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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
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《Waves in Random and Complex Media》2013,23(2):127-143
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
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Research on the acoustic scattering function and coherence properties from rough seafloor based on finite element model 下载免费PDF全文
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
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K. Wu 《Waves in Random and Complex Media》2005,15(2):127-143
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
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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
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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
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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.
Difference scattering field properties between periodic defect particles and three-dimensional slightly rough optical surface 下载免费PDF全文
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
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YE Hongxia & JIN Yaqiu Key Laboratory of Wave Scattering Remote Sensing Information 《中国科学G辑(英文版)》2005,48(6):723-738
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
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Investigation on global positioning system signal scattering and propagation over the rough sea surface 下载免费PDF全文
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
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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
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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