地下水污染调查中探地雷达有限差分数值模拟

基于探地雷达正演模拟软件GprMax,针对地下水不同污染途径和不同污染介质,建立了地下水污染的5种模型,采用有限差分法进行了数值模拟计算。模拟结果表明探地雷达在探测地下水污染中有较好的应用效果。     

注浆材料介电常数在雷达图像识别中的应用

利用探地雷达(GPR)方法探测软土盾构隧道盾尾壁后注浆分布效果时,电磁波在介质中的传播速度是准确识别介质界面的关键。在估计波速时常常将介质的介电常数假设为固定不变的常数,这不符合实际情况。为保证探测图像识别的精度,首次利用网络分析仪对不同配比、不同探测频率和不同龄期下软土隧道壁后注浆材料的介电常数进行了测定,对测定结果进行了基于射线追踪原理的GPR数据二维正演分析,并将分析结果与模拟的探地雷达隧道壁后注浆分布探测结果进行了比较。结果表明,针对不同的探地雷达探测频率而采用相应的介质介电常数来进行探地雷达探测图像的准确识别是十分必要的。     

有耗介质探地雷达波传播衰减特性的研究

探地雷达是利用超高频脉冲电磁波探测地下介质分布的一种浅层地球物理勘探方法,探地雷达超高频、宽频带脉冲电磁波在地下有耗介质中的衰减特性是一个十分复杂的过程。本文从电磁波传播的麦克斯韦方程出发,较为系统地研究和分析了雷达脉冲电磁波在有耗介质中传播的衰减特性,对研究雷达脉冲电磁波在地下有耗介质中的传播机制有指导意义。     

探地雷达技术在公路病害探测中的应用

探地雷达是一种基于介质电磁性质差异的非破坏性测试技术,具有快速、简捷、抗干扰能力强、分辨率高等优点。公路路面、基层、路基和地基等结构层之间存在电磁性质差异,且路基病害造成的结构破坏导致各种介质相互混合,也使得病害区段介质电磁性质与周围明显不同。因此,公路病害的雷达探测具备基本物理前提。以某高速公路裂缝等病害探测为实例,阐述了探地雷达原理和工作方法技术及其在裂缝发展程度、路基不密实区、是否存在空洞等病害特征及其成因探测中的有效性。     

地下人防巷道上方探地雷达异常特征与实际应用

探地雷达是利用宽带高频电磁波以脉冲形式来探测地表之下介质内部结构分布规律的一种地球物理方法。它广泛用于灾害地质勘查、浅地表地下隐蔽物探测和工程质量检测等众多领域。本文用正演方法给出不同情形下的地下人防巷道上方探地雷达异常特征,并据此进行了实际应用。提出了利用探地雷达法进行地下人防巷道探测时,在异常识别方面应注意的问题。     

低频探地雷达探测冻土带天然气水合物正演模拟研究

通过对低频探地雷达在青藏高原冻土带环境下的探测深度、分辨率及反射特征分析的正演模拟来研究其在冻土带天然气水合物勘探中的可行性和关键参数。首先通过雷达测距方程计算确定了理论上探地雷达的最大探测深度与发射频率、地下介质电阻率、介电常数之间的关系,并根据电磁波反射理论计算满足冻土带天然气水合物探测深度所需的系统增益;随后通过低频探地雷达分辨率计算和仿真模拟来确定低频探地雷达在大尺度(200 m)范围的广义分辨率;最后参考已经发现天然气水合物的木里地区基本情况设计冻土及天然气水合物模型,利用时间域有限差分(FDTD)方法进行二维正演,获得了探地雷达信号在冻土带底界以及天然气水合物顶、底界的反射特征,为野外实测数据的处理及解释提供有用信息。研究结果表明,采用中心频率小于等于15 MHz且系统增益大于165 dB的低频探地雷达在地表电阻率较高的冻土区能够满足天然气水合物储层的探测深度要求;分辨率计算及仿真模拟表明低频探地雷达在满足一定条件下在200 m深度可以达到探测深度1%的广义分辨率;探地雷达信号在冻土底界、天然气水合物顶、底界均存在明显的强振幅和频率突变特征;理论计算结果认为应用低频探地雷达直接探测冻土带天然气水合物是可行的。     

探地雷达空气回波特点与处理方法

探地雷达发射的电磁波在整个空间传播,存在空气中回波,空气中回波可分为以下3种：直达波、系统振铃、反射回波。直达波位于探地雷达记录的初期很小时间段,对识别地下介质反射影响不大,系统振铃和地表反射体的回波是探地雷达探地工作的主要干扰。空气中反射体的反射回波时距曲线一般有两种形式：双曲线型、线型。可以通过计算介质中电磁波波速来识别反射回波是空气中反射体形成的,还是地下介质反射形成的。应用水平背景移除、二维滤波可以有效滤除探测剖面中的水平和倾斜同向轴干扰信号;利用地下介质和空气中雷达波速进行偏移处理的资料进行对比解释可以有效提高解释的正确性。     

