Detection Of Ice Layer Fracture By Full-polarimetric Airborne Ground Penetrating Radar

The research of fracture of ice layer is an important content in glaciology, the distribution, size and style of various fractures are also important factors which influence ice work and research. But because of the restriction of environment condition, we can not detect by manpower or can not guarantee the security during the work, so it is an efficient method that using airborne GPR to detect the fracture of ice layer. Airborne GPR shows great advantage for coping with objective condition, for example regions which are covered by large area and large thickness vegetation, rugged regions and regions such as battlefields, glaciers and so on which have serious threat for the safety of staff. Hanging traditional GPR antennas or deliberately developed antennas on airborne mobile platform, such as airplanes, fire ballons and so on which fly on a certain height. Firstly, a transmitting antenna emits electromagnetic wave transmitting in a form of geometric spreading in the air. Secondly, entering underground after coupling with ground, then happening reflection, refraction, scatter, et al on the border of different materials. Finally, a receiving antenna will receive a part of returned power and record. According to analyze the received signal, we can deduce the condition of the underground.Using traditional GPR, we will lose plenty of polarized information of reflectors because of its singular polarized transmitting and receiving form. For space traces changing with time, polarized GPR effectively describes the space traces of different directions and strengths which produced by electromagnetic field vector endpoint. Different Polarizations reflect different properties of target area, we can obtain more information by applying multipolar mode. It is significant and helpful for information acquisition of object and GPR data processing and interpretation that using polarized information reasonably and more important target scattering information included in the polarized information has enormous potential for resisting source interference and noise interference, filtering and amplifying object signal and detecting and recognizing objects(surface roughness, symmetry and orientation). When the antennas are parallel to survey direction, we call it H polarization, when the antennas are perpendicular to survey direction, we call it V polarization. When the transmitting and receiving antennas are all parallel to survey direction, we call it HH polarization, when the transmitting and receiving antennas are all perpendicular to survey direction, we call it VV polarization, when the transmitting or receiving antenna is parallel tosurvey direction, and another transmitting or receiving antenna is perpendicular to survey direction, we call it HV or VV polarization. HH and VV polarizations are called co-polarization mode, HV and VH polarizations are called cross-polarization mode. In this paper, we apply HH, VV and VH polarizations, further, develop a set of full polarimetric GPR system based on above antenna polarization modes, we can get better structure and geometry information by conducting Pauli decomposition for the results of above three polarization.According to above condition, in this paper, we use a set of airborne polarimetric GPR system which is composed of Agilent Field Fox0N9925 A portable network analyzer and computer control unit, this system includes Vivaldi antennas, portable network analyzer and laptop. First, we design data collecting interface through Lab VIEW on laptop. Second, the step frequency pulse signal is generated by portable network analyzer with a working frequency of 30KHz-9GHz and emit through a antenna with bandwidth 1.2GHz-8.5GHz. Final, data is transported to data collecting interface on the laptop through the LAN interface from the portable network analyzer, then displayed and saved on the computer. Because of the advantage that Changchun has relatively lower temperature in the winter, the author implemented the experiment of fracture of ice layer exploration on the Nanhun Park of Changchun City, Jilin Province, China, and we obtained fracture of ice layer GPR profiles in three polarization modes-HH,VV and VH, then we made Pauli decomposition for GPR data of three polarization modes. Finally, we made explain for fractures in the ice layer by combining the results of GPR profiles and Pauli decomposition, and made classification by the roughness of the fractures.