在强风背景下, 若降低声波散射体高度, 电波散射回波“聚束点”的偏移会有较大的改善, 但同时意味着探测高度的降低. 为了改善风场背景下无线电声波探测系统的探测高度, 可以使用双基地雷达或者增大接收天线面积等方法来实现.     

基于宽带扫频的导弹RCS测量与分析

针对导弹的典型几何外形结构,基于高频散射机理对其散射特性进行了初步分析,包括散射源分布及其散射类型、各散射源散射特性随导弹姿态的变化趋势等。接着,利用宽带扫频RCS测量系统对导弹L、X波段RCS和X波段一维距离像进行了测量,得到了导弹在不同技术条件下的RCS曲线和一维距离像。最后,对测量结果进行了初步分析。测量结果表明：导弹头锥仓与进气道腔体存在较大散射,尤其是进气道壁与弹体之间连接缝隙的散射较为突出;导弹在X波段下的RCS较L波段小,且受姿态变化的影响更为敏感;另外,导弹RCS峰值点并未出现在迎头向,而是偏离迎头向一定角度,尤以X波段下最为明显,偏离角度达20°左右。测量结果为导弹在试验中的应用,包括试验设计、试验结果分析与评估、等效推论等提供了重要的技术依据。     

复杂场景下基于压缩感知的目标电磁散射与成像

研究了处于复杂场景下目标的逆合成孔径雷达(ISAR)成像问题。首先,建立了目标与复杂环境的电磁散射模型,采用计算电磁学的方法仿真得到了目标的雷达回波数据,进而充分考虑了背景噪声对雷达成像质量的影响。研究发现,目标所处的复杂背景会降低ISAR对目标的成像质量。其次,为减小仿真雷达回波数据所需的计算量,提出采用基于压缩感知(CS)的方法来对该场景进行成像,从而极大降低电磁仿真的计算点数。通过实验发现,在CS成像中,采用数据点使用率为0.4时所得到的成像质量可达到采用转台成像质量的效果。因此,采用基于CS的成像方法,可极大降低目标与场景的电磁散射计算复杂度,使得处于真实复杂场景下的目标电磁仿真和ISAR成像研究切实可行。     

New polarimetric signal subspace detectors for SAR processors

Our studies aim at detecting targets embedded in a complex environment for radar applications. This article deals with new polarimetric SAR (synthetic aperture radar) processors based on subspace detectors. These algorithms use models of targets including physical and polarimetric properties of their scattering on the contrary to the isotropic point model that is commonly used. These processors are implemented by computing the corresponding subspaces that contain the relevant responses of the target. We choose for application the detection of targets under forest foliage. The obtained results both on simulated data of realistic targets and real data show the interest of these new processors.     

偏心起爆战斗部随机破片数值仿真

 利用AUTODYN-3D软件和基于Mott破片分布理论的Stochastic随机破碎模型,对破碎型偏心起爆战斗部的破片形成进行了三维数值模拟,对比分析了3种起爆方式下自然破片的飞散特性以及偏心起爆时不同起爆半径随机破片的飞散特性。结果表明：偏心单点和偏心多点起爆在目标区域产生的破片数比中心点起爆分别提高了37.12%和62.86%,且破片质量小,破片的利用率可以提高4.01%~6.08%;偏心单点和偏心多点起爆的平均速度增益为25.95%和28.37%;对于偏心起爆,随着起爆半径的减小,目标区域的随机破片数减小,轴向速度和径向速度也随之减小。     

Reliable approach for bistatic scattering of three-dimensional targets from underlying rough surface based on parabolic equation

A parabolic equation(PE) based method for analyzing composite scattering under an electromagnetic wave incidence at low grazing angle, which composes of three-dimensional(3-D) electrically large targets and rough surface, is presented and discussed. A superior high-order PE version is used to improve the accuracy at wider paraxial angles, and along with the alternating direction implicit(ADI) differential technique, the computational efficiency is further improved. The formula of bistatic normalized radar cross section is derived by definition and near-far field transformation. Numerical examples are given to show the validity and accuracy of the proposed approach, in which the results are compared with those of Kirchhoff approximation(KA) and moment of method(Mo M). Furthermore, the bistatic scattering properties of composite model in which the 3-D PEC targets on or above the two-dimensional Gaussian rough surfaces under the tapered wave incidence are analyzed.     

双基地冰-水界面混响强度的理论预报

针对北极冰层冰水界面具有小尺度粗糙界面的情况,给出由冰层造成的混响平均强度的理论预报公式。首先将北极冰层等效为具有粗糙界面的弹性介质,并且采用小粗糙度微扰理论在精细拟合粗糙度谱的基础上,建立粗糙冰层的三维散射强度模型,然后建立三维双基地声呐几何模型确定有效散射区域,最后给出双基地冰下混响平均强度的估算公式,并在所拟合的粗糙度谱的情况下,利用该预报公式计算双基地声呐配置参数和海冰物理及声学特性对冰下混响强度的影响算例。数值仿真表明该公式能够估算出北极冰下双基地声呐产生的混响平均强度,并且分析出了时延、基线长度等声呐配置参数和冰层声速比、密度比等海冰物理参数会对混响强度造成的影响。声呐的配置参数主要影响散射的有效面积,海冰的物理参数则影响着冰层的散射强度。其中,冰层声速比不仅影响混响强度的大小,还会影响混响强度随时间的衰减速度。      