浅议延庆县木化石自然保护区雷达探测木化石试验研究

本文介绍了延庆木化石自然保护区的地质条件及木化石出露的地层层位,通过探地雷达探测试验,总结了探地雷达方法用于木化石探测的可行性和有效性,提出了探地雷达法在此项应用中的不足和需要完善的方向。     

地质雷达在地下埋藏物检测中的应用研究

运用地质雷达的理论办法,了解某区域范围内已知埋藏物所造成的地质污染情况,以便为下一步布置工程工作和环境保护提供依据。这里还建立了用于区域污染识别的探地雷达探测数据处理模型,对地下污染情况进行了探测和识别,并与实际结果进行了比较。实践证明,该方法既可以提高探地雷达信号解释精度,又提高了工作效率。     

物探方法在浅源石油烃类污染探测中的应用

应用探地雷达和高密度电阻率法,在冀中平原中部某典型石油烃类污染场地进行探测,得到了浅源石油烃类污染物的异常特征。通过对探地雷达和高密度电法资料的分析,得出石油烃类污染物呈现低电阻率、低介电常数特性,根据这个特点圈定出了此污染场地内储油池区域的污染扩散晕。实践证明,这两种物探组合在此类污染场地探测中具有推广价值。     

探地雷达物理模拟相似性准则及监测油气污染试验

利用探地雷达研究油气污染问题是探地雷达应用研究的前沿课题之一。在推导雷达波模型实验的相似性准则的基础上,制作了砂质模型,并以原油为污染材料进行了探地雷达监测油气污染的模型实验。证明探地雷达方法能有效地解决油气污染的范围和油气污染的强度问题。同时为开展下一步实验和野外工作提供了指导。     

Magnetic and ground probing radar measurements for soil pollution mapping in the industrial area of Val Basento (Basilicata Region, Southern Italy): a case study

The joint application of electromagnetic techniques for near-surface exploration is a useful tool for soil pollution monitoring and can also contribute towards describing the spatial distribution of pollutants. The results of a geophysical field survey that was carried out for characterizing the heavy metal and waste disposal soil pollution phenomena in the industrial area of Val Basento (Basilicata region, Southern Italy) are presented here. First, topsoil magnetic susceptibility measurements have been carried out for defining the spatial distribution of superficial pollution phenomena in the investigated area. Second, detailed and integrated measurements based on a high-resolution magnetic mapping and ground probing radar (GPR) profiling have been applied to investigate the subsurface in two industrial areas located in more polluted sites that were identified during the first phase. Our monitoring strategy discloses the way to rapidly define the zone characterized by high pollution levels deriving from chemical industries and traffic emissions and to obtain the way information about the presence of local buried sources of contamination.     

Ground penetrating radar imaging and time-domain modelling of the infiltration of diesel fuel in a sandbox experiment

Ground penetrating radar (GPR) is a non-destructive method which, over the past 10 years, has been successfully used not only to estimate the water content of soil, but also to detect and monitor the infiltration of pollutants on sites contaminated by light non-aqueous phase liquids (LNAPL). We represented a model water table aquifer (72 cm depth) by injecting water into a sandbox that also contains several buried objects. The GPR measurements were carried out with shielded antennae of 900 and 1200 MHz, respectively, for common mid point (CMP) and constant offset (CO) profiles. We extended the work reported by Loeffler and Bano by injecting 100 L of diesel fuel (LNAPL) from the top of the sandbox. We used the same acquisition procedure and the same profile configuration as before fuel injection. The GPR data acquired on the polluted sand did not show any clear reflections from the plume pollution; nevertheless, travel times are very strongly affected by the presence of the fuel and the main changes are on the velocity anomalies. We can notice that the reflection from the bottom of the sandbox, which is recorded at a constant time when no fuel is present, is deformed by the pollution. The area close to the fuel injection point is characterized by a higher velocity than the area situated further away. The area farther away from the injection point shows a low velocity anomaly which indicates an increase in travel time. It seems that pore water has been replaced by fuel as a result of a lateral flow. We also use finite-difference time-domain (FDTD) numerical GPR modelling in combination with dielectric property mixing models to estimate the volume and the physical characteristics of the contaminated sand.     

Tracing leachates at waste sites using geophysical and geochemical modelling

Tracing leachates at landfills is usually carried out using either geophysical methods or chemical analyses of groundwater. There are often problems with fingerprinting pollution sources or clarifying the spreading pattern due to a wide variety of possibilities giving similar anomalies. The aims of the project were to evaluate the advantages of combining results from multigeophysical modelling and statistical/chemical modelling in order to identify pollution sources and the spreading pattern and to test a new technique for chemical fingerprinting. The project was carried out at a landfill in central Sweden using geophysical measurements and modelling of CVES, GPR and VLF as well as chemical modelling using M3 (multivariate mixing and mass balance calculations). The results indicate that by combining geophysical modelling and chemical calculations, the possibilities of fingerprinting the origin of pollution as well as delineating the spreading pattern are significantly increased.     

