Ground Penetrating Radar Array Research Articles

Estimating the diameter of reinforcing bars using an ultra-wideband MIMO GPR array

Ground-penetrating radar (GPR) is an effective non-destructive detection technology for locating and characterizing reinforcing bars in concrete structures. However, the accurate quantification of reinforcing bar diameters, especially in small-diameter cases, remains a challenging issue. In this paper, a sizing method based on multiple-input-multiple-output (MIMO) GPR arrays is presented to estimate the reinforcing bar diameter in concrete. The method employs a linear array of ultra-wideband (UWB) antennas to acquire the full-matrix MIMO data of the reinforcing bar embedded in concrete. The diffraction stacking algorithm is applied to the obtained MIMO data to reconstruct the reinforcing bar. The 3 decibels (dB) drop technique is used to measure the chord length that passes through the peak intensity point of the reconstruction image of the reinforcing bar. Following that, the diameter of the reinforcing bar can be determined based on its cover depth and the chord length. Extensive numerical studies and experiments have been conducted to examine the performance of the proposed method in different scenarios. The method shows excellent sizing accuracy for reinforcing bars with different diameters and cover depths.

Continuous Automatic Estimation of Volumetric Water Content Profile During Infiltration Using Sparse Multi-Offset GPR Data

Ground-penetrating radar (GPR) is a non-destructive and non-invasive geophysical survey method that has been used to characterize soil volumetric water content (VWC) dynamics. An array antenna GPR system was used to collect nearly seamless, time-lapse multi-offset GPR data during an in-situ infiltration test on sand dunes with limited traces. Because the data volume was significant, an approach was utilized to automatically determine electromagnetic wave velocities from sparse common midpoint (CMP) data using standard velocity analysis, such as semblance analysis. The objective of this study was to develop a methodology that allows one to automatically perform velocity analysis by interpolating sparse CMP data obtained with the array GPR system. The proposed method determined the optimal normal moveout velocity values and the removal range of the F-K zone pass filter that minimized errors between the original and interpolated CMP data using leave-one-out cross-validation (LOOCV). After interpolating the sparse CMP data with the F-K zone pass filter, semblance analysis was used to determine the time-lapse velocity structure of the soil profile during water infiltration. The velocity data were converted to VWC data based on the Topp equation, which relates the soil VWC to the soil dielectric constant. The proposed method was tested using CMP data obtained via numerical simulation and experiments. The VWC profile from the proposed approach matched well with the independently observed VWC profiles obtained from an invasive probe-type soil moisture sensor.

Numerical modeling and data signal analysis of GPR array based on dual-field domain-decomposition time-domain finite element method

Traditional ground-penetrating radar (GPR) systems typically use a single transceiver antenna unit, which is challenging to achieve high-fidelity, ultra-narrow pulse transmission. It leads to problems such as limited detection resolution and insufficient data acquisition. This paper proposes a multi-polarization GPR array that uses multiple antenna elements to work synergistically. An electromagnetic field solving algorithm that enables parallel computation is introduced the time-domain finite element method of dual-field decomposition to achieve efficient and wideband simulation of the electromagnetic characteristics of large arrays. Each antenna element of the array system is treated as a subdomain during the solution process, and the electric and magnetic field values for each subdomain are calculated separately. Adjacent antenna elements are explicitly connected by equivalent surface currents on the interface of the subdomains. Through the method, numerically simulates the antenna array, establishes the spatial multi-polarization input signal, and analyzes the polarization response of the ground-penetrating radar (GPR) electromagnetic signal under the antenna array structure to the target body. The research results demonstrate that under the ground-penetrating radar array observation mode, the target's multi-polarization signal information can accurately and effectively reflect it's corresponding position and morphological relationship. The multi-polarized input signal can better compress the width of the wavelet and improve the range resolution of the target body. AAt the same time, the antenna array excites pulse signals with the same center frequency to be superimposed in the equivalent amplitude and same phase on space. The formed plane beam signal increases the radiation energy, improves the signal-to-noise ratio of the data, and eliminates the flicker caused by the radar cross-section changing with the observation angle, and weakens the influence of the discontinuity of the profile data in the horizontal direction caused by the antenna's unstable pattern and strengthens the data quality.

