非均匀介质的探地雷达全波形反演研究

Ground Penetrating Radar has been widely used in the near-surface exploration. Due to the approximation empolyed by the classic data processing approaches, including the homogeneous medium model and Born approximation, they are not applicable for the subsurface detection with heterogeneous environment. This project trys to introduce the Full-waveform Inversion (FWI) approach into the inversion of heterogeneous medium. The research is based on the exact simulation of the electromagnetic wave and distribution modeling the heterogeneous medium. First the antenna model of GPR would be constructed using electromagnetic simulation that can explain the near field propagation of electromagnetic wave radiated by the GPR antenna. A database that involving models of different GPR antennas is planned. Next, the exact characterization of subsurface heterogeneous medium would be achieved by a medium model with distributed electromagnetic parameters, relying on which the behavior of electromagnetic wave in heterogeneous medium would be investigated. In this step, we are focusing on finding the spreading law between the medium parameters and the electromagnetic responding, based on which the gradient propagation manner from the fitting error to the medium parameters would be derived. With the gradient propagation manner, we would fix the current model optimization algorithm, making it suitable to the FWI of homogeneous medium from GPR data. At last, the parallel computation technologies would be introduced in the FWI structure, and finally achieving the effective exploration of the near-surface space.

探地雷达广泛应用于浅表层地下空间的探测。由于传统处理手段对介质采用均匀假设，对电磁波传播基于玻恩近似，对介电属性起伏较大的非均匀介质的GPR探测带来较大误差，不能满足对浅表层地下空间精确探测的需求。本项目针对非均匀介质的探地雷达探测应用场景，研究基于精确电磁计算和分布式参数模型表征的全波形反演算法。首先基于电磁计算和仿真手段建立探地雷达天线的近场精确电磁模型，构建模型库。然后构建非均匀介质的分布式参数模型表征，研究电磁波在非均匀介质中的传播特性；揭示探地雷达接收波场对模型参数变化的响应规律，推导模型参数误差的传导机制，进而获取模型优化的梯度传导机制，完善全波形反演的模型优化算法。研究引入全并行计算技术，提升全波形反演计算效率，构建非均匀介质的探地雷达准确高效全波形反演体系，实现对浅表层地下空间的探测高精度探测。

探地雷达是探索浅层地下空间的有效物探工具，在矿产勘查、灾害地质调查、岩土工程勘察、工程质量检测、建筑结构检测以及军事目标探测等众多领域的应用日益广泛。近些年来，在安防检查、生物医学、太空探测等领域，也有了不少研究成果应用，发展前景广阔。由于传统成像处理手段对介质采用均匀或分层均匀假设，对电磁波传播基于玻恩近似，对介电属性起伏较大的非均匀介质的GPR探测带来较大误差，不能满足对浅表层地下空间精确探测的需求。为解决GPR探测介质未知的难题，本项目研究基于精确电磁计算和分布式参数模型表征的全波形反演算法。项目达到了预期研究目标，针对针对基于（分层）均匀假设、远场分析手段和波恩近似的GPR数据处理方法导致误差较大，无法精确、定量获取信息的问题，基于数值电磁计算方法研究电磁波与非均匀介质的复杂相互作用，研究了基于L-BFGS双循环递归的表层探测模式下的GPR全波反演，实现了GPR表层探测条件下分布式建模与反演方法；针对表层GPR全波反演的强非线性导致易陷入局部最优解的问题，提出频率多尺度反演及优化频带选择方法，并分析了不同频带下的反演结果；针对表层GPR反演的不适定性问题，提出了双边全变差约束的全波反演方法，保留了反演结果的边缘信息且抑制了反演结果背景的非物理振荡，提高了反演精度；瞄准解决介质内部体层析、天体次表层探测等问题，研究了环绕扫描模式下的全波反演方法，实现了对介质内部地层结构的空间重构。此外，项目研制了一套高精度的任意路径扫描实验平台，为开展全波反演内场实验打下基础，并针对实测数据表层杂波对反演的干扰问题提出了自适应SVD杂波抑制方法。项目引入了全并行计算技术，提升了全波形反演计算效率，构建非均匀介质的探地雷达准确高效全波形反演体系，实现对地下目标和介质的精确定量分析，延伸人类对地下探测的视界