Analysis Of Ground Penetrating Radar Data Research Articles

Symmetry between Theoretical and Physical Investigation of Water Contamination Using Amplitude Variation with Offset Analysis of Ground-Penetrating Radar Data

We evaluated the symmetry of theoretical and experimental analysis of water contamination such as non-aqueous phase liquid (NAPL) by using amplitude variations with offset analysis (AVO) of ground-penetrating radar (GPR) data. We used both theoretical and experimental approaches for AVO responses of GPR to small distributions of contamination. Theoretical modeling is a tool used to confirm the feasibility of geophysical surveys. Theoretical modeling of NAPL-contaminated sites containing wet sand—both with the water and light non-aqueous phase liquid—was applied by keeping in consideration the GPR AVO analysis in acquisition. Reflectivity was significantly altered with the changes in the contents of water and NAPL during modeling. The wet and dry sands introduced in our model changed two major phenomena: one, the wave pattern—implying a slight phase shift in the wave; and two, an amplitude jump with the dim reflection radar gram observed in the model. Experimental data were collected and analyzed; two observations were recorded during physical data analysis. First, relative permittivity confirmed the presence of NAPL in an experimental tank. Second, reflection patterns with jumps in amplitude and changes in polarity confirmed the theoretical investigation. Our results demonstrate that GPR AVO analysis can be as effective for detection of non-aqueous phase liquid (NAPLs) as it has been used to determine moisture contents in the past. The theoretical and experimental models were in symmetry, and both found a jump in reflection strength. The reflection pattern normally jumped with NAPL-intrusion. From the perspective of water contamination, this study emphasizes the need to take into account the impact of GPR AVO analyses along with the expert’s adaptive capacities.

GPR research on damaged road pavements built in cut and fill sections

We present the GPR (Ground Penetrating Radar) results dealing with flexible road pavements located on cut and fill sections. The aim is to evaluate the road damage (particularly the ramified cracks) taking into consideration also the cut and fill sections height and the traffic load. GPR evaluation was carried out on 14 sites selected in the secondary non-urban road network of L’Aquila, a medium-size urban area of Central Italy. Stress induced by traffic load generally affects a road section thickness of about 1.5 m. A monostatic 1600 MHz GPR antenna was used because it is quite high-resolution when inspecting road damage. GPR acquisition was carried out in damaged and adjoining undamaged road sites, to compare GPR data of the two areas. GPR data analysis was based on the sweep-rectified power approach to evaluate the radar signal attenuation curve vs. depth, which permitted to single out different road types of damage and to discuss the factors which caused them.

CLAY DETECTION IN LAKES OF LATGALE USING GROUND PENETRATING RADAR

The most common method to determine the presence of clay in lakebed is coring method. This method requires survey of the whole lake area using stratified sampling method which is time and physical labour consuming process. To lessen the amount of coring samples and narrow the area of clay survey thus making the whole process faster and more effective, research was made to determine the possibility to indentify clay and its sediments using georadar survey or ground penetrating radar (GPR) method. GPR data analysis and coring studies in lake Zeiļu were used to evaluate GPR as potential method in lake clay sediment research. GPR method was tested in summer and winter during ice-covered period.

Automated visualization of concrete bridge deck condition from GPR data

Ground-penetrating radar (GPR) is one of the most commonly used technologies for condition assessment of concrete bridge decks. However, there have been no fully automated algorithms to visualize the data collected with this technique. In such context, the current paper presents a method for a full automation of GPR data visualization and analysis. Based on the background removal, depth correction, synthetic aperture focusing technique (SAFT), and interpolation algorithms, this automated method produces a plan view map of amplitude of GPR signals. In the obtained map, two types of information are observed at the same time. First, as the strongest reflectors of electromagnetic energy, rebars will appear as the most visible. Second, the areas of corrosive environment and, thus, likely corrosion, will be detected as having low amplitude rebar reflections. As a proof of concept, the proposed method was implemented for two bare concrete bridge decks and two concrete bridge decks with asphalt overlays. In all cases, the results obtained were excellent where the maps pinpointed the areas affected by corrosion. These areas were confirmed by other methods of evaluation, such as electrical resistivity (ER), half-cell potential (HCP), chloride analysis of core samples, or visual inspection. With the demonstrated performance, the proposed method is expected to be an excellent alternative to the available methods of GPR data evaluation and visualization. In the future, it should be improved to provide an indication of corrosion severity/probability at each deck location.