Electromagnetic energy focusing technology with GPR array transmitting antenna for high resolution detection

To accurately detect complex objects in urban underground space, an electromagnetic energy focusing technology is proposed in this paper with Ground penetrating radar (GPR) array transmitting antenna. The proposed GPR system with the four-element array synchronous excitation antenna is realized based on Wilkinson power divider, so as to improve the gain and directivity of antenna system. The simulation and measurement results have shown that the designed array GPR system has a bandwidth of 600 MHz ∼ 3 GHz, a maximum gain of 15 dBi and a half-power beam width of 32°. The gprMax forward simulation and sand trough experiment results have verified that the proposed system has obvious electromagnetic wave focusing effect, greater sounding and higher spatial resolution. It can provide technical support for non-destructive precise detection of urban shallow underground complex targets.

Research on application of ground penetrating radar array method based on plane beam signal in different geological models

The traditional common-offset ground penetrating radar method measures point by point along the survey line with a single transmitter and a single receiver. Due to the influence of the antenna radiation power and the low-pass filtering function of the earth medium, an intense amplitude gain cannot be obtained when the signal is intercepted. This article addresses a plane beam signal ground penetrating radar array observation method based on high radiation power gain. The transmitting antenna array simultaneously excites the pulse signal with the same centre frequency. All the transmitted signals interfere with each other at the near surface to form a plane beam signal, and the electromagnetic energy is superimposed mutually to increase the radiation power. We applied the plane beam signal ground penetrating radar array method to different geological models constructed by the finite difference time-domain (FDTD) algorithm for numerical simulation in this research. Since there are various offsets in the array ground penetrating radar observation method, we introduce a composite frequency shift-perfect matching layer (CFS-PML) based on the recursive convolution method as the absorbing boundary condition. It eliminates the problem of secondary reflection caused by the angle variation of the incident wave. The research result shows that the plane beam signal illuminates the target uniformly in space, can eliminate the discontinuity in profile data caused by the directivity of the antenna, improve the stability and quality of the echo signal, and enrich the target response parameters.

Clutter Distributions for Tomographic Image Standardization in Ground-Penetrating Radar

Multistatic ground-penetrating radar (GPR) signals can be imaged tomographically to produce three-dimensional distributions of image intensities. In the absence of objects of interest, these intensities can be considered to be estimates of clutter. These clutter intensities spatially vary over several orders of magnitude, and vary across different arrays, which makes direct comparison of these raw intensities difficult. However, by gathering statistics on these intensities and their spatial variation, a variety of metrics can be determined. In this study, the clutter distribution is found to fit better to a two-parameter Weibull distribution than Gaussian or lognormal distributions. Based upon the spatial variation of the two Weibull parameters, scale and shape, more information may be gleaned from these data. How well the GPR array is illuminating various parts of the ground, in depth and cross-track, may be determined from the spatial variation of the Weibull scale parameter, which may in turn be used to estimate an effective attenuation coefficient in the soil. The transition in depth from clutter-limited to noise-limited conditions (which is one possible definition of GPR penetration depth) can be estimated from the spatial variation of the Weibull shape parameter. Finally, the underlying clutter distributions also provide an opportunity to standardize image intensities to determine when a statistically significant deviation from background (clutter) has occurred, which is convenient for buried threat detection algorithm development which needs to be robust across multiple different arrays.

Experimental Research on the Pipe Grouting Quality Based on Antenna Array Radar

Experimental research on the pipe grouting quality is carried out by detecting the concrete test piece with high-frequency antenna array radar. First, the principle of detecting the pipe grouting quality with ground-penetrating radar is introduced, and then the pipe grouting situation is researched systematically and completely with three methods, including the oscillogram of a single wave, grey-scale image (2D imaging) and slice image (3D imaging) of antenna array radar, and the research results are verified with an indoor test model. The results show that: Pipe can be positioned precisely with antenna array ground-penetrating radar; for failure of judgment of the grouting fullness of metal pipes and the grouting fullness situation of non-metal pipes, the pipe grouting quality can be identified with the oscillogram of a single wave, grey-scale image (2D) and slice image (3D) respectively; Radar detection 3D image can present the position of a pipe in the structure intuitively and accurately, and, the pipe material and the pipe grouting fullness can be judged by comparing the radar detection 3D image and the 3D slice image.

