Estimation of Hydraulic Property of an Unconfined Aquifer by GPR

Controlled water productions were performed at a water source area of Ulaanbaatar city, Mongolia to evaluate the effectiveness of ground penetrating radar (GPR) for detecting and monitoring dynamic groundwater movements in the subsurface and for estimating the hydraulic properties of the aquifer. Field experiments in Ulaanbaatar were carried out in 2001 and 2002. GPR data were acquired using 100 MHz antennas. This paper reports the results of GPR methods to monitor the groundwater migration caused by the pumping operation and GPR’s potential ability to estimate hydraulic properties of the aquifer. The GPR data sets were acquired very carefully by locating the antenna position accurately. The residual trace shows a feature that is a combination of the water level reflections acquired at two different times in the pumping test. It helped to determine travel time and its effective reflection point from the top of the water saturated zone. The residual wavelet varies versus offset from the pumping well for a given residual image. Common midpoint (CMP) data and velocity analysis indicated the depth of the water table and the water content in the unsaturated and saturated zone. Combining hydrogeologic data with quantitative information yielded by GPR data, hydraulic properties of the aquifer could be estimated by assuming a hydraulic model. It was concluded that GPR can be successfully employed to monitor groundwater migration and to estimate hydraulic properties of the aquifer.     

Measuring and Modeling of Direct Ground Wave Depth Penetration Under Transient Soil Moisture Conditions

This study represents the first attempt to investigate the GPR direct ground wave sampling depth by comparing GPR estimated soil moisture contents with data from horizontally and vertically installed time domain reflectometry (TDR) probes at different depths. The GPR direct ground wave method (200 MHz centre frequency) was used to estimate the temporal soil moisture dependence during uniform irrigation and drainage. Uniform irrigation and drainage experiments were conducted in an experimental pit (2.5 × 1.0 × 0.8 m) filled with repacked sandy loam soil. The GPR moisture contents measurements were more consistent with the moisture contents from vertically installed TDR than horizontally installed TDR. An analytical solution for one-dimensional drainage of water was used to estimate the change in GPR ground wave sampling depth during drainage. The analytical solution was first fit to vertical TDR data to obtain an estimate of the soil hydraulic parameters and the GPR sampling depth was then estimated by fitting the drainage solution to the measured GPR data. The GPR direct ground wave sampling depth using the analytical solution during drainage varied from −20 cm at high moisture content to −50 cm at the lowest moisture content.     

在线监测液压系统油液污染度的一种方法

针对液压系统油液中,固体杂质、水等污染物的存在而导致液压元件失效的问题,设计了液压油污染度的在线监测装置,通过找出影响液压油电导率变化的因素,监测液压油电导率的变化,实现了对油液中固体杂质含量和水含量的在线监测,为系统的主动维修提供了可靠数据。     

Frequency Dependence of the Soil Electromagnetic Properties Derived from Ground-Penetrating Radar Signal Inversion

The accuracy at which the subsurface electromagnetic properties can be identified from full wave inversion of ground penetrating radar (GPR) signals relies on the appropriateness of the model describing their frequency dependence. In this paper, we focus on the characterization of the frequency dependence of the dielectric permittivity and electric conductivity of a sandy soil subject to different water contents from inversion of GPR measurements. Based on previous studies of Lambot et al. the methodology relies on an ultrawide band (UWB) stepped-frequency continuous-wave (SFCW) radar combined with an off-ground monostatic transverse electromagnetic (TEM) horn antenna. Forward modeling of the radar signal is based on linear system transfer functions for describing the antenna, and on the exact solution of Maxwells equations for wave propagation in a horizontally multilayered medium representing the subsurface. Model inversion, formulated by the classical least-squares problem, is carried out iteratively using advanced global optimization techniques. The frequency dependence of the electromagnetic properties of the sandy soil is characterized by performing inversions of the radar signal in different and subsequent limited frequency bands, in which the electromagnetic parameters are assumed to be constant. We observed that over the entire frequency band considered in this study (1–3 GHz), the dielectric permittivity of the sand remains constant with frequency, whatever the water content is. In contrast, the electric conductivity increases significantly from 1GHz to 3 GHz, and this effect increases with water content. The frequency dependence of the electric conductivity may be adequately described using a simple linear relationship. This approach is advantageous since it limits the number of parameters to be optimized in the inverse modeling procedure.     

