基于背景矩阵减法的探地雷达杂波信号抑制方法研究

探地雷达是探测浅层地下目标并对其空间分布进行成像的重要地球物理方法之一,但在实测雷达剖面中,目标反射信号不可避免地会受到直达波和地面反射波等杂波信号的干扰。为了提高探地雷达数据解译的可靠性和准确性,需要对杂波进行抑制或去除。提出一种背景矩阵减法来抑制杂波信号,并通过两组仿真数据和两组实测数据示例与减平均道法、奇异分解法对杂波抑制效果进行对比分析,结果表明背景矩阵减法的效果明显优于减平均道法和奇异分解法,可以在保证有效信号不丢失,幅值和相位不失真的基础上,使杂波得到较好地抑制,有助于识别探地雷达剖面中目标信号的特征,提高数据解译准确性和可靠性。     

三维地质雷达探测技术在城市道路空洞病害普查中的应用研究

由城市道路地下空洞、路面脱空、土体疏松等病害引起的道路塌陷事故是目前国内许多城市面临的重大安全隐患。城市道路空洞病害具有隐伏性、突发性,造成的灾难性后果长期以来困扰着城市安全运营。以国内多地的项目实测及验证成果为基础,对三维地质雷达探测技术方法和工作流程进行了梳理,通过分析三维地质雷达剖面数据中病害体的顶界面反射、多次波反射、边界绕射波等异常特征和三维地质雷达切片数据中病害体周边地下管、井分布特征,总结了三维地质雷达技术在城市道路地下脱空、空洞病害探测中病害体的数据异常特征。实践研究证明,三维地质雷达探测技术以其作业高效、定位精准、抗干扰能力强、数据丰富全面等优点可有效地探测出道路下方存在的空洞等安全隐患,为城市道路病害的防患和治理提供准确、可靠的依据。     

基于Curvelet变换的隧道裂隙水GPR数据处理研究

应用地质雷达探测隧道内部裂隙水的分布状况时,受隧道钢筋网的影响以及噪声干扰,导致探测信号中弱有效信号难以识别。Curvelet变换可以对二维信号从频率、角度和空间位置实现有效反射波和干扰波的分离及降噪处理,应用Curvelet变换对含钢筋网干扰的裂隙水模型的探地雷达模拟数据进行波场分离和降噪处理,在压制直达波、去除钢筋层反射信号及多次反射的基础上,可以有效地提取出含裂隙水所引起的反射波信号。将该方法应用到汝郴高速某隧道实测探地雷达数据中,较好地去除了钢筋层反射信号的影响,准确地判断出了裂隙水的空间分布位置,证明了所提出方法的有效性。     

地质雷达探测技术在地基空洞探测中的应用

在房山区大董村拟建工程基坑开挖和CFG桩施工过程中,发现地层中存在空洞。为确保天然地基的安全,首先选定重点区域采用地质雷达探测异常区,然后采用钻探开挖手段进行确认。根据工地的地质情况,在选定的重点区域采用井字形与往返方式布设雷达测线34条。为准确了解雷达波对地下空洞的相应特征,按照与实际尺寸1∶20建立地下空洞模型,并运用Gprmax软件进行正演模拟,通过与现场实测剖面对比分析发现,空洞可造成雷达反射波同相轴不连续,且其波形呈现典型的双曲线形态。利用地下空洞在雷达剖面上响应特征,确定了工区内选定区域的空洞位置、大小及埋深,经开挖验证,解译结果可靠。根据解译结果绘制的场地内空洞异常分布图,为基础开挖、塔吊和桩基安全施工提供了依据。     

探地雷达剖面的相干加强处理

简述了用相干分析法对探地雷达反射剖面进行处理的方法原理,并结合雷达剖面的特征编制了雷达记录道相干加强处理的实用程序。对实测雷达剖面进行处理的结果表明:雷达记录道相干加强处理能有效改善来自同一界面的雷达反射波同相轴的连续性,有利于反射界面的追踪,同时不会引起同相轴的形态发生畸变。     

反射波法对嵌岩桩的检测特征及异常分析

通过实例，分析了用反射波法测试不同嵌岩桩的桩端反射波特征。完好嵌岩桩的波表曲线具有明显的桩底信号，在入射波与桩底反射波之间没有什么异常；而当桩身有缺陷，持力层软弱或者存在夹层时，桩底信号相位与入射波相位相同。通过进一步分析，钻心查证，即可判断桩身，软弱层，夹层以及桩端及桩端与持力层的接触情况等。     