冰封期水动力水质模型在松花江水污染事件中的应用

根据研究流域特点建立了冰封期水动力水质模型,结合冰封期水位测量的特点,对水位模拟结果进行了修正,分别利用2006和2007年水文监测数据对模型进行了率定和验证,利用模型对2005年松花江硝基苯水污染事件进行模拟。计算结果表明:建立的冰封期水动力水质模型能够很好地适用于该地区,部分断面硝基苯质量浓度峰值的相对误差为5%~13%,峰值出现时间的绝对误差为2~3 h。利用模型预测了上游边界流量增加20%及减少5%对水质的影响,结果表明:流量增加导致污染团峰值提前22 h到达摆渡河断面,硝基苯质量浓度峰值降低了15%,流量减少导致峰值延迟6 h到达摆渡河断面,质量浓度峰值升高了4.6%。     

Geophysical Surveys over Karst Recharge Features,Illinois,USA

Karst aquifers supply a significant fraction of the world's drinking water. These types of aquifers are alsohighly susceptible to pollution from the surface with recharge usually occurring through fractures and solution openings at the bedrock surface. Thickness of the protective soil cover, macropores and openings within the soil cover, and the nature of the weathered bedrock surface all influence infiltration. Recharge openings at the bedrock surface, however, are often covered by unconsolidated sediments, resulting in the inadvertent placement of landfills, unregulated dump sites, tailing piles, waste lagoons and septic systems over recharge zones. In these settings surface geophysical surveys, calibrated by a few soil cores, could be employed to identify these recharge openings, and qualitatively assess the protection afforded by the soil cover. In a test of this hypothesis, geophysical measurements accurately predicted the thickness of unconsolidated deposits overlying karstic dolomite at a site ab     

配位体对地下环境中Fe（Ⅱ）衰减硝基苯的强化作用

通过静态实验研究了配位体对地下环境中Fe（Ⅱ）衰减硝基苯的影响。实验结果表明,配位体的种类、浓度均对Fe（Ⅱ）衰减硝基苯有重要影响。在Fe（Ⅱ）浓度为5 mmol/L的条件下,以半胱氨酸为配位体形成的络合物对硝基苯衰减效果最好,对硝基苯的去除率为86.16%;在配位体浓度变化的条件下,配位体浓度为50 mmol/L时,对硝基苯的衰减效果相对较好,去除率均在65%以上;另外,在Fe（Ⅱ）和配位体浓度一定的条件下,硝基苯的浓度对其衰减也有影响,100 mg/L的硝基苯衰减效果最好,之后随着硝基苯浓度增加,衰减效果呈现逐渐变差的趋势;在Fe（Ⅱ）的络合物衰减硝基苯的过程中,Fe（Ⅱ）被氧化成Fe（Ⅲ）。     

Requirements for the performance of a ground-penetrating radar system in searching for cavities

The requirements for the performance of a ground-penetrating radar (GPR) system for detecting subsurface cavities are analyzed by numerical modeling of the GPR problem. The algorithm used to solve the forward GPR problem is approximated to a real experiment with regard to the design of the GPR system, the parameters of the source and receiver, and their position relative to the medium under study and its inhomogeneity. We calculated the spatiotemporal distribution of the field of the detected signal from a pulse source located at the interface between the medium and a cavity anomaly of a given geometry. The results were used to estimate the dynamic range of the GPR system necessary for determining the anomaly. We also performed GPR surveys of low-contrast inhomogeneities (cavities in mines) using GROT 12 GPR systems and analyzed the survey results by numerical modeling. It is shown that the GPR performance required to detect and locate inhomogeneities of interest at a certain sounding depth can be estimated in the experiment design phase.     

差分GPS实现探地雷达图像地形校正方法研究

针对在地形起伏较大的区域探地雷达获取的图像不能表达地形变化的缺点,通过探地雷达与差分GPS同步采集记录数据,实现探地雷达图像与GPS数据时间同步,选择某一标准水准面为参考面,根据时间位移和线性插值方法,将探地雷达数据进行时深转换,从而实现探地雷达地形校正。探地雷达图像地形校正前后对比表明此方法在保留地下介质体水平方向分布特征的同时,实现了探地雷达图像在垂直方向的精确校正,对地下目标的解译和精确定位有很大的帮助,对浅层活动断层探测具有一定的实际意义。      

探地雷达在隐伏岩溶勘察中的应用

在介绍探地雷达(GPR)方法原理基础上,根据岩溶发育特征及其地球物理性质,总结了GPR反射波特征,结合在岩溶发育区成功应用GPR技术方法的工程勘察实例,说明GPR方法是岩溶区岩土工程勘察和评价的有效手段。