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1.
Crosshole ground penetrating radar (GPR) tomography has been widely used and has the potential to improve the obtained subsurface models due to its high spatial resolution compared to other methods. Recent advances in full-waveform inversion of crosshole GPR data show that higher resolution images can be obtained compared to conventional ray-based GPR inversion because it can exploit all information present in the observed data. Since the first application of full-waveform inversion on synthetic and experimental GPR data, the algorithm has been significantly improved by extending the scalar to a vectorial approach, and changing the stepped permittivity and conductivity update into a simultaneous update. Here, we introduce new normalized gradients that do not depend on the number of sources and receivers which enable a comparison of the gradients and step lengths for different crosshole survey layouts. An experimental data set acquired at the Boise Hydrogeophysics Research Site is inverted using different source–receiver setups and the obtained permittivity and conductivity images, remaining gradients and final misfits are compared for the different versions of the full-waveform inversion. Moreover, different versions of the full-waveform inversion are applied to obtain an overview of all improvements. Most improvements result in a reducing final misfit between the measured and synthetic data and a reducing remaining gradient at the final iteration. Regions with relatively high remaining gradient amplitudes indicate less reliable inversion results. Comparison of the final full-waveform inversion results with Neutron–Neutron porosity log data and capacitive resistivity log data show considerably higher spatial frequencies for the logging data compared to the full-waveform inversion results. To enable a better comparison, we estimated a simple wavenumber filter and the full-waveform inversion results show an improved fit with the logging data. This work shows the potential of full-waveform inversion as an advanced method that can provide high resolution images to improve hydrological models. 相似文献
2.
Time-lapse geophysical data acquired during transient hydrological experiments are being increasingly employed to estimate subsurface hydraulic properties at the field scale. In particular, crosshole ground-penetrating radar (GPR) data, collected while water infiltrates into the subsurface either by natural or artificial means, have been demonstrated in a number of studies to contain valuable information concerning the hydraulic properties of the unsaturated zone. Previous work in this domain has considered a variety of infiltration conditions and different amounts of time-lapse GPR data in the estimation procedure. However, the particular benefits and drawbacks of these different strategies as well as the impact of a variety of key and common assumptions remain unclear. Using a Bayesian Markov-chain-Monte-Carlo stochastic inversion methodology, we examine in this paper the information content of time-lapse zero-offset-profile (ZOP) GPR traveltime data, collected under three different infiltration conditions, for the estimation of van Genuchten–Mualem (VGM) parameters in a layered subsurface medium. Specifically, we systematically analyze synthetic and field GPR data acquired under natural loading and two rates of forced infiltration, and we consider the value of incorporating different amounts of time-lapse measurements into the estimation procedure. Our results confirm that, for all infiltration scenarios considered, the ZOP GPR traveltime data contain important information about subsurface hydraulic properties as a function of depth, with forced infiltration offering the greatest potential for VGM parameter refinement because of the higher stressing of the hydrological system. Considering greater amounts of time-lapse data in the inversion procedure is also found to help refine VGM parameter estimates. Quite importantly, however, inconsistencies observed in the field results point to the strong possibility that posterior uncertainties are being influenced by model structural errors, which in turn underlines the fundamental importance of a systematic analysis of such errors in future related studies. 相似文献
3.
Ground-penetrating radar (GPR) is an effective tool for imaging the spatial distribution of water content. An artificial groundwater recharge test was conducted in Nagaoka City in Japan, and time-lapse crosshole GPR data were collected to monitor the infiltration process in the vadose zone. Since electromagnetic wave velocities in the vadose zone are largely controlled by variations in water content, an increase in traveltime is interpreted as an increase in saturation. In the test zone, the infiltrated water penetrated downward with an average velocity of about 2.7 m/h. A finite-difference time-domain method using two-dimensional cylindrical coordinates is applied to simulate radargrams associated with the advancing wetting front and to quantify the effects of critical refraction. Standard zero-offset profiling for which all first-arrivals are assumed to be direct waves results in an underestimation of water content in the transition zone above the wetting front. As a result, correct velocity analysis requires identification of first-arriving critically refracted waves from the traveltime profile to accurately determine a water content profile. 相似文献
4.