Railway Track Condition Assessment at Network Level by Frequency Domain Analysis of GPR Data

The railway track system is a crucial infrastructure for the transportation of people and goods in modern societies. With the increase in railway traffic, the availability of the track for monitoring and maintenance purposes is becoming significantly reduced. Therefore, continuous non-destructive monitoring tools for track diagnoses take on even greater importance. In this context, Ground Penetrating Radar (GPR) technique results yield valuable information on track condition, mainly in the identification of the degradation of its physical and mechanical characteristics caused by subsurface malfunctions. Nevertheless, the application of GPR to assess the ballast condition is a challenging task because the material electromagnetic properties are sensitive to both the ballast grading and water content. This work presents a novel approach, fast and practical for surveying and analysing long sections of transport infrastructure, based mainly on expedite frequency domain analysis of the GPR signal. Examples are presented with the identification of track events, ballast interventions and potential locations of malfunctions. The approach, developed to identify changes in the track infrastructure, allows for a user-friendly visualisation of the track condition, even for GPR non-professionals such as railways engineers, and may further be used to correlate with track geometric parameters. It aims to automatically detect sudden variations in the GPR signals, obtained with successive surveys over long stretches of railway lines, thus providing valuable information in asset management activities of infrastructure managers.

Quantitative Stability Analysis of Ground Penetrating Radar Systems

The hardware instability of a ground penetrating radar (GPR) system has a severe impact on the quantitative analysis of GPR data, which is aimed for material characterization and subsurface monitoring. In this letter, an instability index is proposed to quantify the stability performance of a GPR system and the influences of the GPR system type, warm-up time, environmental noise, and the antenna vibration on it are evaluated through a series of laboratory experiments on a sandbox model. It is found that the GPR signal recorded by a stepped-frequency GPR system based on a vector network analyzer is much more stable than that by a commercial impulse GPR system at a cost of more sweep time. A warm-up time of several minutes is enough for an impulse GPR system. Environmental noise has a negligible influence on the stability performance of a GPR system. Mechanical vibrations of GPR antennas have a severe impact on the stability performance of the GPR system, and the instability index and timing jitter can be increased by more than one order of magnitude in a vibrating condition over those in a static condition. The instability index of the direct signal has a negligible difference with that of the reflection signal from a metal plate; thus, a simple measurement of direct signal on the ground surface is suggested for the evaluation of the instability of a GPR system in field in the future.

An algorithm for automatic localization and detection of rebars from GPR data of concrete bridge decks

Abstract Picking rebars manually in the data from ground penetrating radar (GPR) surveys of concrete bridge decks is time consuming and labor intensive. This paper presents an automated rebar localization and detection algorithm for performing this task. The proposed methodology is based on the integration of conventional image processing techniques and deep convolutional neural networks (CNN). In the first step, the image processing methods, such as the migration, normalized cross correlation and thresholding, are used to localize pixels containing potential rebar peaks. In the second step, windowed images surrounding the potential pixels are first extracted from the raw GPR scans involved in the first step. Those are then classified by a trained CNN. In the process, likely true rebar peaks are recognized and retained, whereas likely false positive detections are discarded. The implementation of the proposed system in the analysis of GPR data for twenty-six bridge decks has shown excellent performance. In all cases, the accuracy of the proposed system has been greater than 95.75%. The overall accuracy for the entire deck library was found to be 99.60% ± 0.85%.

