基于UWB源的二维地电模型FDTD正演模拟

THE FDTD FORWARD MODELING OF TWO DIMENSION GEOELECTRICITY BASED ON UWB SIGNAL

采用FDTD(Finite Difference Time Domain)数值模拟方法及CPML(Convolutional Perfect MatchedLayer)吸收边界条件,建立了空气—地下半空间的简单地电模型,分别以UWB(Ultra Wide Band)信号和宽带信号作为发射源,模拟了不同形状(方形、圆形)异常体模型的正演情况。结果表明UWB信号作为发射源的正演模型、能量图能清晰地反映异常体的位置和形状,能区分异常体的电性特征;而宽带信号作为发射源的正演模型只能大致看出空气土壤分界面,不能较好地分辨出异常体,其相应的能量图具有不规则的多个脉冲,也不能反映异常体的形状位置特征。方形、圆形组合模型的正演结果进一步体现了超宽带信号高分辨率的特点,为更好地识别地下异常体,以及地电模型的反演提供了有利的依据。另外,CPML吸收边界条件的应用消除了入射到截断边界处波的反射。

This paper applies the numerical simulation method of FDTD （Finite Difference Time Domain）, and the absorption boundary condition of convolutional perfect matched layer, and builds up the air-underground half-space simple geoelectricity models. We respectively take the UWB（Ultra Wide Band） signal and the wide band signal as the transmitting source, simulates the forward models with anomalies of different shape （square, circle）. The results of simulation indicate that the forward models figures and energy figures with UWB signal as the transmitting source clearly reflect the position and sharp of anomalies. And also distinguish the difference of electric properties of anomalies. While the forward models figure and energy figure with wide band signal as the transmitting source only to be able approximately to see the air-soil minute contact surface, cannot distinguish the anomalies, and its corresponding energy figures have many irregular pulses which can＇t reflect the shape and position characteristics of anomalies. The forward modeling with both square and circle regarding UWB as the source further to manifest the high resolution characteristic of UWB signal, and provide advantageous basis to better underground anomaly recognition and the dielectric model inversion. The absorption boundary condition of convolutional perfect matched layer greatly eliminates the wave reflection caused by incidence to the boundary in the entire simulation.