Multi-Channel Ground-Penetrating Radar Array Surveys of the Iron Age and Medieval Ringfort Bårby on the Island of Öland, Sweden

As a part of the project “The Big Five”, large-scale multi-channel ground-penetrating radar surveys were carried out at Bårby ringfort (Swedish: borg), Öland, Sweden. The surveys were carried out using a MALÅ Imaging Radar Array (MIRA) system and aimed at mapping possible buried Iron Age and Medieval remains through the interior in order to better understand the purpose of the fort during its periods of use. An additional goal was to evaluate the impact of earlier farming on the preservation of the archaeological remains. The data provided clear evidence of well-preserved Iron Age and Medieval buildings inside the fort. The size and the pattern of the Iron Age houses suggest close similarities with, for example, the previously excavated fort at Eketorp on Öland. Given the presence of a substantial cultural layer together with a large number of artefacts recovered during a metal detection survey, it is suggested that Bårby borg’s primary function during the Iron Age was as a fortified village. The Medieval houses partly cover some of the Iron Age buildings. They are placed in a U-shape with an open square in the middle facing the edge of a limestone cliff. As in the case of Eketorp, it is suggested that the activities during Medieval times changed, but the precise purpose of the Medieval Bårby settlement is still a question open for debate. Future targeted archaeological investigations are needed in order to better understand its purpose. Rescue excavations may also be necessary, as the western steep cliff ledge is eroding and the well-preserved archaeological remains are at risk of being destroyed.

Development of Novel Methodology for Assessing Bridge Deck Conditions Using Step Frequency Antenna Array Ground Penetrating Radar

AbstractGround penetrating radar (GPR) has emerged during the last decade as a nondestructive testing method for assessing the subsurface condition of infrastructure components. However, the use of...

Archaeological Prospection with Motorised Multichannel Ground-Penetrating Radar Arrays on Snow-Covered Areas in Norway

The technical advancements of the past decade have rendered motorised, high-resolution ground-penetrating radar (GPR) investigations increasingly popular for archaeological research and cultural heritage management in Norway. However, the agricultural use of most survey areas limits the time available for fieldwork in spring and autumn and thus reduces the method’s potential. An extension of the fieldwork period into the winter season would be desirable. The project “Arkeologi i veien?” aimed to develop practical solutions for efficient motorised GPR surveys on snow and to evaluate to what extent the thickness of the snow cover affects data quality. Four sites with known archaeological remains in the ground have been investigated under snowless conditions and with snow cover. The comparative data analysis showed that GPR surveys can result in useful data even on areas covered with one metre of snow. This study shows that different temperatures and resulting variable snow conditions can have a strong effect on the quality of the generated GPR data. The possibility for GPR measurements on snow offers the opportunity to extend fieldwork into the winter period without conflicting with the growing season; however, local weather and snow conditions have to be closely observed in order to obtain useful prospection data.

Semi-automatic determination of layer depth, permittivity and moisture content for unbound granular pavements using multi-offset 3-D GPR

ABSTRACT A semi-automated multi-offset ground penetrating radar (GPR) analysis method called Ray-path Modelling Coherence (RM–C) was developed and field tested. It was used to quasi-continuously predict the depth, permittivity and volumetric moisture content of unbound granular (UBG) layers along a pavement site during two investigations using ground-coupled measurements from a 3-D GPR array. Predictions from the later site visit were compared to physical measurements of layer depth and moisture content at a number of locations along the site, which in general agreed well. RM-C permittivity predictions were compared to results from time domain reflectometery (TDR) sensors and diffraction hyperbola fitting of buried reflectors. The new approach reported higher permittivity values compared to these other methods, although showed similar trends in permittivity change with respect to pavement depth and ⁠variation over time. Reproducibility of the RM–C analysis was confirmed by comparing layer depth and moisture content predictions for repeat runs along the site, although occasional discrepancies were observed.

Velocity analysis of CMP gathers acquired by an array GPR system ‘Yakumo’: results from field application to tsunami deposits

This paper examines the capability of a multi-static ground penetrating radar (GPR) system ‘Yakumo’ to estimate a vertical profile of dielectric constants of stratified geological layers. Yakumo is equipped with eight transmitting and eight receiving antennas. By using Yakumo, we propose to obtain an eight-channel common mid-point (CMP) gather from the 64-channel multi-static radar dataset acquired at each point on the survey line. From each CMP gather, a vertical profile of interval velocities can be estimated by velocity spectrum analysis. By a laboratory sandbox experiment, we validate that the thickness of an 83 cm sand layer is estimated with an error of less than 4%. A field survey carried out on tsunami deposits demonstrates that our GPR method can provide the spatial distribution of layer velocities of the sedimentary structure and that the results are comparable with the geological logs at three points and a conventional common-offset GPR profile.

