THE DELINEATION OF THREE-DIMENSIONAL SHALLOW GEOMETRY OF ACTIVE FAULT BASED ON TLS AND GPR: A CASE STUDY OF AN NORMAL FAULT ON THE NORTH MARGIN OF MAOYABA BASIN IN LITANG,WESTERN SICHUAN PROVINCE

It is crucial to reveal the surface traces and activity of active faults by obtaining high-precision microtopography and three-dimensional shallow geometry. However, limited by the traditional geological investigation methods in the field and geological condition factors, the measurement method on microtopography and shallow geometry of active fault is badly insufficient. In this study, the TLS and GPR are firstly used comprehensively to delineate the microtopography and shallow geometry of the normal fault scarp on the north margin of Maoyaba Basin in Litang. Firstly, the vertical displacements of two landforms produced by the latest two periods of normal faulting and the two-dimensional GPR profiles are obtained separately. Secondly, the three-dimensional measurement method of active fault based on TLS and GPR is preliminarily established. On this basis, three-dimensional model of fault scarp and three-dimensional images of subsurface geometry are also obtained. These data all reveal a graben structure at normal fault scarps. Thirdly, the fusion and interpretation of three-dimensional data from the surface and subsurface are realized. The study results show:1)the vertical displacements of the T₁ and T₂ terraces by the normal fault movement is 1.4m and 5.7m, the GPR profile shows a typical fault structure and indicates the existence of small graben structure with a maximum width of about 40m in the shallow layer, which further proves that it is a normal fault. 2)the shallow geometry of the normal fault scarp can be more graphically displayed by the three-dimensional radar images, and it also makes the geometry structure of the fault more comprehensive. The precise location and strike of faults F₁ and F₂ on the horizontal surface are also determined in the three-dimensional radar images, which further proves the existence of small graben structure, indicating the extensional deformation characteristics in the subsurface of the fault scarps. Furthermore, the distribution of small graben structure on the surface and subsurface is defined more precisely. 3)the integrated display of microgeomorphology and shallow geometry of normal fault scarp is realized based on the three-dimensional point cloud and GPR data. The fusion of the point cloud and GPR data has obvious advantages, for the spatial structure, morphological and spectral features from the point cloud can improve the recognition and interpretation accuracy of GPR images. The interpreted results of the GPR profiles could minimize the transformation of the surface topography by the external environment at the most extent, restore the original geomorphology, relocate the position and trend of faults on the surface and constrain the width of deformation zones under the surface, the geological structure, and the fault dislocation, etc. In a word, the TLS and GPR can quickly and efficiently provide the spatial data with multi-level and multi-visual for non-destructive inspection of the microgeomorphology and shallow structure for the active fault in a wide range, and for the detection of active fault in the complex geological environments, and it is helpful to improve the accuracy and understanding of the investigation and research on microtopography and shallow geometry of active faults. What's more, it also offers important data and method for more comprehensive identification and understanding of the distribution, deformation features, the behaviors of active faults and multi-period paleoseismicity. Therefore, to continuously explore and improve this method will significantly enhance and expand the practicability and application prospects of the method in the quantitative and elaborate studies of active faults.     

基于MED的探地雷达信号处理研究

   文中运用改进的最小熵反褶积（MED） 理论,采用MATLAB编写程序,实现了改进的MED计算机自动处理功能。将 其应用到在建中的某地铁4号线某区间的探地雷达资料处理中,较准确地确定了岩溶的位置和尺寸。将处理结果与钻孔岩 芯资料进行比照,发现雷达探测结果与钻探结果具有较好的一致性,表明MED方法能在雷达剖面上有效显示溶洞位置,该 项研究成果对类似工程具有重要借鉴意义。     

闪电起始过程时空特征的宽带干涉仪三维观测

闪电的起始位置和起始阶段发展速度是闪电研究中的重要问题。2010年夏季,使用架设在广州市从化区的两套甚高频 (VHF) 宽带干涉仪对闪电的起始阶段放电过程进行三维定位观测。对观测数据给出的地闪和云闪的起始高度分布特征以及起始阶段击穿过程的时空发展特征进行统计和对比分析,结果表明:闪电的起始高度分布呈双峰值特征,分别在5.0 km和8.8 km有两个明显的分布峰值,符合雷暴云三极性总体电荷结构的描述。对起始阶段闪电放电发展速度的计算表明,云闪和地闪在起始阶段的前15 ms内的平均发展速度均在104~105 m·s-1量级之间;多数云闪、地闪起始阶段前15 ms内的平均发展速度表现出减速趋势,但云闪个例中起始阶段前10 ms存在减速趋势的比例更高,且其中在前15 ms一直保持减速趋势个例所占比例也大于地闪。云闪和地闪的起始阶段放电过程的发展方向有向上、向下和水平发展3种情形,可用于指示闪电始发位置的环境电场方向。     

一种小型化双低频4T4R基站天线阵列设计方法

能够支持双低频4T4R的MIMO基站阵列天线已成为目前运营商布网主流,当采用常规设计时,往往造成天线尺寸过大、风载荷过高等问题.在MIMO阵列天线小型化设计时,由于各阵列间距离缩小,电磁耦合急剧上升,导致各天线水平面波束宽度恶化,性能下降严重.针对此问题,提出了一种小型化阵列天线设计方法.采用波束合成技术,利用一种功率比随频率变化的新型不等功分电桥复用一组辐射单元,这样每列天线均可复用一个窄波束宽度单元,再通过该窄波束单元与其他宽波束单元合成理想的水平面波束宽度,提升天线覆盖性能.实测结果表明：采用本文阵列天线设计方法能够得到收敛的水平面波束宽度,范围在56°~68°,同时具有较好的增益和系统隔离度,大幅改善了天线性能.     

