College of Geo-Exploration Science and Technology, Jilin University, Changchun 130026, China.
State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China.
Sensors (Basel). 2018 Sep 15;18(9):3114. doi: 10.3390/s18093114.
Xiuyan Jade, produced in Xiuyan County, Liaoning Province, China is one of the four famous jade in China. King Jade, which is deemed the largest jade body of the world, was broken out from a hill. The local government planned to build a tourism site based on the jade culture there. The purpose of the investigation was to evaluate the stability of subsurface foundation, and the possible positions of mined-out zones to prevent the further rolling of the jade body. Cross-hole radar tomography is the key technique in the investigation. Conventional travel time and attenuation tomography based on ray tracing theory cannot provide high-resolution images because only a fraction of the measured information is used in the inversion. Full-waveform inversion (FWI) can provide high-resolution permittivity and conductivity images because it utilizes all the information provided by the radar signals. We deduce the gradient expression of the time-domain FWI with respect to the permittivity and conductivity using a method that is different from that of the previous work and realize the FWI algorithm that can simultaneously update the permittivity and conductivity by using the conjugate gradient method. Inverted results from synthetic data show that time-domain FWI can significantly improve the resolution compared with the ray-based tomogram methods. FWI can distinguish targets that are as small as one-half to one-third wavelength and the inverted physical values are closer to the real ones than those provided by the ray tracing method. We use the FWI algorithm to the field data measured at Xiuyan jade mine. Both the inverted permittivity and conductivity can comparably delineate four mined-out zones, which exhibit low-permittivity and low-conductivity characteristics. Furthermore, the locations of the interpreted mined-out zones are in good agreement with the existing mining channels recorded by geological data.
岫岩玉，产自中国辽宁省岫岩县，是中国四大名玉之一。产自一座小山的玉石王，被认为是世界上最大的玉石体。当地政府计划以当地的玉石文化为基础，打造一个旅游景点。本次调查的目的是评估地下基础的稳定性，以及采空区的可能位置，以防止玉石体进一步滚动。井间雷达层析成像技术是调查的关键技术。基于射线追踪理论的常规走时和衰减层析成像不能提供高分辨率图像，因为反演中只使用了测量信息的一部分。全波形反演 (FWI) 可以提供高分辨率的介电常数和电导率图像，因为它利用了雷达信号提供的所有信息。我们使用与以前工作不同的方法推导出时域 FWI 对介电常数和电导率的梯度表达式，并通过共轭梯度法实现了可以同时更新介电常数和电导率的 FWI 算法。合成数据的反演结果表明，与基于射线的层析成像方法相比，时域 FWI 可以显著提高分辨率。FWI 可以区分小至半波长到三分之一波长的目标，并且反演的物理值比射线追踪方法提供的更接近真实值。我们将 FWI 算法应用于在岫岩玉矿测量的野外数据。反演得到的介电常数和电导率都可以很好地描绘四个采空区，这些采空区表现出低介电常数和低电导率的特征。此外，解释的采空区的位置与地质数据记录的现有开采通道非常吻合。
