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1.
依据基尔霍夫近似,推导出一维高斯随机粗糙面四阶统计特性解析式,并获得脉冲波入射下粗糙面双点双频四阶矩互相关函数.数值计算不同入射角,不同高度起伏和相干长度,随机粗糙面双点双频四阶矩互相关函数随相干频谱带宽频差,散射角的变化情况.计算结果表明,高度起伏和相干长度对粗糙面散射四阶统计特的影响很大,粗糙面越光滑,在镜反射方向有最大的四阶矩散射峰值和小的相关带宽.随着粗糙度增加,随机粗糙面脉冲散射的四阶矩的相干分量减弱,展宽现象明显;而相干带宽频差越大,四阶矩衰减越快. 关键词: 四阶矩统计特征 双点双频互相关函数 随机粗糙面 脉冲波散射  相似文献   

2.

The propagation of a transient electromagnetic pulse over irregular terrain is considered. We model the wave propagation using the parabolic wave equation, which is valid for near-horizontal propagation. We model the effect of scattering from the rough terrain by introducing a surface-flattening coordinate transform. This coordinate transform simplifies the boundary condition of our problem, and introduces an effective refractive index into our wave equation. As a result, the problem of propagation over an irregular surface becomes equivalent to the problem of propagation through random media. The parabolic equation is solved analytically using the path integral method. Both vertically polarized and horizontally polarized signals are treated. Cumulant expansion is introduced to obtain an approximate expression for the two-frequency mutual coherence function. From the mutual coherence function, spatial and temporal dependence of the propagating signal can be determined. It can be shown that scattering from the irregular surface can cause broadening of the transient signal. This can have a significant impact on the performance of radio communication systems.  相似文献   

3.
雷波  杨益新  马远良  陈东旭 《中国物理 B》2016,25(12):124312-124312
Acoustic scattering from a rough sea bottom is recognized as a main source of reverberation. In this study, scattering properties from a layered bottom were exploited based on the finite element model. The scattering strength and loss from the layered rough seabed were investigated by ensembling the realizations of rough interface. They were found to be dependent on the thickness of sediment, and interference was significant in the case of thin sediment. Through verification of the finite element model, the scattering loss could be evaluated using the Eckart model with a proper sound speed in the thick sediment. The multiple scattering effect on the sound field was also exploited. It revealed that the effect depended strongly on the bottom type.  相似文献   

4.
The propagation of a transient electromagnetic pulse over irregular terrain is considered. We model the wave propagation using the parabolic wave equation, which is valid for near-horizontal propagation. We model the effect of scattering from the rough terrain by introducing a surface-flattening coordinate transform. This coordinate transform simplifies the boundary condition of our problem, and introduces an effective refractive index into our wave equation. As a result, the problem of propagation over an irregular surface becomes equivalent to the problem of propagation through random media. The parabolic equation is solved analytically using the path integral method. Both vertically polarized and horizontally polarized signals are treated. Cumulant expansion is introduced to obtain an approximate expression for the two-frequency mutual coherence function. From the mutual coherence function, spatial and temporal dependence of the propagating signal can be determined. It can be shown that scattering from the irregular surface can cause broadening of the transient signal. This can have a significant impact on the performance of radio communication systems.  相似文献   

5.
Extinction theorem was used to deduce the first order scattering cross-section including the double scattering effects for the fluid-fluid rough surface. If the double scattering effects are neglected in the present method, the scattering cross-section agrees with the result obtained by the perturbation method based on Rayleigh hypothesis. Calculations of scattering strength were carried out, and comparisons with the first-order perturbation method based on Rayleigh hypothesis were also done. The results show that double scattering effects are obvious with the increase of the root mean square of surface height and the grazing angle when the valid condition k 1 h < 1 is satisfied. Supported by the National Basic Research Program of China (Grant No. 2005CB422307)  相似文献   

6.
扩展面光源如太阳光与激光光源有明显的差异,因此它们照射到随机粗糙柱面后的散射特性也不同。利用随机面元模型,详细分析了刚性随机粗糙柱形表面的激光散射特点,建立了实用化的随机粗糙柱面激光散射理论模型,并给出了正入射时几种情况下的激光散射图像。结果表明,不管哪种情况,正入射时柱面的激光后向散射都很强,而偏离后向的激光散射分布与表面的粗糙度及照射光斑与柱面直径的关系等有关。  相似文献   