The travel time and amplitude of ground-penetrating radar (GPR) waves are closely related to medium parameters such as water content, porosity, and dielectric permittivity. However, conventional estimation methods, which are mostly based on wave velocity, are not suitable for real complex media because of limited resolution. Impedance inversion uses the reflection coefficient of radar waves to directly calculate GPR impedance and other parameters of subsurface media. We construct a 3D multiscale stochastic medium model and use the mixed Gaussian and exponential autocorrelation function to describe the distribution of parameters in real subsurface media. We introduce an elliptical Gaussian function to describe local random anomalies. The tapering function is also introduced to reduce calculation errors caused by the numerical simulation of discrete grids. We derive the impedance inversion workflow and test the calculation precision in complex media. Finally, we use impedance inversion to process GPR field data in a polluted site in Mongolia. The inversion results were constrained using borehole data and validated by resistivity data. 相似文献
5.
《Journal of Applied Geophysics》2007,61(1):16-38
Unstable rocky slopes are major hazards to the growing number of people that live and travel though mountainous regions. To construct effective barriers to falling rock, it is necessary to know the positions, dimensions and shapes of structures along which failure may occur. To investigate an unstable mountain slope distinguished by numerous open fracture zones, we have taken advantage of three moderately deep (51.0–120.8 m) boreholes to acquire geophysical logs and record single-hole radar, vertical radar profiling (VRP) and crosshole radar data. We observed spallation zones, displacements and borehole radar velocity and amplitude anomalies at 16 of the 46 discontinuities identified in the borehole optical televiewer images. The results of the VRP and crosshole experiments were disappointing at our study site; the source of only one VRP reflection was determined and the crosshole velocity and amplitude tomograms were remarkably featureless. In contrast, much useful structural information was provided by the single-hole radar experiments. Radar reflections were recorded from many surface and borehole fracture zones, demonstrating that the strong electrical property contrasts of these features extended some distance into the adjacent rock mass. The single-hole radar data suggested possible connections between 6 surface and 4 borehole fractures and led to the discovery of 5 additional near-surface fracture zones. Of particular importance, they supplied key details on the subsurface geometries and minimum subsurface lengths of 8 of the 10 previously known surface fracture zones and all of the newly discovered ones. The vast majority of surface fracture zones extended at least 40–60 m into the subsurface, demonstrating that their depth and surface dimensions are comparable. 相似文献
6.
Joseph Holden 《地球表面变化过程与地形》2004,29(4):437-442
Soil pipes are common and important features of many catchments, particularly in semi‐arid and humid areas, and can contribute a large proportion of runoff to river systems. They may also signi?cantly in?uence catchment sediment and solute yield. However, there are often problems in ?nding and de?ning soil pipe networks which are located deep below the surface. Ground‐penetrating radar (GPR) has been used for non‐destructive identi?cation and mapping of soil pipes in blanket peat catchments. While GPR can identify subsurface cavities, it cannot alone determine hydrological connectivity between one cavity and another. This paper presents results from an experiment to test the ability of GPR to establish hydrological connectivity between pipes through use of a tracer solution. Sodium chloride was injected into pipe cavities previously detected by the radar. The GPR was placed downslope of the injection points and positioned on the ground directly above detected soil pipes. The resultant radargrams showed signi?cant changes in re?ectance from some cavities and no change from others. Pipe waters were sampled in order to check the radar results. Changes in electrical conductivity of the pipe water could be detected by the GPR, without data post‐processing, when background levels were increased by more than approximately twofold. It was thus possible to rapidly determine hydrological connectivity of soil pipes within dense pipe networks across hillslopes without ground disturbance. It was also possible to remotely measure travel times through pipe systems; the passing of the salt wave below the GPR produced an easily detectable signal on the radargram which required no post‐processing. The technique should allow remote sensing of water sources and sinks for soil pipes below the surface. The improved understanding of ?owpath connectivity will be important for understanding water delivery, solutional and particulate denudation, and hydrological and geomorphological model development. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
7.