土壤电导率测量系统开发

介绍一种基于“电流一电压四端法”的土壤电导率测量系统的开发。该测量系统由传感器单元、数据采集器USB2808和计算机软件等部分组成。传感器单元包括4个电极,2个外侧电极用来向土壤中输入交流恒流激励信号,2个内侧电极用来检测与土壤电导率相关的电压降。数据采集器USB2808用来将传感器测得的模拟电压信号转换为数字电压信号。计算机软件使用VC＋＋来开发人机交互界面,实现了输入恒流值、内侧电极电压降、土壤电导率等值的显示,并可将这些值保存到数据库中。试验结果表明该测量系统可以有效输出土壤电导率的值。     

The measurement of discharge using a commercial digital video camera in irrigation canals

This paper presents measurements of the discharge by image techniques on the surface velocity field and water stage in irrigation canals. The velocity and stage gauge are obtained from a commercial digital video camera. The time series of the surface velocity and stage were collected simultaneously. Particle image velocimetry (PIV) was used to determine the surface velocities in the irrigation canal. PIV proceeds by using bubbles floating on the water surface as tracer particles, and making a cross-correlation analysis between two continuous images. The whole surface velocity distribution in the irrigation canals can be obtained. The water stage of the canal is obtained from the digital video camera images by making use of image segments to separate the stage gauge and the background. The discharge is computed by using the surface velocities and water stage via open channel velocity distribution theory. Comparing the discharge measured using image techniques with Parshall flume data shows that the differences are less then 5%. The results suggest that the image measurement techniques developed can be used in applications to estimate the discharge in irrigation canals effectively.     

Measurement of the solids volume fraction and velocity distributions in solids–liquid flows using dual-plane electrical resistance tomography

This paper describes a dual-plane Electrical Resistance Tomography (ERT) system for measuring the local solids volume fraction distribution and the local solids axial velocity distribution in solids–liquid flows. The paper also describes a local, intrusive conductivity probe system for providing reference measurements of the distributions obtained using the dual-plane ERT system. Experiments were performed using both the ERT system and the local probe system in vertically upward and inclined solids–water flows. Good agreement between the two techniques was observed. The local solids volume fraction distribution and the local solids axial velocity distribution obtained using the ERT system enable good estimates to be made of the mean solids volume fraction, the mean solids velocity and the solids volumetric flow rate.     

Operative Calibration Methodology of a TDR Sensor for Soil Moisture Monitoring under Irrigated Crops

Time domain reflectometry (TDR) is more and more frequently used for soil water content measurements in replacement of other techniques as neutron probe. Such observations that can be continuously collected on dataloggers are convenient for monitoring water fluxes under irrigated crops. Though relationships to calculate volumetric water content from analysis of TDR signal and collected data are published in literature or given by manufacturers for different commercialized devices, the results are not satisfactory for many soils and specific calibrations are required. In replacement of the traditional calibration method, two rapid operative computer assisted methods are proposed. The first one is based on drip moistening of a cylindrical sample of disturbed dry soil in which a TDR sensor is vertically embedded. The second one uses the same cylindrical sample wetted close to saturation in which a TDR sensor is inserted step by step during measurements. The data from the two methods were fitted using second degree models. These results are in good agreement with conventional calibration method or gravimetric field measurements of soil water content. Utilization of short time step TDR measurements for monitoring soil water storage under a furrow irrigated corn shows consistent observations with water applications or uptakes by crop. Field comparison with neutron probe and gravimetric measurements corroborate the need of a specific calibration for the soil studied in this paper though its clay content is about 20%.     

Determination of the Bingham parameters of an electrorheological fluid in an axial flow concentric-cylinder rheometer

Electrorheological (ER) fluids are fluids that undergo changes in their rheological properties in the presence of an applied electrical field. The change in the flow properties with an applied electrical field has led to their being investigated for use as ‘smart’ lubricants. The Bingham model is currently used to describe the behaviour of these fluids. In this work, the Bingham model parameters of a commercially available ER fluid are obtained using an axial flow concentric-cylinder rheometer. Two methods are used to determine these parameters. One is the Weissenberg (—Rabinowitsch) method applied to thin annular slits, to obtain corrected stress—strain rate information. The other method involves directly fitting the velocity—pressure curve data to the axial flow rate equation of a Bingham fluid through concentric cylinders. The results obtained by these two methods differ by as much as 49.4 and 63.5% for the yield stress and viscosity, respectively. It is observed for this ER fluid that the yield stress increases according to a power law relationship with the applied electrical field. The viscosity appears to decrease linearly with an increase in the applied electrical field.     