全极化探地雷达正演模拟

全极化探地雷达不但能获取当前探地雷达使用的共极化信息,而且能使用交叉极化信息,进而更好地分析目标属性.本文在时域有限差分法的基础上,构建了全极化探地雷达的正演模拟方法,通过水平正交双方向同时接收获取全极化信息.标准目标体金属板和角反射器的正演模拟与实验室物理模型测试一致的共极化和交叉极化响应信息,证实了该正演模拟方法的有效性.同时还模拟了典型目标(随机表面和斜裂缝)的响应.正演模拟和实验结果均反映出结合交叉极化响应和共极化响应信息有助于识别和判断目标的方向、结构组成等属性.     

利用宽频带倾斜仪观测资料检测日本9．0级大地震激发的地球自由振荡

本文利用张家口台宽频带倾斜仪的数字化观测资料,采用功率谱密度估计方法,在没有对资料进行去固体潮处理的情况下,准确获得了2011年3月11日日本9．0级大地震激发的oS2～oS35,基频球型自由振荡,并与地球初步参考模型（PREM）的理论自由振荡频率进行了对比,发现实测振荡频率与PREM预测的振荡频率基本符合。宽频带倾斜仪的数字化观测资料的确可以提取到日本地震激发的地球自由振荡。     

Soil properties and performance of landmine detection by metal detector and ground-penetrating radar — Soil characterisation and its verification by a field test

Metal detectors have commonly been used for landmine detection, and ground-penetrating radar (GPR) is about to be deployed for this purpose. These devices are influenced by the magnetic and electric properties of soil, since both employ electromagnetic techniques. Various soil properties and their spatial distributions were measured and determined with geophysical methods in four soil types where a test of metal detectors and GPR systems took place. By analysing the soil properties, these four soils were classified based on the expected influence of each detection technique and predicted soil difficulty. This classification was compared to the detection performance of the detectors and a clear correlation between the predicted soil difficulty and performance was observed. The detection performance of the metal detector and target identification performance of the GPR systems degraded in soils that were expected to be problematic. Therefore, this study demonstrated that the metal detector and GPR performance for landmine detection can be assessed qualitatively by geophysical analyses.     

The role of GPR techniques in determining ice cave properties: Peña Castil ice cave,Picos de Europa

The structure and ice content of ice caves are poorly understood. Ground penetrating radar (GPR) can provide useful insights but has only rarely been applied to ice caves. This paper interprets GPR images (radargrams) in terms of internal structure, stratification, compaction, thickness and volume of the ice block in the Peña Castil ice cave (Central Massif of Picos de Europa, northern Spain), providing the endokarst geometry of the ice cave in GPR data reflections. Eight radargrams were obtained by applying a shielded ground‐coupled antenna with a nominal frequency of 400 MHz. Although the radargrams do not depict the ice–basal bedrock interface, they suggest that the ice block is at least 54 m deep and similarly thick. Some curved reflection signatures suggest a potential vertical displacement in the block of ice, and thus certain dynamics in the ice body. Other images show numerous interbedded clasts and thin sediment layers imaged as banded reflections. In this particular cave a direct visual inspection of the ice stratigraphy is a difficult task but GPR provides clear reflectivity patterns of some of its internal features, making GPR a suitable instrument for this and future studies to achieve a better and broader understanding of the internal behavior of ice caves.     

基于变换光学有限差分探地雷达数值模拟研究

在采用有限差分方法开展探地雷达复杂目标体精细结构模拟时,为了提高计算精度,常采用非均匀网格对目标区域划分小尺寸的网格,以压制离散网格频散现象和保证有限差分方法的稳定性.常规非均匀网格和自适应亚网格技术在网格剖分数量和粗细网格边界处理上难以达到计算效率和计算精度的均衡.本文根据隐形斗篷(invisible cloak)理论,将基于变换光学(Transformation optics)理论应用于有限差分探地雷达数值计算中.该理论的主要思想是基于目标参数变化而保持电磁场的传播不变性,在坐标变换后,Maxwell方程的形式可以维持不变,而使得相对介电常数与磁导率的表达式变得复杂.通过这种方式可以虚拟地扩大目标体所占的网格节点数,减少背景介质区域的网格数,不增加模型空间的网格总数.另外,这种网格划分方式不但提高了计算效率,同时也可以克服亚网格技术边界反射误差的影响.本文推导实现了基于变换光学的二维有限差分方法,通过典型探地雷达模型测试,对比分析了该方法与常规有限差分、变网格有限差分和自适应亚网格有限差分的优缺点.计算结果验证了基于变换光学的有限差分可用于探地雷达目标精细结构模拟,具有较高的计算精度和计算效率.     

时域有限差分法(FDTD)模拟探地雷达极化测量

由于探地雷达偶极天线具有电磁极化特性,其发射天线主要发射沿着天线长轴方向的线性极化波,而接收天线对这种极化方向的电磁波也最灵敏。因此,在对混凝土中钢筋、电缆等目标体进行检测时,利用天线的极化特性可以了解目标体的延伸。时域有限差分法是麦克斯韦方程的直接时域法,其计算简单、直观、灵活性强、计算精度高、动态范围大。利用时域有限差分法(FDTD)对地质雷达极化测量进行了正演模拟,取得了很好的效果。