《Advances in water resources》2004,27(6):583-599
Methods for estimating the parameter distributions necessary for modeling fluid flow and contaminant transport in the shallow subsurface are in great demand. Soil properties such as permeability, porosity, and water retention are typically estimated through the inversion of hydrological data (e.g., measurements of capillary pressure and water saturation). However, ill-posedness and non-uniqueness commonly arise in such non-linear inverse problems making their solutions elusive. Incorporating additional types of data, such as from geophysical methods, may greatly improve the success of inverse modeling. In particular, ground-penetrating radar (GPR) methods have proven sensitive to subsurface fluid flow processes and appear promising for such applications. In the present work, an inverse technique is presented which allows for the estimation of flow parameter distributions and the prediction of flow phenomena using GPR and hydrological measurements collected during a transient flow experiment. Specifically, concepts from the pilot point method were implemented in a maximum a posteriori (MAP) framework to allow for the generation of permeability distributions that are conditional to permeability point measurements, that maintain specified patterns of spatial correlation, and that are consistent with geophysical and hydrological data. The current implementation of the approach allows for additional flow parameters to be estimated concurrently if they are assumed uniform and uncorrelated with the permeability distribution. (The method itself allows for heterogeneity in these parameters to be considered, and it allows for parameters of the petrophysical and semivariogram models to be estimated as well.) Through a synthetic example, performance of the method is evaluated under various conditions, and some conclusions are made regarding the joint use of transient GPR and hydrological measurements in estimating fluid flow parameters in the vadose zone. 相似文献
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9.
Ground penetrating radar (GPR) is currently within the scope of China's Chang-E 3 lunar mission, to study the shallow subsurface of the Moon. In this study, key factors that could affect a lunar GPR performance, such as frequency, range resolution, and antenna directivity, are discussed firstly. Geometrical optics and ray tracing techniques are used to model GPR echoes, considering the transmission, attenuation, reflection, geometrical spreading of radar waves, and the antenna directivity. The influence on A-scope GPR echoes and on the simulated radargrams for the Sinus Iridum region by surface and subsurface roughness, dielectric loss of the lunar regolith, radar frequency and bandwidth, and the distance between the transmit and receive antennas are discussed. Finally, potential scientific return about lunar subsurface properties from GPR echoes is also discussed. Simulation results suggest that subsurface structure from several to hundreds of meters can be studied from GPR echoes at P and VHF bands, and information about dielectric permittivity and thickness of subsurface layers can be estimated from GPR echoes in combination with regolith composition data. 相似文献
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11.
GPR study of pore water content and salinity in sand 总被引：5，自引：0，他引：5
High‐resolution studies of hydrological problems of the near‐surface zone can be better accomplished by applying ground‐probing radar (GPR) and geoelectrical techniques. We report on GPR measurements (500 and 900 MHz antennae) which were carried out on a sorted, clean sand, both in the laboratory and at outdoor experimental sites. The outdoor sites include a full‐scale model measuring 5 × 3 × 2.4 m3 and a salinity site measuring 7.0 × 1.0 × 0.9 m3 with three buried sand bodies saturated with water of various salinities. Our studies investigate the capability of GPR to determine the pore water content and to estimate the salinity. These parameters are important for quantifying and evaluating the water quality of vadose zones and aquifers. The radar technique is increasingly applied in quantifying soil moisture but is still rarely used in studying the problems of water salinity and quality. The reflection coefficient at interfaces is obtained from the amplitude spectrum in the frequency and time domains and is confirmed by 1D wavelet modelling. In addition, the GPR velocity to a target at a known depth is determined using techniques of two‐way traveltime, CMP semblance analysis and fitting an asymptotic diffraction curve. The results demonstrate that the reflection coefficient increases with increasing salinity of the moisture. These results may open up a new approach for applications in environmental problems and groundwater prospecting, e.g. mapping and monitoring of contamination and evaluating of aquifer salinity, especially in coastal areas with a time‐varying fresh‐water lens. In addition, the relationship between GPR velocity and water content is established for the sand. Using this relationship, a subsurface velocity distribution for a full‐scale model of this sand is deduced and applied for migrated radargrams. Well‐focused diffractions separate single small targets (diameter of 2–3 cm, at a depth of 20–180 cm and a vertical interval of 20 cm). The results underscore the high potential of GPR for determining moisture content and its variation, flow processes and water quality, and even very small bodies inside the sand or soil. 相似文献
12.
以ASTM标准规范为基础对探地雷达（Ground Penetrating Radar 以下简称GPR）的地下探测方法的应用做了比较系统的概述，主要内容包括：部分专业术语的解释；测试过程中雷达探测深度及其中心频率、垂直分辨率、水平分辨率等的关系，测试过程中常见的天线移动方式，以及雷达波速的预测几种方法，数据显示方式；雷达数据解释和数据处理的一般过程及方法.目前我国尚没有关于GPR的国家规范或行业标准，文章对GPR的使用及规范的编制具有一定的参考意义. 相似文献
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14.