Practical Approach for High-Resolution Airport Pavement Inspection with the Yakumo Multistatic Array Ground-Penetrating Radar System.

It is important to identify the thin cracks within the airport pavement layers. To achieve this goal, a practical interferometric approach using the Yakumo multistatic ground-penetrating radar system was developed to detect the slight variability in wave propagation velocity and/or thickness caused by the thin cracks. In comparison with the conventional common midpoint (CMP) velocity estimation method, the proposed method can provide much higher-resolution estimations of slight deviations in the velocity and thickness from their corresponding reference values in the undamaged asphalt through the comparison of two CMP datasets. These deviations can be obtained analytically instead of graphically extracted from the CMP velocity spectrum. The proposed approach was not only analyzed using the simulated datasets, but also practically demonstrated at both an experimental model site and an actual airport site. In the simulation tests, velocity deviations on the order of a few millimeters per nanosecond were detected, and the experimental results shows good agreement with the ground truth and coring samples. This method provides a novel way to inspect partially damaged pavement when the thin cracks are difficult to detect using the reflected signals.

Tracking Infiltration Front Depth Using Time-lapse Multi-offset Gathers Collected with Array Antenna Ground Penetrating Radar.

A Ground Penetrating Radar (GPR) system based on a ground-coupled, densely populated antenna array was used to collect data during an infiltration experiment conducted at a test site near the Tottori Sand Dune, Japan. The antenna array used in this study consists of 10 transmitting antennas (Tx) and 11 receiving antennas (Rx). For this experiment, the system was configured to use all possible Tx-Rx pairings, resulting in a Multi-Offset Gather (MOG) consisting of 110 Tx-Rx combinations. The array was left stationary at a position directly above the infiltration area and data were collected every 1.5 seconds using a time-based trigger. Common-Offset Gather (COG) and Common Mid-Point (CMP) data cubes were reconstructed from the MOG data during post-processing. There have been few studies that used time-lapse CMP data to estimate changes in velocity of propagation. In this study, electromagnetic (EM) wave velocity was estimated heuristically at 1-minute intervals from the reconstructed CMP data through curve fitting, using the hyperbola equation. We then proceeded to calculate the depth of the wetting front. The evolution of the wetting front over time obtain through this method is consistent with the observations from a soil moisture sensor which was placed at a depth below 20 cm. The results obtained in this study demonstrate the ability of such array GPR system to monitor a subsurface dynamic process like water infiltration accurately and quantitatively.

Tracking Infiltration Front Depth Using Time-lapse Multi-offset Gathers Collected with Array Antenna Ground Penetrating Radar

A Ground Penetrating Radar (GPR) system based on a ground-coupled, densely populated antenna array was used to collect data during an infiltration experiment conducted at a test site near the Tottori Sand Dune, Japan. The antenna array used in this study consists of 10 transmitting antennas (Tx) and 11 receiving antennas (Rx). For this experiment, the system was configured to use all possible Tx-Rx pairings, resulting in a Multi-Offset Gather (MOG) consisting of 110 Tx-Rx combinations. The array was left stationary at a position directly above the infiltration area and data were collected every 1.5 seconds using a time-based trigger. Common-Offset Gather (COG) and Common Mid-Point (CMP) data cubes were reconstructed from the MOG data during post-processing. There have been few studies that used time-lapse CMP data to estimate changes in velocity of propagation. In this study, electromagnetic (EM) wave velocity was estimated heuristically at 1-minute intervals from the reconstructed CMP data through curve fitting, using the hyperbola equation. We then proceeded to calculate the depth of the wetting front. The evolution of the wetting front over time obtain through this method is consistent with the observations from a soil moisture sensor which was placed at a depth below 20 cm. The results obtained in this study demonstrate the ability of such array GPR system to monitor a subsurface dynamic process like water infiltration accurately and quantitatively.

Monitoring Infiltration Process Seamlessly Using Array Ground Penetrating Radar

Core Ideas Array GPR can be used to monitor infiltration into sand dune seamlessly. Array GPR enables sequentially acquired multi‐offset gather data. Array GPR data agree well with data measured independently with soil moisture sensors. Because an array ground penetrating radar (GPR) electrically switches any antenna combinations sequentially in milliseconds, both common‐offset gather (COG) and multi‐offset gather (MOG) data can be acquired almost seamlessly. The main objective of this study was therefore to determine if COG and MOG surveys by array GPR, which allows 110 different antenna combinations, could detect a wetting front during vertical field infiltration. An infiltration experiment was conducted in an experimental field inside Tottori Sand Dune, Japan. Time‐lapse radargrams of COG and MOG by array GPR clearly show the wetting front evolution with time. Reflection signals in MOG radargrams agree well with two‐way travel times predicted from dielectric constant observed independently with a soil moisture sensor. This study confirms the usefulness of array GPR for monitoring and quantifying the infiltration process in the field.