Method for attenuation assessment of GPR data from concrete bridge decks

Ground penetrating radar (GPR) is a well-accepted technology for condition assessment of concrete bridge decks. Such assessment has been mainly based on the measurement of attenuation of a signal reflected from the top rebar mat. Recently, a new approach for GPR data interpretation has been proposed, which is based on the correlation analysis of time-series GPR data. Motivated by that same research, the current paper presents an alternative method for performing the GPR attenuation analysis. In this method, instead of requiring time-series or baseline data, semi-simulated waveforms are developed and employed in a correlation analysis. With only one reflection retained from direct coupling, these waveforms mimic A-scans collected on a completely deteriorated bridge deck. The obtained results are then plotted in a form of contour maps of correlation coefficients, in which a higher value coefficient indicates more deteriorated concrete. The method was validated through its implementation on three bare concrete bridge decks. The condition maps from the proposed GPR correlation analysis correlate well to those obtained using the conventional GPR amplitude approach, and condition maps from several other nondestructive evaluation (NDE) techniques. However, in comparison to the conventional amplitude analysis, the proposed method provides a better description of the overall deterioration of bridge decks.

Time-frequency analysis of air-coupled GPR data for identification of delamination between pavement layers

Identification of delamination in pavement layers using ground penetrating radar (GPR) is still challenging due to its limited range resolution. This paper investigates the characteristics of the composite reflection from the air-filled delamination between pavement layers by time-frequency analysis. We firstly simulated GPR data from an asphalt pavement model with an embedded air gap of different thicknesses by the Green’s function method. Then we conducted a laboratory experiment on a delaminated asphalt pavement model. Both the numerical and laboratory experiment results demonstrate that both the peak instantaneous frequency and its amplitude are sensitive to the variation of the air gap thickness. When the thickness of the air gap is smaller than a quarter of the dominant wavelength, the peak instantaneous frequency of the composite reflection is higher than that of the normal interface reflection. We conclude that we can identify the delamination from the overall rise in the peak instantaneous frequency.

An Entropy-Based Analysis of GPR Data for the Assessment of Railway Ballast Conditions

The effective monitoring of ballasted railway track beds is fundamental for maintaining safe operational conditions of railways and lowering maintenance costs. Railway ballast can be damaged over time by the breakdown of aggregates or by the upward migration of fine clay particles from the foundation, along with capillary water. This may cause critical track settlements. To that effect, early stage detection of fouling is of paramount importance. Within this context, ground penetrating radar (GPR) is a rapid nondestructive testing technique, which is being increasingly used for the assessment and health monitoring of railway track substructures. In this paper, we propose a novel and efficient signal processing approach based on entropy analysis, which was applied to GPR data for the assessment of the railway ballast conditions and the detection of fouling. In order to recreate a real-life scenario within the context of railway structures, four different ballast/pollutant mixes were introduced, ranging from clean to highly fouled ballast. GPR systems equipped with two different antennas, ground-coupled (600 and 1600 MHz) and air-coupled (1000 and 2000 MHz), were used for testing purposes. The proposed methodology aims at rapidly identifying distinctive areas of interest related to fouling, thereby lowering significantly the amount of data to be processed and the time required for specialist data processing. Prominent information on the use of suitable frequencies of investigation from the investigated set, as well as the relevant probability values of detection and false alarm, is provided.

Concrete pavements curing evaluation with non-destructive tests

This study was completed by the Texas A&M Transportation Institute (TTI). The ground penetrating radar (GPR) technology and percometer were implemented for newly constructed highways. The GPR identifies the subsurface condition, which permits the user to determine the moisture availability for potential concrete curing. For this purpose, a GPR data acquisition program and data analysis system were developed by utilizing antenna. A combination of GPR information evaluation and curing quality evaluation is performed to diagnose the effectiveness of the applied curing compounds in terms of the moisture retention capability. Dielectric constant (DC) measurements were also taken on concrete specimens to indicate the free moisture content of the surface concrete. The new procedure consists of using measured relative humidity and temperature to calculate an Effectiveness Index (EI). EI and DC measurements indicate potentials to differentiate the curing quality of rigid pavement construction. Researchers examined the relationship between the Non-Destructive Testing (NDT) data and the actual concrete properties to develop “acceptability of quality” limits based upon the NDT data. The field investigations were conducted on two continuously reinforced concrete paving (CRCP) projects’ microfiber and internal curing mixtures.