T. D. L. Irvine‐Fynn B. J. Moorman J. L. M. Williams F. S. A. Walter 《地球表面变化过程与地形》2006,31(7):892-909
In recent years, ground‐penetrating radar (GPR) has been increasingly used for characterization of subglacial and englacial environments at polythermal glaciers. The geophysical method is able to exploit the dielectric difference between water, air, sediment and ice, allowing delineation of subsurface hydrological, thermal and structural conditions. More recent GPR research has endeavoured to examine temporal change in glaciers, in particular the distribution of the cold ice zone at polythermal glaciers. However, the exact nature of temporal change that can be identified using GPR has not been fully examined. This research presents the results of three GPR surveys conducted over the course of a summer ablation season at a polythermal glacier in the Canadian Arctic. A total of approximately 30 km of GPR profiles were collected in 2002 repeatedly covering the lower 2 km of Stagnation Glacier, Bylot Island (72°58′ N 78°22′ W). Comparison between profiles indicated changes in the radar signature, including increased noise, appearance and disappearance of englacial reflections, and signal attenuation in the latter survey. Further, an area of chaotic returns in up‐glacier locations, which was interpreted to be a wet temperate ice zone, showed marked recession over the course of the ablation season. Combining all the temporal changes that were detected by GPR, results indicate that a polythermal glacier may exhibit strongly seasonal changes in hydrological and thermal characteristics throughout the ice body, including the drainage of 17 000 m3 of temporarily stored intra‐glacial meltwater. It is also proposed that the liquid water content in the temperate ice zone of polythermal glaciers can be described as a fraction of a specific retention capacity. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
15.
Zhiwei Xu James Irving Kyle Lindsay John Bradford Peimin Zhu Klaus Holliger 《Geophysical Prospecting》2020,68(2):678-689
Knowledge about the stochastic nature of heterogeneity in subsurface hydraulic properties is critical for aquifer characterization and the corresponding prediction of groundwater flow and contaminant transport. Whereas the vertical correlation structure of the heterogeneity is often well constrained by borehole information, the lateral correlation structure is generally unknown because the spacing between boreholes is too large to allow for its meaningful inference. There is, however, evidence to suggest that information on the lateral correlation structure may be extracted from the correlation statistics of the subsurface reflectivity structure imaged by surface-based ground-penetrating radar measurements. To date, case studies involving this approach have been limited to 2D profiles acquired at a single antenna centre frequency in areas with limited complementary information. As a result, the practical reliability of this methodology has been difficult to assess. Here, we extend previous work to 3D and consider reflection ground-penetrating radar data acquired using two antenna centre frequencies at the extensively explored and well-constrained Boise Hydrogeophysical Research Site. We find that the results obtained using the two ground-penetrating radar frequencies are consistent with each other, as well as with information from a number of other studies at the Boise Hydrogeophysical Research Site. In addition, contrary to previous 2D work, our results indicate that the surface-based reflection ground-penetrating radar data are not only sensitive to the aspect ratio of the underlying heterogeneity, but also, albeit to a lesser extent, to the so-called Hurst number, which is a key parameter characterizing the local variability of the fine-scale structure. 相似文献
16.
本文以地铁深基坑岩体边坡为研究对象,采用弹性波CT初步判断基坑岩体病害的类型及空间分布并辅以地质雷达进行验证;进而用分水岭算法分析弹性波CT获得的波速分布,以提取病害处的细部声速变化,圈定病害范围;在此基础上,以弹性波CT三维空间波速数据库的坐标信息为基础,结合分水岭算法得到的空间坐标信息获得建模数据库,导入GOCAD... 相似文献
17.
Water balance estimation under the challenge of data scarcity in a hyperarid to Mediterranean region 
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下载免费PDF全文 Agnes Sachse Christian Fischer Jonathan B. Laronne Hanna Hennig Amer Marei Olaf Kolditz Tino Rödiger 《水文研究》2017,31(13):2395-2411
Water budget analyses are important for the evaluation of the water resources in semiarid and arid regions. The lack of observed data is the major obstacle for hydrological modelling in arid regions. The aim of this study is the analysis and calculation of the natural water resources of the Western Dead Sea subsurface catchment, one which is highly sensitive to rainfall resulting in highly variable temporal and spatial groundwater recharge. We focus on the subsurface catchment and subsequently apply the findings to a large‐scale groundwater flow model to estimate the groundwater discharge to the Dead Sea. We apply a semidistributed hydrological model (J2000g), originally developed for the Mediterranean, to the hyperarid region of the Western Dead Sea catchment, where runoff data and meteorological records are sparsely available. The challenge is to simulate the water budget, where the localized nature of extreme rainstorms together with sparse runoff data results in few observed runoff and recharge events. To overcome the scarcity of climate input data, we enhance the database with mean monthly rainfall data. The rainfall data of 2 satellites are shown to be unsuitable to fill the missing rainfall data due to underrepresentation of the steep hydrological gradient and temporal resolution. Hydrological models need to be calibrated against measured values; hence, the absence of adequate data can be problematic. Therefore, our calibration approach is based on a nested strategy of diverse observations. We calculate a direct surface runoff of the Western Dead Sea surface area (1,801 km2) of 3.4 mm/a and an average recharge (36.7 mm/a) for the 3,816 km2 subsurface drainage basin of the Cretaceous aquifer system. 相似文献
18.