热防护层覆盖弹体目标雷达散射截面的修正的等效电流近似法和图形计算电磁学法分析

将修正的等效电流近似法与图形计算电磁学法相结合引入到热防护层覆盖弹体目标的电磁散射问题的研究中.应用修正的等效电流近似法对介质和有耗表面进行散射计算,结合图形计算电磁学法,借助于计算机显示技术,将三维目标图形在计算机屏幕上投影,由图形加速卡完成遮挡和消隐工作,利用图形计算电磁学的积分公式,把三维空间的计算转化为二维空间的计算,大大降低了计算时间和复杂度.计算结果表明:当入射波频率较低时,热防护层的厚度不会影响弹体雷达截面值的大小,当频率升高,随着热防护层厚度的增加,弹体雷达截面值不断减小,说明热防护涂层为有耗介质,介电常数的虚部越大其消耗能量的能力越强,弹体雷达截面变化越明显;当热防护层中存在孔隙,热防护层厚度一定,孔隙率越大,雷达截面值越大,孔隙率为零时,雷达截面值最小.当孔隙率相同,热防护层越薄,其雷达截面值越大;当弹体在高空中出现脱粘现象,对弹体的雷达截面值影响不大.     

有限元/边界积分方法在海面及其上方弹体目标电磁散射中的应用

本文将有限元/边界积分方法(FE/BIM)结合区域分解方法引入到粗糙海面及其上方目标 的电磁散射问题的研究中. 由于积分边界可以以任意形状设置在距模型表面任意远的距离处, 故本文采用共形人工边界结合区域分解建模方法截断模型的开放计算区域以减少求解未知量, 在截断区域内部采用有限元方法求解, 而计算区域的边界条件通过边界积分方程方法得到. 通过与矩量法获得的数值计算结果进行比较, 证明了该混合算法及模型处理方法的正确性, 进而研究了海面上方弹体目标的电磁散射特性, 并讨论了其双站散射系数随电磁波入射角度、目标高度、海面风速以及弹体尺寸的电磁散射特性变化情况. 本文结果可用于反演复杂背景下的目标信息及目标探测等领域. 关键词： 电磁散射 粗糙海面 目标 有限元/边界积分方法     

海面中波红外反射率特性研究

基于Cox Munk海面模型,计算了海面对中波红外（3~5 μm）的反射率.利用双站散射遮蔽函数对Cox Munk海面反射率模型进行了修正,数值模拟了反射率随入射角、反射角和风速的变化关系.结果表明,考虑遮蔽效应后,反射率较未考虑遮蔽时的变化更为平缓,且峰值的位置发生变化,峰值明显减小.     

双基地混响平均强度理论及仿真预报

考察远程双基地界面混响,可以仅考察二维问题,其散射区域为一椭圆环带;对于近程双基地界面混响,必须讨论三维模型,其散射元分布在一椭球面上.对二维和三维双基地混响进行理论建模分析,该模型优点是无需使用无线电通信,借助GPS时钟即可同步工作,实现双基地声呐系统的测距及测向,便于双基地声呐系统的集成.推导出二维和三维模型的双基地声压混响理论预报公式.对三维矢量混响作仿真研究,并讨论矢量传感器组合指向性抗混响. 关键词： 双基地混响 声压混响 矢量混响     

基于被动声学的超声速武器脱靶量解算方法

针对武器试验环境日趋复杂,电磁干扰强,且现有主动雷达体制反舰武器矢量脱靶量测量系统存在易受干扰这一问题,该文提出利用多个声学基阵,通过测量超声速武器飞行过程中产生的激波,获取该武器在不同时刻相对声学基阵的方位,进而采用平面相交求解该武器的矢量脱靶量。仿真计算结果表明,当声学基阵测向误差为1°,弹道偏角为45°时,中靶点解算精度优于1.2 m,航向角和俯仰角解算精度优于0.5°,测量精度满足试验评定要求,可为被试武器性能评定提供有效支撑,具有十分重要的军事意义。     

雪层覆盖的粗糙地面与上方矩形截面柱复合电磁散射的时域有限差分法研究

采用土壤介电常数的四成分模型和雪的介电常数模型分别表示实际的地面和雪层的介电特性, 应用指数型分布粗糙面模型和Monte Carlo方法模拟实际的粗糙地面, 运用时域有限差分方法研究了雪层覆盖的粗糙地面与上方矩形截面柱的复合电磁散射问题. 得出了复合电磁散射系数的角分布曲线, 计算了双站复合散射系数随土壤与雪层粗糙度参数、介电参数、 矩形截面柱几何参数、介电参数等的变化情况, 并做了详细分析与讨论. 得到了雪层覆盖的粗糙地面与上方矩形截面柱复合电磁散射特性.     

Ku波段球体目标系的电磁复合散射研究

研究了球形目标之间的电磁相互作用,得到了目标二次散射场的表达式,给出了目标的复合散射场以及双站复合散射截面,并在Ku波段进行了数值仿真.结果表明：目标的尺寸对前向散射和后向散射均有较大的影响,周围目标的影响呈现出一定的周期性,二次散射随着目标间距的增大而减小,周围目标离前向散射方向越近,对前向散射的影响也越大.目标的二次散射场与一次散射场强度之比在10^-4数量级以上.在研究多粒子的相互影响时,周围的粒子可近似看作尺寸一定的粒子.利用所得结果以及坐标变换可以研究三维体系内粒子间的电磁相 关键词： 散射截面 二次电磁散射 电磁相互作用