Electrical resistivity and conductivity of greases: An initial study

Investigations of railway wagons fitted with rolling‐element bearings have shown damage to the bearings from the passage of electric current. This also occurs in railway wagons without an electric energy consumption of their own, because of residual currents from electric locomotives. This phenomenon gives rise to technical, financial, and even safety problems. This paper reviews research in the field of rolling‐element bearings exposed to electric currents. The paper also reports on an ongoing study undertaken to understand the mechanism of current flow and the role of lubricants in the associated damage, and to identify the possibilities of minimising bearing damage. The obvious solution to this problem is to use optimised greases, i.e., with high electrical conductivity and good lubricating ability. In the preliminary work reported here a number of greases for railway use were tested to determine their electrical conductivity in static and dynamic situations. These tests were performed using specially designed apparatus, and significant initial information about the electrical properties of greases has been obtained in this research, for example, that there is a correlation between the electrical conductance under static and dynamic conditions. All the greases tested showed comparatively high resistivity values, which could be one explanation for the bearing damage observed.     

综合物探法在场地地基土勘察中的应用

物探方法由于其高效、无损的特点,已经广泛应用于场地地基土的勘察中。然而,由于单一物探方法的限制,综合物探的思想就显得尤为重要。文章结合工程实例,以高密度电法与探地雷达为例,在介绍其方法原理与工作方式的基础上,说明了物探方法综合应用在地基土勘察中的效果。     

Analysis of Linear Prediction for Soil Characterization in GPR Data for Countermine Applications

Ground-penetrating radar (GPR) is a versatile technology for subsurface sensing, and has shown promise in countermine applications when a target detection algorithm is employed. Because the soil environment is naturally heterogeneous and nonstationary, many detection algorithms have taken the form of adaptive filters operating on the real-aperture radar data. In particular, linear prediction techniques have received much attention for their ability to screen for anomalous signals that differ from the background. In this work, we demonstrate that linear prediction may provide a low-dimensional feature set that is indicative of various soil properties. Experiments were performed with simulated and field-collected GPR data, and results provide greater understanding of how linear predictors might be useful in landmine detection over varying terrain.     

Characterizing Subsurface Archaeological Structures with Full Resolution 3D GPR at the Early Dynastic Foundations of Saqqara Necropolis,Egypt

Currently, Ground Penetrating Radar (GPR) used in archaeological prospection is based on 2-D parallel line methodologies characterized by line spacing from 0.25 to 1 m (common line separation is 0.5 m) with different GPR antennas and extensive interpolation used to fill data gaps. High resolution 3-D GPR images of the subsurface can be obtained by recording data with a quarter wavelength grid spacing in all directions. Recently, we used a new GPR system which is a combination of commercial GPR with a rotary laser positioning system developed at Tohoku University for full-resolution subsurface imaging. In this paper we will show how the high density 3-D GPR data acquired over an area of about 14 m?×?28 m can improve the image quality and reveal the subsurface archaeological structure of early dynastic foundations in the Saqqara area. The GPR vertical cross-sections and the horizontal depth slices extracted from the full-resolution 3-D GPR reveal great information about ancient human activities, most likely burial mounds. GPR data at depth greater than 1.3 m were overwhelmed by “ringing features” (repeated horizontal harmonic-like features) most probably caused by the presence of underlying shallow layers of low resistivity shale and claystone. A 2-D electric resistivity tomography (ERT) profile was acquired using a multi-electrode system with 1 m electrode spacing. The ERT section shows high resistivity for the near surface desert sand and gravel deposits. The second geoelectric layer detected by ERT shows a low resistivity value consistent with the presence of a highly conductive layer at a depth of about 1.3 m. Integration of such different geophysical tools (e.g. GPR with ERT) helps to interpret the repeated horizontal features in the 3-D GPR data.     

Joint Interpretation of Geophysical Data for Archaeology: A Case Study

Interpret-joints within geophysical data recorded in a complex area where ruins do not outcrop and only earthenware remains within the surficial layer are present. The study area, located in central Italy, consists of Roman, medieval and modern ruins that are included in reworked sediments. The geology is formed by inhomogeneous alluvial sediments (sand and gravel) several meters thick with diamagnetic character. To reduce the ambiguity in the subsurface reconstruction, a joint interpretation of georadar, magnetic and electrical tomography data was performed. The georadar was chosen to reconstruct detailed subsurface features, the electrical tomography to distinguish resistive bodies (stones, voids, etc.) from conductive (cavities filled by clay) and, because of the diamagnetic character of in situ sediments, the magnetic method was chosen to detect the earthenware ruins. The geophysical data were controlled by excavation, which detected silos of 1 m in diameter and a concrete layer at a few centimeters from the topographic surface. Time slices in the georadar data allowed us to detect the silos and to define the lateral edge of the concrete layer. Silos were also indirectly detected by the magnetic data because of the earthenware present in the filling sediments. Electrical tomography detected the concrete layer and an ancient anthropogenic surface of few centimeter depths. The study demonstrates that, because the geophysical methods are based on different physical characteristics, they can have different resolution and therefore detect different bodies.     

