Investigation On Characteristics Of Ground-Penetrating-Radar Antenna And Image Processing

Railway tunnel lining diseases (e.g. lining dehiscence, collapse, voids, etc.) are serious threats to traffic safety and normal operations, so inventing an effective means of detection is extremely urgent. Ground Penetrating Radar (GPR) technology is a non-destructive detection method that commonly used for railway tunnel lining disease detection. However, the method of using handheld GPR to detect the diseases during maintenance time cannot satisfy the considerable detection task for tunnel disease inspection and regular health check in a short period of time.In recent years, the railway departments are focusing on the research of vehicle-mounted GPR detection approaches for inspecting the railway tunnels in China. These methods have advantages of low cost, high efficiency, continuous detecting and multi-channel operation, and have shown great potential for tunnel disease detection. However, a problem arises in the application process that vehicle-mounted method needs air-coupled antenna to work at a certain distance from the surface of the lining. This process can be easily affected by the contact wires. In order to reduce the clutter effects, this thesis focuses on the research of the optimization of operation project and the method of model processing. The relevant main jobs are summarized as follows:Firstly, the measurement for half-power beam width of350MHZ air-coupled antenna in bistatic mode is proposed. Through the experiment, we got that half-power beam width of this antenna was68degree in the far-field. When the antenna beam center line is perpendicular to the ground, the detection range was approximately a circle and the maximum effective detection length of the antenna was equal to its distance from target.Secondly, the measurement to get the effects of contact wires under s simple hanging way with different antenna patterns and horizontal distance is proposed. Following conclusions were obtained by experiment:for the antenna moving perpendicular to the contact line, when the antenna is parallel with the contact line, the collected image of contact line and string hanging clamp is very vague, while perpendicular to the contact line, the image is very clear, and the string hanging clamp is presented in a form of hyperbola; for the antenna moving in a parallel direction along the contact line, the amplitude magnitude of the contact line and the string hanging clamp increases along with the reduction of the distance from the contact line to the antenna; Compared with the antenna perpendicular to the contact line, the parallel pattern has smaller proportion of contact line effects. When the distance between the antenna and the contact line is greater than75cm, the proportion is less than40%.Third, the target migration algorithm based on synthetic aperture and the hierarchical processing approaches are introduced. By processing the GPR detection data of tunnel lining, the results indicated that this approach not only weakened the influence of contact system effectively, but also the interested target signal in the deeper is retained well. And it is beneficial to objects interpretation. Furthermore, it is of great application value for processing measurement data collected by ground penetrating radar used air-coupled antenna at a long distace.