路基病害的探地雷达正演模拟与探测

探地雷达勘探是一种分辨率比较高的工程地球物理方法,对道路路基中存在的局部脱空、不密实和含水丰富等病害有明显的异常反应。这里介绍了地质雷达在路基中的探测原理,在分析不良地质现象与围岩之间的结构和介电性差异特征的基础上,设计了较为合理的正演模型,通过GPRMax2D软件进行正演模拟,分析正演模拟图像的波形、频率、振幅、相位等特征,总结了路基病害在雷达图像上的信号特征,并通过对实测雷达图像的解译,对道路病害的雷达反射波的频谱特征做了进一步研究,可为道路路基病害探测的地质雷达数据解译提供参考。     

点状不良地质体钻孔雷达响应特征 ——围岩及充填效应正演分析

钻孔地质雷达探测是一种有效获取高分辨率深部岩体信息的井中地球物理方法。针对钻孔地质雷达探测工作中常见的空洞、岩溶和地下埋藏物等点状不良地质体,利用时域有限差分数值模拟方法,对岩土体内点状不良地质体围岩介质和充填状况进行了雷达响应正演研究,分析了这些点状不良地质体围岩介质和充填状况对钻孔地质雷达反射信号的影响。研究结果表明,围岩与空洞内充填物的相对介电常数相对值,决定着雷达反射剖面信号的强弱对比,介电常数相对值较大时,更易确定目标地质体的前、后部界面位置,而低阻围岩的雷达波信号大部分被围岩介质吸收,通过单孔反射方法几乎不可能探测到空洞的存在。通过反射信号强度和正负相反射特性及其强弱变化,可以定性地判断空洞内填充物质的性质。     

井间地震弹性波传播特征数值模拟

采用弹性波方程数值模拟和Zoeppritz方程解相结合的方式,研究了井间地震固-固界面上以及低速和高速夹层中弹性波场特征及传播规律.给出了井间地震弹性波的主要类型,其中包含一种特殊面波,该面波由激发井和接收井内的地层界面处产生的二次源形成,并说明了反射波以广角反射占优势;利用正演模拟记录对广角反射现象进行了分析,得出了在临界角处广角反射波的振幅、相位突变,极性反转,这与反射系数变为复数相对应;提出利用临界反射波特征和临界反射点位置来确定地层速度.震源在高速夹层中激发时,其中传播的弹性波场简单;而在低速夹层中,则弹性波场非常复杂.低速夹层中的导波存在明显的频散现象,其振幅和频率与低速层的速度和厚度密切相关.提出利用导波可以确定低速层的横向变化和连通性.     

矿井地质雷达超前探测正演模拟

用时间域有限差分(FDTD)法建立矿井地质雷达的模型。采用理想频散关系和超吸收边界条件,对几个典型矿井地电模型进行了正演模拟,研究了矿井地质雷达超前探测的剖面特征。巷道对各道直达波能量分布及波列形状有明显影响;煤岩分界面主要影响反射波能量分布。      

桩底溶洞探测中瞬时相位差强度计算方法的优化及应用

双通道桩底溶洞声呐探测方法是岩溶地区钻孔灌注桩特殊泥浆施工环境下一种有效的溶洞探测方法,其中所运用的瞬时相位差强度(IPDI)分析方法可以用于提取溶洞顶底板的微弱反射信号并揭示溶洞位置。但该溶洞探测方法中一些关键参数的取值对溶洞探测效果的影响规律不明确,可能导致计算所得溶洞顶底板位置及溶洞大小的精度发生损失。本文旨在得到IPDI计算中关键影响因素及其影响规律从而达到优化效果,并将其运用于模拟工况以及实测信号的IPDI分析验证其有效性。首先,采用二维黏弹性波方程和交叉网格时域有限差分建立了溶洞探测仿真数值模型。接着将其用于探索IPDI计算过程中采样率、总体平均经验模态分解(EEMD)中总体平均次数、标准差等关键参数的影响规律并进行优化,尝试运用灰色预测模型抑制探测结果的端点效应。最后,将优化方法运用于工程实测信号IPDI分析过程。结果表明,当采用0.5~1MHz的采样率,并在EEMD过程中选取0.1作为标准差以及300~600作为总体平均次数能够使溶洞顶底板位置和溶洞大小的探测精度得到提升。当采用灰色预测模型抑制IPDI图像端点效应时,能够有效减缓其两端的异常“飞逸”现象。在进行实测信号优化分析时,发现针对实测信号的零漂现象采用将重构信号减去EEMD过程所得到的趋势项的优化方法,能够得到原先被掩盖的溶洞底板反射信号并计算出溶洞底板位置,并且经与钻孔柱状图对比,其计算结果准确可靠。相较任意选取参数时的探测结果,本文提出的优化方法的确能够帮助提升双通道溶洞声呐探测方法的精确度。     

