Study on the Characteristics of Composite Electromagnetic Scattering From Soil Surface and Combinatorial Target Placed on It
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摘要: 为了满足置于粗糙面之上组合目标测量和检测的需要，该文分别采用Dobson半经验模型和电介质复介电常数公式表示土壤介电常数的实部和虚部，应用指数型分布粗糙面和Monte Carlo方法模拟实际的土壤表面。通过与矩量法得到的计算结果比较，验证了时域有限差分(FDTD)方法计算粗糙面与目标复合散射问题的有效性，进而运用该方法研究了土壤表面与置于其上组合目标的复合散射，得出了复合散射系数的角分布曲线。结果表明：复合散射系数随散射角振荡地变化，在镜反射方向处发生散射增强效应；土壤表面高度起伏均方根越大，复合散射系数越大；相关长度越大，复合散射系数越小；湿度越大，复合散射系数越小；组合目标尺度、介电常数、入射角对复合散射系数影响比较复杂。该文结果可用于求解地、海粗糙面与置于其上任意目标的复合电磁散射问题，与其它数值计算方法相比较，采用时域有限差分方法既可获得较高的准确性，同时又可减少计算时间和内存占用量。Abstract: In order to meet the needs of measuring and detecting combinatorial target placed on the rough surface, Dobson semi-empirical model and dielectric complex permittivity formula are used to represent the real and imaginary parts of the soil dielectric constant, the soil surface is simulated with the model of exponential distribution and Monte Carlo method. The strategy of the Finite Difference Time Domain (FDTD) method for calculating the composite scattering from rough surface with target and the modeling method are presented with their validity evaluated by the method of moment, then the composite scattering of soil surface and combinatorial target placed on it is studied by this method, the angular distribution curve of the composite scattering coefficient is obtained. The results show that the composite scattering coefficient oscillates with the scattering angle, and the scattering enhancement effect occurs in the mirror reflection direction; the larger the root mean square of the fluctuation of soil surface, the larger the composite scattering coefficient; the larger the correlation length, the smaller the composite scattering coefficient; the larger the soil moisture content, the smaller the composite scattering coefficient; the influence of the scale and dielectric constant of combinatorial target, incident angle on composite scattering coefficient is complex. The results obtained in this paper can be used to solve the composite electromagnetic scattering from rough land surface and rough sea surface with any target placed on it. Compared with other numerical methods, the finite difference time domain method can not only obtain higher accuracy, but also reduce the calculation time and the amount of memory occupying.
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