A spectral analysis of ground-penetrating radar data for the assessment of the railway ballast geometric properties

This paper presents a methodology for the assessment of railway ballast using ground-penetrating radar (GPR – 2 GHz horn antenna). The primary approach in this endeavour was the finite-difference time-domain (FDTD) simulations of ballast (a multi-stage process in terms of ballast size). To this effect, a combination of random sequential adsorption (RSA) and FDTD algorithms were applied. The results of the numerical simulation then were used to compare with the experimental investigations results using a container (methacrylate material) of the 1.5 × 1.5 × 0.5 m dimensions. Finally, the modelling of the frequency spectrum peak and the equivalent diameter of the ballast aggregates was developed.

Gas bubble size estimation in peat soils from EM wave scattering observed with ground penetrating radar

AbstractThe size of biogenic gas bubbles in peatlands is believed to regulate ebullition of carbon gases to the atmosphere. The measurement of electromagnetic (EM) wave travel times using ground penetrating radar (GPR) is a proven field‐scale method for indirect estimation of volumetric gas content. However, there is also the possibility that information on the size of the gas bubbles can be determined from the analysis of the spectral content of GPR signals as scattering attenuation possesses a frequency dependence for bubbles smaller than the EM wavelength (Rayleigh‐type scattering). Theoretical modeling shows that GPR data acquired with typical antenna frequencies are likely to be affected by bubble size in peat soils. Analysis of GPR data from two recent studies on peat monoliths where biogenic gas production was documented produced results consistent with the model predictions. Using the approach, zero offset cross‐borehole GPR data in a northern peatland suggest that large bubble clusters (i.e., 0.05 m radius) occur in peat. These findings broaden the utility of GPR for providing information on biogenic gas dynamics in peatlands.

Corrosiveness mapping of bridge decks using image-based analysis of GPR data

Abstract Ground Penetrating Radar (GPR), a locating instrument by design, has attracted much interest as a non-destructive inspection technique for bridge decks due to its ease of use and ability to detect corrosion. The most commonly used technique to interpret GPR data is numerical analysis. The assessment method relies on the fact that corroded reinforcing bars, which cause signal attenuation, can be easily identified using GPR scans. However, several other unrelated factors can attenuate GPR signals such as reinforcing bar depth, surface anomalies and reinforcing bar spacing. These anomalies can be falsely interpreted as deterioration using numerical analysis. Image-based analysis overcomes these drawbacks through analyzing the entire GPR profile while considering prior knowledge of the structure characteristics, thus determining the state of bridge deck. The main objective of this research is to develop a systematic framework of the image-based analysis. The framework is supported by various GPR profiles depicting several causes of signal attenuation and their analysis with respect to deterioration or rebar corrosion status. Two case studies are presented and analyzed using numerical analysis, image-based analysis, and other Non-Destructive Evaluation (NDE) techniques. The results are compared to confirm the validity of the proposed methodology. Further validation is done using concrete cores. The developed approach is believed to assist transportation agencies in a more informed decision making process through highlighting areas of actual deterioration.

New Ground-Penetrating Radar Method Shows Promise in Aquifer

Recent advances in ground-penetrating radar data analysis could help reveal aquifer structure in unprecedented detail.

Cable Effects in Ground-Penetrating Radar Data and Implications for Quantitative Amplitude Measurements

Conductive cables have always represented a source of noise in ground-penetrating radar (GPR) data. In some instances, commercially available GPR systems use data processing tools to reduce cable noise. Such processes seldom respect the amplitude fidelity of the signal. For the purpose of careful, quantitative amplitude measurements, use of the raw recorded data is a critical starting point for reliable interpretation of results. During subsequent processing, users can compensate for cable effects to varying degrees. To illustrate the issues inherent with cable noise, we show an example where cable movement during data acquisition generates deviations in reflection amplitude up to 19%. We then present the ramifications of these variations for quantitative data analysis. We conclude that precise cable handling can improve data quality and subsequent data interpretation. Our results are particularly pertinent for quantitative analysis and inversion of GPR data where precise amplitude information is crucial.