Mapping the spatial variation of soil water content at the field scale with different ground penetrating radar techniques 总被引：2，自引：0，他引：2
L. Weihermüller J.A. Huisman S. Lambot M. Herbst H. Vereecken 《Journal of Hydrology》2007,340(3-4):205-216
Two ground penetrating radar (GPR) techniques were used to estimate the shallow soil water content at the field scale. The first technique is based on the ground wave velocity measured with a bistatic impulse radar connected to 450 MHz ground-coupled antennas. The second technique is based on inverse modeling of an off-ground monostatic TEM horn antenna in the 0.8–1.6 GHz frequency range. Data were collected on a 8 by 9 m partially irrigated intensive research plot and along four 148.5 m transects. Time domain reflectometry, capacitance sensors, and volumetric soil samples were used as reference measurements. The aim of the study was to test the applicability of the ground wave method and the off-ground inverse modeling approach at the field scale for a soil with a silt loam texture. The results for the ground wave technique were difficult to interpret due to the strong attenuation of the GPR signal, which is related to the silt loam texture at the test site. The root mean square error of the ground wave technique was 0.076 m3 m−3 when compared to the TDR measurements and 0.102 m3 m−3 when compared with the volumetric soil samples. The off-ground monostatic GPR measured less within-field soil water content variability than the reference measurements, resulting in a root mean square error of 0.053 m3 m−3 when compared with the TDR measurements and an error of 0.051 m3 m−3 when compared with the volumetric soil samples. The variability between the two GPR measurements was even larger with a RSME of 0.115 m3 m−3. In summary, both GPR methods did not provide adequate spatial information on soil water content variation at the field scale. The main reason for the deviating results of the ground wave method was the poor data quality due to high silt and clay content at the test site. Additional reasons were shallow reflections and the dry upper soil layer that cannot be detected by the ground wave method. In the case of off-ground GPR, the high sensitivity to the dry surface layer is the most likely reason for the observed deviations. The off-ground GPR results might be improved by using a different antenna that allows data acquisition in a lower frequency range. 相似文献
19.
Paulo Roberto Antunes Aranha Cristina Helena Ribeiro Rocha Augustin Frederico Garcia Sobreira 《Journal of Applied Geophysics》2002,49(4)
Ground penetrating radar (GPR) has been used as a tool to access information about ground subsurface features. Such information is very important for different types of studies, varying from those related to archeological research to those studying geological elements of bedrock. More recently, however, GPR has been increasingly applied to environmental studies, especially for soil research. This paper presents the results of an application of GPR for the study of weathered profiles. GPR was used to discover the degree of trustworthiness of the information on the ground subsurface through the interpretation of the results of the radar sections as well as the data collected from boreholes, which reached until 21 m. The results show a relatively high degree of details obtained by GPR, indicating the possibility of speeding up ground subsurface surveys related to geomorphological, geological, and pedological studies. 相似文献
20.
《Journal of Applied Geophysics》1999,41(1):19-30
Optimal electromagnetic wave propagation velocities and subsurface images for ground-penetrating radar (GPR) data can be specified by using an imaging scanning method. In addition to time-migrating the unmigrated GPR section, we remigrate the already time-migrated section by a one-step remigration operator using different velocities. This creates many time-migrated images for different constant migration velocities. In this way, the computation time for time-migration is very much reduced. Time-migrated reflector images `propagate' when the constant migration velocity is continuously changed. For this `propagation' there exists a wave-equation-type partial differential equation. Each time-migrated section can thus be viewed as a snapshot for a certain migration velocity. The time-migrated reflector images behave like `waves', called image waves. This is applied to real GPR data acquired over a concrete body within which a steel cable frame is buried. The method produces a quick velocity scan to find a reliable migration velocity leading to the best time-migrated image. 相似文献