7.
随机粗糙柱面的激光散射特性研究   总被引:1,自引:5,他引:1       下载免费PDF全文
 扩展面光源如太阳光与激光光源有明显的差异,因此它们照射到随机粗糙柱面后的散射特性也不同。利用随机面元模型,详细分析了刚性随机粗糙柱形表面的激光散射特点,建立了实用化的随机粗糙柱面激光散射理论模型,并给出了正入射时几种情况下的激光散射图像。结果表明,不管哪种情况,正入射时柱面的激光后向散射都很强,而偏离后向的激光散射分布与表面的粗糙度及照射光斑与柱面直径的关系等有关。  相似文献   

8.
依据高斯波束体目标散射特征,研究了粗糙体目标高斯波束散射场量的互相关函数统计特征。在激光波束入射下,通过数值方法讨论圆球类目标、不同半径、不同材料、不同入射波束极化等条件下,散射场量的互相关函数随散射角变化情况。数值计算结果表明:金属薄膜材料比非金属镀漆材料互相关函数量值要大,金属材料球体目标的后向散射互相关函数值较大,而非金属镀漆材料球体互相关函数值较小。材料表面的粗糙度和目标尺寸对互相关函数影响较大,而入射光的极化方式对相关函数有影响但影响较小。  相似文献   

9.
张民  吴振森 《物理学报》2007,56(10):5937-5944
根据随机介质波传播理论,开展脉冲波在星际空间等离子体介质中的传播特性的分析方法研究.在强起伏条件下,推导双频互相关函数的二阶矩和四阶矩方程,利用不同电子密度模型,计算双频衍射强度相关函数和闪烁指数,并应用到闪烁的动态谱观测和相关分析中,得到自相关图谱、相关带宽和相关时间等闪烁特征参数,为脉冲在等离子体中的传输特性的分析,提供必要的理论基础.  相似文献   

10.
陈敏  肖体乔  徐洪杰 《物理学报》2003,52(11):2807-2810
用Monte-Carlo方法模拟了超短THz脉冲在随机散射介质中的传播.根据Mie理论计算出随机散射介质的散射系数和各向异性因子,研究了随机散射颗粒及介质厚度的大小对透射脉冲的影响.结果表明在Mie散射范围内,在相同的浓度下,颗粒尺寸越小,散射介质越厚,THz散射越严重,对透射脉冲的影响越大.散射同时降低了THz脉冲在随机散射介质中的成像分辨率. 关键词: 超短THz脉冲 随机散射介质 Mie理论 Monte-Carlo方法  相似文献   

11.
The statistical distribution of natural phenomena is of great significance in studying the laws of nature. In order to study the statistical characteristics of a random pulse signal, a random process model is proposed theoretically for better studying of the random law of measured results. Moreover, a simple random pulse signal generation and testing system is designed for studying the counting distributions of three typical objects including particles suspended in the air, standard particles, and background noise. Both normal and lognormal distribution fittings are used for analyzing the experimental results and testified by chi-square distribution fit test and correlation coefficient for comparison. In addition, the statistical laws of three typical objects and the relations between them are discussed in detail. The relation is also the non-integral dimension fractal relation of statistical distributions of different random laser scattering pulse signal groups.  相似文献   

12.
The difference field RCS (d-RCS) has been defined to analyze the scattering from the target above a rough surface. The electric field integral equations (EFIEs) of the difference induced currentJ sd on the rough surface, the induced electric currentJ o and magnetic currentK o on the dielectric target under a TE wave incidence are derived. A small portion of the rough surface towards the target along the specular direction is taken to compute the scattering contributionE s0 from the rough surface towards the target, which improves the computation speed. A numerical iterative approach is developed to solve the EFIEs and bistatic d-RCS. The surface length for iterations is dependent on the scattering angle and discussed for comparison with Johnson’s method. Using the Monte-Carlo method to generate the Pierson-Morkowitz (P-M) ocean-like rough surface, bistatic d-RCS of the dielectric target, e.g. a cylinder or a square column, above the rough surface is numerically simulated. The induced electric and magnetic currents on the dielectric target and the difference induced current on the rough surface are numerically discussed.  相似文献   

13.
葛城显  吴振森  白靖  巩蕾 《中国物理 B》2017,26(6):64201-064201
Based on the practical situation of nondestructive examination, the calculation model of the composite scattering is established by using a three-dimensional half-space finite difference time domain, and the Monte Carlo method is used to solve the problem of the optical surface with roughness in the proposed scheme. Moreover, the defect particles are observed as periodic particles for a more complex situation. In order to obtain the scattering contribution of defects inside the optical surface, a difference radar cross section is added into the model to analyze the selected calculations on the effects of numbers, separation distances, different depths and different materials of defects. The effects of different incident angles are also discussed. The numerical results are analyzed in detail to demonstrate the best position to find the defects in the optical surface by detecting in steps of a fixed degree for the incident angle.  相似文献   