Can a simple Numerical Model Help to Fine-Tune the Analysis of Ground-Penetrating Radar Data? Hochebenkar Rock Glacier as a Case Study

ABSTRACTLittle is known about the thickness of active Alpine rock glaciers, yet they are important components of the local hydrology. We use GPR data to determine the depth of the bedrock of Äußeres Hochebenkar rock glacier (Austria). There is no detailed information available regarding density and composition of the rock glacier, and assumptions about the signal propagation velocity have to be made when processing the GPR data. We use a simple creep model based on surface displacement and slope to calculate the thickness of the rock glacier along a flow line. We calculated bedrock profiles along the flow line for three different time periods, using input from multitemporal digital elevation models. We improved the fit of the profiles by calibrating the values used for layer densities and considered the model valid where the modelled bedrock profiles are within error of each other. We then compared the modeled values with the GPR data to check whether our assumptions for the propagation velocity produced results that match the model. While the fit is good at the lower end of the rock glacier, the GPR data appear to overestimate depth in the upper region. We adjusted the propagation velocity accordingly and find maximum thicknesses of over 50 m and a mean thickness of 30–40 m. The insights gained from the modeling approach thereby improved the fine-tuning of the GPR analysis.

Evaluating the Correlation Between the Geotechnical Index and the Electromagnetic Properties of Fouled Ballasted Track by a Full-Scale Laboratory Model

To determine the correlation between water content or fouling of a railroad track and ground-penetrating radar (GPR) signals, a full-scale railway track model was designed and constructed at the University of Massachusetts Amherst. A track section was simulated by creating a model consisting of rails and ties placed on a ballast layer on a subballast layer. The model was constructed three times with three fouling percentages. Each model was tested with water-content conditions of dry, field capacity, and two points in between these extremes. Frequency antennae of 450 MHz and 2 GHz were used to evaluate the conditions. The design and construction of the full-scale track in addition to the GPR data analysis and interpretation are presented in this paper. The results show that the dielectric permittivity and frequency spectrum can be used as an indicator of percentage of fouling and water content of a track. In addition, a linear correlation was observed between the percentage of fouling and the water content under field capacity conditions.

Impact of Data Processing and Antenna Frequency on Spatial Structure Modelling of GPR Data.

Over the last few years high-resolution geophysical techniques, in particular ground-penetrating radar (GPR), have been used in agricultural applications for assessing soil water content variation in a non-invasive way. However, the wide use of GPR is greatly limited by the data processing complexity. In this paper, a quantitative analysis of GPR data is proposed. The data were collected with 250, 600 and 1600 MHz antennas in a gravelly soil located in south-eastern Italy. The objectives were: (1) to investigate the impact of data processing on radar signals; (2) to select a quick, efficient and error-effective data processing for detecting subsurface features; (3) to examine the response of GPR as a function of operating frequency, by using statistical and geostatistical techniques. Six data processing sequences with an increasing level of complexity were applied. The results showed that the type and range of spatial structures of GPR data did not depend on data processing at a given frequency. It was also evident that the noise tended to decrease with the complexity of processing, then the most error-effective procedure was selected. The results highlight the critical importance of the antenna frequency and of the spatial scale of soil/subsoil processes being investigated.

Advances in GPR data acquisition and analysis for archaeology

The primary objective of this study is to evaluate the applicability and the effectiveness of ground-penetrating radar (GPR) to identify a thin burnt soil layer, buried more than 2 m below the topographic surface at the Liangzhu Site, in Southeastern China. The site was chosen for its relatively challenging conditions of GPR techniques due to electrical conductivity and to the presence of peach tree roots that produced scattering. We completed the data acquisition by using 100 and 200MHz antennas in TE and TM broadside and cross-polarized configurations. In the data processing and interpretation phase, we used GPR attribute analysis, including instantaneous phase and geometrical attributes. Validation analysis ground-truthing performed after the geophysical surveys, validated the GPR imaging, confirmed the electrical conductivity and relative dielectric permittivity (RDP) measurements performed at different depths, and allowed a reliable quantitative correlation between GPR results and subsurface physical properties. The research demonstrates that multiple antenna configurations in GPR data acquisition combined with attribute analysis can enhance the ability to characterize prehistoric archaeological remains even in complex subsurface conditions.