Near range radar and its application to near surface geophysics and disaster mitigation

In this paper, we discuss about the near range radar applied to various environmental applications and disaster mitigation issues. Synthetic aperture radar (SAR) processing or migration is the key technology in near range radar imaging, which can be used in ground penetrating radar (GPR) and ground-based synthetic aperture radar (GB-SAR). We demonstrate some applications which include GPR for humanitarian demining, GPR for archaeological survey, GB-SAR for landslide monitoring and nondestructive inspection of wooden buildings. We also demonstrate a new array GPR system “Yakumo”, which was used for archaeological survey for demonstration of advanced multi-static radar signal processing for better radar imaging.

Step‐frequency ground‐penetrating‐radar array calibration requirements to estimate dielectric properties of pavements

ABSTRACTDuring the past decade, ground penetrating radar has emerged as a viable non‐destructive testing technology for quality control and quality assurance during pavement construction and for the infrastructure subsurface condition assessment. Data are collected with the ground penetrating radar antenna array attached to a vehicle travelling along the road. With ground penetrating radar data, there is a corresponding need to follow strict protocols both in data collection and data processing, especially for antenna arrays. The key to successful data measurements is the application of calibra‐tion procedures appropriate to the hardware system, measurement protocols, and desired measurement statistic or parameter. This paper presents four primary calibration procedures required for ground penetrating radar antenna arrays with actual case application using an air‐coupled step‐frequency ground penetrating radar array. These calibration procedures for a step‐frequency ground penetrating radar antenna array are applied to produce the ground penetrating radar signal foundation for estimating the dielectric properties of materials in a layered highway pavement structure. In addition, a complete solution space is required to identify all layer interfaces and buried objects.

New evidence for a Roman military camp at Virunum (Noricum): Th e garrison of the governor’s guard (singulares)?

Since the year 2001, aerial photographs have indicated a densely built-up zone to the east of the Roman town of Virunum (near Klagenfurt, Carinthia, Austria), the capital of the province of Noricum. The visible crop marks have been interpreted as a Roman military camp. The Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology (LBI ArchPro) conducted an initial ground penetrating radar survey on November 19, 2013, in order to gather further information regarding the close proximity of a military installation to the civilian town. An area of 2.56 ha was surveyed using a motorized high resolution MIRA ground penetrating radar array from Malå Geoscience. In the northern part of the plot, numerous building structures are visible, obviously from Roman times, which were situated within a walled-in area. A gateway was located on the south side of this enclosed zone. The forested western and northern sides of this enclosure seem to coincide with the modern land division. Three long rectangular structures, which appear to be Roman military barracks with double chambers and so-called “Kopfbauten” (habitation area for the officers), are a key for the interpretation of the entire complex. Another densely occupied area is located to the south of the enclosure and was probably inhabited by civilians. These new GPR data clearly provides novel insights in the manner Roman troops were housed at the governor’s seat of Noricum.

Mechatronic Systems Design for an Autonomous Robotic System for High-Efficiency Bridge Deck Inspection and Evaluation

The condition of bridges is critical for the safety of the traveling public. Bridges deteriorate with time as a result of material aging, excessive loading, environmental effects, and inadequate maintenance. The current practice of nondestructive evaluation (NDE) of bridge decks cannot meet the increasing demands for highly efficient, cost-effective, and safety-guaranteed inspection and evaluation. In this paper, a mechatronic systems design for an autonomous robotic system for highly efficient bridge deck inspection and evaluation is presented. An autonomous holonomic mobile robot is used as a platform to carry various NDE sensing systems for simultaneous and fast data collection. The robot's NDE sensor suite includes ground penetrating radar arrays, acoustic/seismic arrays, electrical resistivity sensors, and video cameras. Besides the NDE sensors, the robot is also equipped with various onboard navigation sensors such as global positioning system (GPS), inertial measurement units (IMU), laser scanner, etc. An integration scheme is presented to fuse the measurements from the GPS, the IMU and the wheel encoders for high-accuracy robot localization. The performance of the robotic NDE system development is demonstrated through extensive testing experiments and field deployments.