基于探地雷达属性分析的隧道内溶洞三维可视化研究

3D visualization of karst caves in tunnels based on GPR attribute analysis

针对探地雷达法隧道内溶洞探测过程中存在位置标定模糊和形状确定困难等问题,提出了一种新的三维可视化方法。首先利用F-K偏移成像技术处理每条测线上的探地雷达数据,并根据坐标信息合成三维数据体,增强不同测线间的横向联系。然后通过属性分析提高探地雷达视图效果和有效反射数据的对比度,进而利用K-Means聚类方法提取溶洞反射数据的可视化振幅阈值参数。最后利用三维属性体和等值面提取技术实现隧道溶洞探地雷达三维可视化。模型试验和现场案例分析结果验证了本文方法的有效性,应用结果表明最大谱振幅属性不仅能够提高探地雷达视图效果,还能增强探地雷达数据体中有效反射数据的区分度,是本文方法较佳的输入属性。研究成果在一定程度上解决了探地雷达传统三维可视化方法振幅阈值设置时过度依赖解译人员经验问题,该方法适用于沉积岩层等层状介质解释。

The ground penetrating radar(GPR)can be used to detect and determine the scale,shape and position of hidden karst caves in tunnel construction,and it is very important for the protection of the tunnel construction safety and the hazard geology treatment.Due to the complexity of tunnel detection environment,the location calibration and the shape determination of the results for the traditional GPR 2D detection are difficult.However,due to the strong subjectivity of amplitude threshold setting,there is great uncertainty in the visualization process of GPR 3D data obtained based on the multiple survey lines.A 3D visualization method for the tunnel karst cave of GPR data is proposed.Firstly,to improve the imaging accuracy of karst cave targets,the F-K method is used to process each GPR B-scan.According to the coordinate information of GPR data,the GPR 3D data of the karst cave is synthesized to enhance the horizontal connection between different lines.Then,to improve the view effects and enhance the contrast of the effective reflection data,the method of GPR attribute analysis is used.The amplitude threshold of GPR 3D visualization of hidden karst cave is further extracted by using the K-means cluster method.Finally,the GPR 3D visualization of the tunnel karst cave can be realized by combining the attribute volume and the isosurface extraction technology.The reliability and adaptability of this method are verified by the model tests and field case analysis.The maximum spectral amplitude attribute is the optimal attribute of GPR signal in the proposed method,which may improve the radar view effect and enhance the contrast between the background and the effective reflection for GPR data.Furthermore,the proposed method solves the problem that the amplitude threshold setting of GPR 3D visualization excessively depends on the experience judgment of interpreters,and the results will be valuable for the stratigraphic analysis such as sedimentary strata.