隧道衬砌空洞探地雷达图谱正演模拟研究

探地雷达作为一种高效、先进的无损检测设备,能够对隧道衬砌实施连续扫描,实时获得雷达图谱。然而,由于探地雷达在我国的应用时间还非常短暂以及雷达图谱的复杂性,隧道衬砌空洞探地雷达图谱的辨识还存在一定的问题。据此,通过不同环境的试验得到空洞雷达图谱特征,并利用二维时域有限差分法对衬砌空洞雷达图谱进行正演模拟。采用VC++语言编写探地雷达正演模拟程序,对隧道衬砌检测中常见的几种空洞模型进行正演模拟,得出模拟波形和图谱,并与实测隧道衬砌空洞的探地雷达波形和图谱进行对比。结果表明,模拟图谱与实测结果相似,具有较明显的空洞特征。良好的结果也验证了二维时域有限差分法（2D-FDTD）正演模拟的可行性。     

金属矿地震绕射波分离与成像——以庐枞矿集区和钦杭成矿带为例

不同于油气藏能源大多产于沉积地层之中, 金属矿成矿部位的地质条件要更为复杂多变。通常情况下矿体表现为不规则形状, 且连续性较差, 难以满足现有地震反射波法所以依据的镜面反射条件(徐明才等, 2009)。不同的围岩地震地质条件差异很大, 甚至同一种岩性受到蚀变、构造作用的影响, 表现出不同的阻抗特征, 当围岩与矿体间的波阻抗差异较小, 难以形成有效的反射波。在控矿构造方面, 通常大规模的构造对成矿具有控矿、控岩作用, 而与成矿部位密切相关的一般是小规模的断裂, 反射波较难识别。根据菲涅耳带理论, 当地质体的尺度小于地震波的一个波长时, 反射地震成像精度会骤降, 而来自这些小尺度、非均匀地质体产生的绕射波和散射波成像较反射波成像具有明显的高分辨率、甚至超高分辨率。利用绕射波成像能够探测和识别地下重要的构造信息, 如破碎带、断层、尖灭点、礁体边界、次火山岩、小尺度的侵入体、不规则盐丘体, 以及其他不连续的地质体(Karimpoul et al., 2015)。考虑金属矿围岩及控矿构造复杂, 矿体几何尺寸较小、形状不规则, 容易产生绕射波, 理论上利用地震绕射波识别这些地质体较反射波更具优势。     

The Influence of Conductivity on the Reflected Ground Penetrating Radar SIgnal Amplitude

Within the ground-penetrating radar (GPR) bandwidth a subsurface materials is considered to be an ideal dielectric, which is not always the case. We have developed the dependence of the reflection coefficient of electromagnetic waves with regard to conductivity, which showed a significant effect of the difference in conductivity on the reflectivity and signal amplitude. This was confirmed by physical modeling. The electrical conductivities of a geological media should be taken into account when solving direct and inverse problems, survey design planning, etc. Ground-penetrating radar can be used to solve the problem of mapping of the halocline or to determine water contamination.     

The outer scale of solar-wind turbulence from GALILEO coronal-sounding data

Radio sounding experiments on of the solar plasma were carried out by the GALILEO spacecraft using S-band (2295 MHz) signals in 1995–1996 a period of minimum solar activity. Equatorial regions at heliocentric distances of 7–80 solar radii were studied. The frequency of the received signal was detected by three ground stations. By carrying out continuous observations of unprecedented duration and processing the data using spectral and correlation methods, we have obtained reliable information on large-scale inhomogeneities of the solar-wind density for the first time. The outer turbulence scale increases with heliocentric distance, the dependence being close to linear. We estimate the outer turbulence scale and analyze its dependence on distance from the Sun and local plasma parameters for a model in which the outer scale is formed due to competition between the linear amplification of Alfven waves in the irregular, moving solar-wind plasma and the nonlinear transfer of turbulent energy to higher frequencies. A comparison of predictions for various specific cases of this model with the observational data suggests that the main nonlinear processes responsible for the formation of the inertial range of the spectrum on the investigated scales are three-wave decay processes involving Alfven and magnetoacoustic waves.     

