Time-Frequency Analysis of Air-coupled GPR Data for Identification of Delamination between Pavement Layers

随着国家对交通基础设施的投入加大，全国高速公路的里程数日益增加，随之而来的道路工程问题也日益扩大，造成严重的社会影响和经济损失。探地雷达作为一种高性能的无损检测工具，不仅在工程勘探结果上直观准确，而且操作简便高效，在公路病害无损检测中已经得到广泛应用。然而，受限于探地雷达的工作带宽，在一些数值上需要精确测量的工程问题方面，探地雷达的分辨率仍然无法满足要求。 本文主要关注高速公路沥青面层与混凝土基层之间的剥离问题，利用时频分析工具对不同厚度薄层的雷达反射复合波频谱特性进行研究，从而提供一种道路层间剥离病害情况评估的参考依据。首先建立起沥青道路结构中间隙薄层的数值模型，利用分层介质格林函数（DG...With the mileage of the highway increasing, numbers of highway engineering issues arise, which causes serious damage to the social economy. Ground Penetrating Radar (GPR) is one kind of high performance non-destructive testing (NDT) technology. With its precise and efficient performance, GPR is comprehensively used in pavement inspection. However, limited by the bandwidth, the range resolution of ...学位：工程硕士院系专业：物理科学与技术学院_工程硕士(电子与通信工程)学号：3432014115280

Editorial of SI: GPR signal processing

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Development of GPR data analysis algorithms for predicting thin asphalt concrete overlay thickness and density

Thin asphalt concrete (AC) overlay is a commonly used asphalt pavement maintenance strategy. The thickness and density of thin AC overlay are important to achieving proper pavement performance, which can be evaluated using ground-penetrating radar (GPR). The traditional methods for predicting pavement thickness and density relies on the accurate determination of electromagnetic (EM) signal reflection amplitude and time delay. Due to the limitation of GPR antenna bandwidth, the range resolution of the GPR signal is insufficient for thin pavement layer evaluation. To this end, the objective of this study is to develop signal processing techniques to increase the resolution of GPR signals, such that they can be applied to thin AC overlay evaluation. First, the generic GPR forward 2-D imaging scheme is discussed. Then two linear inversion techniques are proposed, including migration and sparse reconstruction. Both algorithms were validated on GPR signals reflected from buried pipes using finite difference time domain (FDTD) simulation. Second, as a special case of the 2-D GPR imaging and linear inversion reconstruction, regularized deconvolution was applied to GPR signals reflected from thin AC overlays. Four types of regularization methods, including Tikhonov regularization and total variation regularization, were compared in terms of accuracy in estimating thin pavement layer thickness. The L-curve method was used to identify the appropriate regularization parameter. A subspace method—a multiple signal classification (MUSIC) algorithm—was then utilized to increase the resolution of 3-D GPR signals. An extended common midpoint (XCMP) method was used to find the dielectric constant and the thickness of the thin AC overlay at a full-scale test section. The results show that the MUSIC algorithm is an effective approach for increasing the 3-D GPR signal range resolution when the XCMP method is applied on thin AC overlay. Furthermore, a non-linear inversion technique is proposed based on gradient descent. The proposed non-linear optimization algorithm was applied on real GPR data reflected from thin AC overlay and the thickness and density prediction results are accurate. Finally, a “modified reference scan” approach was developed to eliminate the effect of AC pavement surface moisture on GPR signals, such that the density of thin AC overlay can be monitored in real time during compaction