14.
1 Introduction Electromagnetic scattering from the target above or beneath a rough surface has at- tracted much interest during recent years, because of extensive applications to radar surveillance, target detection, ground radar probing, and so on[1―3]. In order to numeri- cally simulate scattering from composite model of the target and underlying rough sur- face, some fast numerical methods, such as general forward backward method and spec- trum acceleration algorithm (GFBM/SAA)[4,5], fin…  相似文献   

15.
王晓冰  梁子长 《物理学报》2012,61(12):124104-124104
采用快速远场近似的降秩电磁流迭代法计算目标与粗糙水面的复合散射, 并进一步采用粗糙面分区的多进程并行迭代算法提高其计算速度, 分析了降秩电磁流迭代法对散射结果的影响, 表明该方法可用于近场复合散射问题的计算; 对平板目标与水面间的复合散射进行了计算, 计算结果与快速多极子方法(MLFMM)结果符合较好, 验证了该算法的有效性. 同时, 利用造波水池开展了目标与水面近场复合散射的模拟实测, 测试与计算结果趋势较为一致.  相似文献   

16.
杨超  郭立新  吴振森 《中国物理 B》2010,19(5):54101-054101
This paper is devoted to the study of polarization properties, scattering properties and propagation properties of global positioning system (GPS) scattering signal over the rough sea surface. To investigate the polarization and the scattering properties, the scattering field and the bistatic scattering coefficient of modified Kirchhoff approximation with using the tapered incident wave is derived in detail. In modeling the propagation properties of the GPS scattering signal in the evaporation duct, the initial field of parabolic equation traditionally computed by the antenna pattern with using fast Fourier transform (FFT) is replaced by the GPS scattering field. And the propagation properties of GPS scattering signal in the evaporation duct with different evaporation duct heights and elevation angles of GPS are discussed by the improved discrete mixed Fourier transform with taking into account the sea surface roughness.  相似文献   

17.
张宇  张晓娟  方广有 《物理学报》2012,61(18):184203-184203
首先建立大尺度分层介质粗糙面散射的物理模型, 基于Stratton-Chu积分方程和Kirchhoff近似导出了粗糙面散射场的计算公式. 采用高斯随机粗糙面来模拟实际的分层介质粗糙面, 通过数值计算得到了正下视单站雷达接收到的后向散射回波. 理论推导了散射场强度与表面粗糙度之间的定量关系, 并从数值仿真的角度分析了表面和次表面的粗糙度对散射回波的影响, 给出了散射场随粗糙度变化的曲线. 最后考察了分层介质的电特性参数(介电常数和电导率)对分层粗糙面散射场的影响, 并对计算结果做出了分析.  相似文献   

18.
郭立新  王运华  吴振森 《物理学报》2005,54(11):5130-5138
研究了二维导体微粗糙面与其上方金属平板复合电磁散射特征.应用互易性原理使求解二次散射场简化为求解包含平板上的极化电流和微粗糙面散射场的积分方程,从而降低了求解难度.应用物理光学近似和微扰法分别求解了平板上的极化电流和粗糙面的电磁散射场,得到了复合散射截面计算公式并进行了数值计算.尤其对该复合模型后向耦合电磁散射结果进行了详细分析和讨论. 关键词: 互易性原理 复合电磁散射 微粗糙面 平板  相似文献   

19.
丁锐  金亚秋 《物理学报》2011,60(12):124102-124102
提出一种解析的随机泛函方法(SFA),计算导体Gauss粗糙面上三维导体目标的复合电磁散射.推导粗糙面的随机Green函数,用一种新的四路径模型描述面体复合散射机理,用SFA求解双站差场雷达散射截面.以导体球目标为算例,与其他数值计算方法比较后验证了SFA的有效性与准确性,同时讨论了粗糙度、体目标尺寸以及距离粗糙面高度等参量变化对结果的影响,给出复杂形状体目标的双站差场雷达散射截面的空间角分布. 关键词: 随机泛函方法 粗糙面随机Green函数 差场雷达散射截面 面体复合散射  相似文献   

20.
双尺度动态分形粗糙海面的电磁散射及多普勒谱研究   总被引:14,自引:0,他引:14       下载免费PDF全文
利用更为符合海面实际散射场计算的双尺度法分析并计算了一维动态分形粗糙海面的后向散射截面,同时与微扰法有关结果进行了比较.研究了动态分形海面后向散射信号的多普勒谱分形特征,分析了不同极化状态下后向散射截面和多普勒谱谱宽随入射角及分维的变化规律,最后详细讨论了多普勒谱中心频率与海面Bragg谐振频率间的关系. 关键词: 双尺度模型 分形海面 电磁散射 多普勒谱  相似文献   

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