地下深部灰岩岩石特性的单孔雷达反射研究

灰岩中岩溶和裂隙发育规律研究是研究陷落柱发育规律的基础,研究结果表明在单孔雷达反射图像上岩溶和裂隙反映清晰,单孔雷达反射法用于灰岩岩石特性研究效果显著,该研究成果填补了国内灰岩岩石特性的单孔雷达反射研究的空白,为地下深处灰岩岩石特性高分辨率探测开辟了新途径。     

Radar spectral analysis and evaluation of the effect of grouting treatment in karst caves and soil caves

This paper studies karst cave and soil cavity development in the process of karst collapse as a means of disaster prevention and control. Using the karst area of the Shandong section of the Beijing–Shanghai high-speed railway as a test area, a numerical simulation method is presented as well as the model test to study the characteristics of typical radar images of different types of karst caves and soil cavities. By combining theoretical analysis with field test results, the method and characteristic standards for nondestructive testing using ground-penetrating radar to determine the grouting effect on a karst roadbed are given. The radar spectrum characteristics are analyzed for a cave, water-filled cave, clay-filled cave, karst cave with dense grouting and karst cave with grouting that is not dense. Comprehensive analysis of the results of indoor model testing and numerical analysis, combined with the engineering practice of evaluating the effect of grouting treatment in the selected section of the Beijing–Shanghai high-speed railway, clarifies the basic characteristics of map recognition of radar detection of karst grouting. The morphological characteristics of the karst caves in the geological radar images are usually composed of many hyperbolic strong reflection waves. Multiple-reflection wave groups of high amplitude, low frequency, and equal distance indicate the side wall of the cave. The bottom interface of the cave is not obvious, although when the bottom part of the cave is filled with water or clay, silt, sand and gravel material. The bottom of the reflection wave will be enhanced. When the cave is filled with material, the electromagnetic wave energy decays rapidly, the high-frequency part is absorbed, and the reflection is mostly low frequency wave. The characteristics of radar images of the slurry distribution area are obvious in the grouting zone. A horizontal direction results in arc-shaped distribution, and a vertical direction has more regular distribution. The results of the study are helpful in the exploration of karst caves and soil caves, and the evaluation of the effect of grouting treatment in mitigating karst collapse.     

Application of high resolution seismic reflection techniques for fracture mapping in crystalline rocks

Surface reflection seismic techniques have the capability of mapping subsurface geological features without disturbing the rock mass. They also have an added capability of penetrating to a much deeper depth than any other geophysical technique, including the ground probing radar. However, the successful application of reflection seismic techniques in crystalline rocks has in general been more difficult than in sedimentary basins, because of the irregular geometry and low acoustic impedance contrasts across geological boundaries. In this paper, we describe the imaging of fracture zones in crystalline rocks. Effective data processing, carefully modified from the conventional approaches, was applied on two high-resolution field data previously collected by different contractors. The strategy included enhancement of the signal hidden under the large-amplitude scattering noise, through pre- and post-stack processing such as shot f-k filtering, residual statics and careful muting after NMO correction. Two sets of low S/N test data from Canada and Sweden are analyzed in this research. The reflected energy in these data sets appeared to be more closely related to fracturing than to lithologic boundaries. The major fracture zones at shallow depth have been mapped with the desired resolution and can be correlated to the available well-log and seismic crosshole tomographic data. Once the surface waves were removed, shallow reflectors in the fracture zones could be identified and analyzed on the field records. Focusing analysis of the seismic image was performed in the constant-offset section to investigate the trends of major fracture zones. The complex attributes were also analyzed to determine whether they could be applied to the shallow fracture zones. Instantaneous frequency plots outline the intense fracturing zone and instantaneous phase plots identify the major and minor fractures, and other coherent events with different dip attitudes which interfere with each other.