Basic studies on cavity and buried object detection from borehole radar data by using FBTS method

课题组开发了一种利用时域微波数据重建高对比度二维和三维有损物体的方法。在研究期间，我们开展了以下研究活动。(1)考虑了偶极子天线的长度，利用模拟数据成功地同时重建了三维有耗物体的相对介电常数和电导率。(2)将三维FBTS方法应用于由偶极天线激发和接收的实验数据重建二维无损圆柱体。为了加快重建速度，将接收到的数据转换为数据，就像通过理想偶极子发送和接收一样。因此，利用FDTD方法可以同时对一个发射机和多个接收机进行正演模拟，而不受接收偶极子天线之间耦合的影响。然后将变换后的数据用于重建。重构结果与已知物体的介电常数、形状和大小一致。(3)将遗传算法应用于野外常用变送器探地数据的偏移速度分析。由速度分析得到的相对介电常数分布，得到了含水率的分布。这与通过其他方式获得的地质信息是一致的。

The research group has developed a method for reconstructing 2D and 3D lossy objects with high contrast by using time-domain microwave data.During the term of research we have carried out following research activities. (1)Simultaneous reconstructions of relative permittivity and conductivity of a 3D lossy object have succeeded from simulated data by taking the length of dipole antennas into account. (2)The 3D FBTS method has been applied to reconstruct a 2D lossless cylinder from experiment data excited and received by dipole antennas. In order to speed up the reconstruction, the received data are transformed into the data as if transmitted and received by ideal dipoles. Thus the forward simulation by using FDTD method for one transmitter and multiple receivers can be carried out simultaneously without the influence of coupling among the receiving dipole antennas. Then the transformed data are used in reconstruction. Reconstructed result is consistent with the known object both in the value of permittivity, and in the shape and size. (3)Migration velocity analysis by using genetic algorithm has been applied to field common transmitter ground penetrating data. From the distribution of relative permittivity obtained from velocity analysis the distribution of water content has been obtained. It is consistent with geological information obtained by other means.