Clutter Reduction and Detection of Minelike Objects in Ground Penetrating Radar Data Using Wavelets

Ground Penetrating Radar (GPR) signatures of shallowly buried landmines are normally obscured by a strong background signal comprised of the reflections from the ground surface and the antenna crosstalk. Based on the notion that buried landmine produces an anomaly in the soil dielectric an automated procedure has been developed which detects soil dieletric anomalies of the size comparable to the size of landmine in GPR data and enhances the signatures of such anomalies. A local background estimate is computed and a soil dielectric anomaly is detected at the spatial position where a change from the estimated background signal occurs. A translation invariant wavelet packet decomposition is applied for detection. The computation takes place in a running window which allows for the algorithm to adapt to the variations in ground conditions and antenna height. The technique was tested using a number of minelike targets buried in several different soil environments and the testing results are presented.     

Feasibility study of estimating the porosity of soils from sound absorption measurements

This feasibility study describes a novel method to estimate porosity of soil by measurements of the sound absorption coefficient. Several samples of forest soil were taken and subjected to various environmental treatments to alter their humidity content. Measurements of the sound absorption coefficient were conducted on these samples. The mean sound absorption was then calculated as a single characteristic value. Porosity and volumetric moisture for each sample were determined. The results suggested a very good correlation between porosity and the mean absorption coefficient. The highest absorption values were obtained for samples in dry state, while lowest absorption values were found from samples in a saturated state, confirming the highly determinant effect of porosity on the absorption coefficient. Finally, by means of a statistical analysis, linear coefficients that relate the average absorption coefficient and porosity were determined.     

添加少量纳米SiCp对铜基材料电学和摩擦学性能的影响

考察了添加少量纳米SiCp对铜基材料电学和摩擦学性能的影响。结果表明：添加少量纳米SiCp(体积分数为0．5％),轻微降低了铜基材料的导电率,显著提高了耐磨性,有效降低了铜／钢摩擦副之间的粘着作用和材料转移;130nm SiCp／Cu基复合材料的导电性和耐磨性都优于30nm SiCp／Cu基复合材料。     

Parallel Plates Compared with Conventional Rods as TDR Waveguides for Sensing Soil Moisture

Dielectric methods of estimating the water content of soils, especially TDR, have become accepted as routine measurement techniques. Basic to the TDR technique is the waveguide, which is inserted into the soil for obtaining measurements of the effective soil permittivity, from which water content is estimated. In this study we compare the use of flat stainless steel plates with cylindrical stainless steel rods. We suggest that the use of plates gives a more even distribution of electromagnetic energy within the soil volume sampled and reduces the so called ``skin effect' where the electromagnetic energy is concentrated close to the surface of the electrodes. Plates will not be suitable for all measurement purposes but wherever they can be applied they should result in more representative measurements from the medium under investigation. Calculations of electrical field intensity are presented to compare the relative energy density between the electrodes. Field and laboratory studies were alsoconducted considering some of the practicalities of using the alternative waveguides.     

Adaptive filtering techniques for velocity estimation of tomographic electric capacitance signals of two-phase gas/oil flows

The development of adaptive real-time flow velocity estimation algorithms for two-phase flows can contribute to monitoring the pipelines of various complex processes, such as energy, chemical, petroleum and nuclear industries. Among the different non-invasive tomography techniques, electrical capacitance tomography (ECT) is gaining increasing attention for its potential use in real-time imaging and characterization of multiphase flow systems. The nature of ECT signals for two-phase flows can significantly degrade the velocity estimation process with cross-correlation approaches. We address the unique challenges of such signals and propose a preprocessing technique to improve the performance and robustness of the velocity estimation algorithm. Two adaptive filters are used to estimate the velocity of a two-phase type flow. A least mean square (LMS) and a fast block LMS (FBLMS) are used to model the time delay between the two signals captured by the twin sensor (ECT). Performance of the proposed technique is assessed by applying it to ECT data obtained from an experimental flow rig. The computed estimates are then compared with the calculated velocity from tracking motion of bubbles captured by a high speed camera monitoring the two phase flow in the pipe. Results show that the proposed technique provides consistent results across various flow patterns, and is advantageous compared to cross-correlation based techniques, specially for chaotic flow conditions. Furthermore, the proposed estimation algorithms can be applied to other electric based tomographic techniques.