| Ground penetrating Radar is a kind of near-surface geophysical method using high-frequency electromagnetic waves to determine the laws of composition of subsurface medium. Because of its excellent resolution, simple operation, the advantages of speed, the effectiveness of the method has been validated in various engineering problems. Since introduced to China last century, GPR technology, after years of research and applications in the underground media, the interface characteristic detection has been achieved good results, for example, the detection of the groundwater table, and fault. However, the requirement of the detection of other characteristic of subsurface media has been increasing. For example, resent researches in subsurface pipelines and concrete construction mainly confined to the detection of their buried depth, further researches are need to determine the inclination, obliquity and other characteristic of subsurface materials. Along with the development of the world economy, the advent of a global economy, the demand of resources and environment grows rapidly. Since the 21st century, this trend is particularly evident. As a result, ground penetrating radar, as a shadow geophysical method, is required to be more accurate and obtain more information.In electromagnetic field, polarization is an ancient but new word. People began to study the polarization state of the EM wave and the correlative effect in the early 1950s. Besides amplitude, phase, the Doppler frequency shift, polarization, the fourth character of the radar reflected signal, has begun to be applied. The polarization technology in sounding radar is already quite mature. Since Roberts firstly made a research on the principle of the radar polarization, the application of polarization in GPR has been gradually developed. Based on Jean-Paul Van and Paul L. Stofa's research in 1999, traditional ground-penetrating radar measurements are conducted using two co-polarized antennas both oriented perpendicular to the direction of survey line, such kind of polarization could only give little information of subsurface materials, and the antennas are held parallel to the survey line or cross-polarized to each other have rarely been used. Since the reflection of subsurface materials is related to the angle, only certain respect of subsurface information can be got from traditional GPR antenna polarization measurements, the purpose of the detection is unachieved. Using multi-polarization data acquisition, the extension information of subsurface objects can be got in the use of Alford rotation. Soon Jee Seol, Jung-Ho Kim, Seung-Hwan Yoonho Song and Chung reported in 2001, the received energy will change along with the change of the relative direction of the antenna and the reflector, the direction dependent the GPR response that based on digital simulation experiment can be used to estimate underground cracks and the azimuth of links.In this paper, we made a further research on the GPR polarization measurement response on linear objects. Based on the research of above authors, we concluded that the radar signal received by the receiving antenna was controlled by the extension direction of transmitting and receiving antenna, the mode of the antenna radiation field, and the depolarization of targets. Conventional antenna made use of the two electrical dipole linear antennas of the same attribute, the EM wave transmitted by transmitting antenna was mainly linear polarized wave transmitting along the long axis of the antenna, and the receiving antenna was most sensitive to such kind of linear polarized wave. The antenna radiation mode were the same, so the receiving signal was correlative to the extending direction of the transmitting and receiving antenna, and the depolarization effect of the targets. In the nature world, most targets had the scattering characteristics that sensitive to the polarization. Therefore, the GPR response were different when carrying out the exploration using multiple polarized antennas, the research on the response of the targets could enable us to get a detail knowledge of the extension and direction of the subsurface targets.In the paper, the researches mainly carried out by forward model. A widespread applied EM field numerical method, Finite-Difference Time-Domain (FDTD) was applied to calculate the response of subsurface targets. Its main idea was to discrete the Maxwell rotation equation in time and space domain, then the partial differential equations was replaced by the differential equation, and solve the differential equation, the value of the EM field of each cell could be calculated. It can be used widely, almost the entire electromagnetic and microwave technology in all fields as well as other technological and industrial fields.The GPR polarized measurement models of a group of conductive concrete targets of different extensions were established for the research, the main objective was to study the polarized measurement response of multiple antenna polarization modes to the targets of different directions. From the results of the GPR polarized measurement and the amplitude of the time-domain and frequency-domain wavelet of objects with different directions, we can conclude that: the results of the parallel polarized GPR antennas to the objects of different directions were not satisfied, the depolarization effect of such kind of antenna acquisition was not significant. However, the vertical polarized antenna was extremely sensitive to objects of different directions. After depolarizing, the responses of different objects were quite different. In this paper, with the increasing angle between the objects and the line, the amplitude of the received back scattering field also increased, when the angle got 45 O, the amplitude of the back scattering field got maximum. And when the angle continued to increase, the amplitude decreased, when the angle was 90 O, the amplitude reached almost zero. The research results illuminated that the multiple antenna polarized modes could give more information of the subsurface objects than the conventional radar, using the multiple antenna modes, the subsurface objects of the different direction can be detected.
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