Application of GPR reverse time migration in tunnel lining cavity imaging

探地雷达逆时偏移在隧道衬砌空洞成像中的应用

Correctly locating the tunnel lining cavity is extremely important tunnel quality inspection.High-accuracy imaging results are hard to obtain because conventional one-way wave migration is greatly aff ected by lateral velocity change and inclination limitation and because the diff racted wave cannot be accurately returned to the real spatial position of the lining cavity.This paper presents a tunnel lining cavity imaging method based on the groundpenetrating radar(GPR)reverse-time migration(RTM)algorithm.The principle of GPR RTM is described in detail using the electromagnetic wave equation.The finite-difference timedomain method is employed to calculate the backward extrapolation electromagnetic fi elds,and the zero-time imaging condition based on the exploding-reflector concept is used to obtain the RTM results.On this basis,the GPR RTM program is compiled and applied to the simulated and observed GPR data of a typical tunnel lining cavity GPR model and a physical lining cavity model.Comparison of RTM and Kirchhoff migration results reveals that the RTM can better converge the diff racted waves of steel bar and cavity to their true position and have higher resolution and better suppress the eff ect of multiple interference and clutter scattering waves.In addition,comparison of RTM results of diff erent degrees of noise shows that RTM has strong anti-interference ability and can be used for the accurate interpretation of radar profi le in a strong interference environment.

隧道衬砌空洞的精确定位一直是隧道质量检测的难题之一。常规单程波偏移受横向速度变化和倾角限制影响较大,无法将绕射波精确归位到衬砌空洞的真实空间位置,成像精度不高。本文提出了一种基于探地雷达(GPR)逆时偏移的隧道衬砌空洞成像方法。首先从电磁波动方程出发,详细阐述了GPR逆时偏移原理,其中时域有限差分法(FDTD)用于计算反传电磁波场,基于爆炸反射面概念的零时刻成像条件用于获取逆时偏移结果。在此基础上,编制了相应的GPR逆时偏移程序,应用该程序对一典型隧道衬砌空洞模型的GPR正演数据和衬砌空洞物理模型的实测数据进行逆时偏移成像,并与克希霍夫偏移剖面进行对比。对比结果表明:逆时偏移能将钢筋网和空洞处的绕射波更好地收敛于真实位置,多次波和杂乱散射波压制效果更好,分辨率更高。此外,通过不同程度噪声的逆时偏移结果对比,表明逆时偏移具有较强地抗干扰能力,可用于强干扰等复杂环境下的雷达剖面精确解译。