An overview of ground-penetrating radar signal processing techniques for road inspections
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paper_title: Incorporating Road Safety into Pavement Management

paper_content:

Improving road safety through proper pavement engineering and maintenance should be one of the major objectives of pavement management systems. When pavements are evaluated in terms of safety, a number of factors related to pavement engineering properties are raised, such as pavement geometric design, paving materials and mix design, pavement surface properties, shoulder type, and pavement color and visibility. Each year there are voluminous annual reports on traffic accident statistics and discussions of such road safety issues as road safety modeling and pavement safety measurements and criteria. Although road safety may be considered a separate area, it should be incorporated into pavement management systems. The main pavement engineering relationships associated with road safety are identified, and the various aspects of road safety related to pavement management, such as pavement types, pavement surface macrotexture and microtexture, and pavement safety measurements, criteria, and evaluation methods, are discussed. A systematic approach is proposed for the coordination of pavement maintenance programs with road safety improvement and the incorporation or integration of safety management with pavement and other management systems. Finally, a list of possible remedial measures for road safety improvements associated with pavement maintenance activities is recommended.
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paper_title: Improving safety of runway overrun through the correct numerical evaluation of rutting in cleared and graded areas

paper_content:

Aircraft overrun is potentially very dangerous to human life. Statistics show that overrun is mainly due to human errors causing loss of control in wheel alignment, high approach speed, and long touchdown. To prevent such disastrous consequences, advanced material arresting systems are currently being used in the main international airports for construction of Runway Safety Areas (RSAs). Many predictive models have been developed for controlling overrun events: the early reliable numerical models, on the basis of theoretical streamlined assumptions, were gradually replaced. More rigorous models based on Multibody System (MBS) and Finite Element Method (FEM) theories are nowadays much more preferred. These are characterized by high levels of reliability, even though the large number of data required does not always allow an exhaustive description of the domain of analysis. The paper presents an alternative method for predicting rut depths induced by aircraft overrunning. Such method is based on a numerical streamlined model, integrated with measurements from Light Falling Weight Deflectometer (LFWD), to define, section by section, the mechanical properties of soils in Cleared and Graded Areas (CGAs). The method has been validated through in situ tests, showing its high effectiveness and efficiency.
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paper_title: Road evaluation with ground penetrating radar

paper_content:

This paper provides a status report of the Ground Penetrating Radar (GPR) highway applications based on studies conducted in both Scandinavia and the USA. After several years of research local transportation agencies are now beginning to implement GPR technology for both network and project level surveys. This paper summarizes the principles of operation of both ground-coupled and air-launched GPR systems together with a discussion of both signal processing and data interpretation techniques. In the area of subgrade soil evaluation GPR techniques have been used to nondestructively identify soil type, to estimate the thickness of overburden and to evaluate the compressibility and frost susceptibility of subgrade soil. In road structure surveys, GPR has been used to measure layer thickness, to detect subsurface defects and to evaluate base course quality. In quality control surveys, GPR techniques have been used for thickness measurements, to estimate air void content of asphalt surfaces and to detect mix segregation. Future developments are described where the technique has great potential in assisting pavement engineers with their new pavement designs and in determining the optimal repair strategies for deteriorated roadways.
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paper_title: Novel perspectives in bridges inspection using GPR

paper_content:

Bridge engineers increasingly prefer to use the Ground-Penetrating Radar (GPR) technique. GPR can yield data with very high spatial resolution, the data can be acquired rapidly and even during traffic, causing very low interferences. This paper presents a novel GPR system that is designed and developed for bridge applications. In addition it proposes a new algorithm for cracks tracking in a three-dimensional domain. The effectiveness and accuracy of the procedure have been calibrated and validated on four different bridges. In this paper, three-dimensional visualisations of cracks and two-dimensional tomographies and sections are shown to demonstrate the potentialities of the GPR system associated to the signal-processing algorithm.
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paper_title: Surface and borehole ground-penetrating-radar developments

paper_content:

During the past 80 years, ground-penetrating radar (GPR) has evolved from a skeptically received glacier sounder to a full multicomponent 3D volume-imaging and characterization device. The tool can be calibrated to allow for quantitative estimates of physical properties such as water content. Because of its high resolution, GPR is a valuable tool for quantifying subsurface heterogeneity, and its ability to see nonmetallic and metallic objects makes it a useful mapping tool to detect, localize, and characterize buried objects. No tool solves all problems; so to determine whether GPR is appropriate for a given problem, studying the reasons for failure can provide an understanding of the basics, which in turn can help determine whether GPR is appropriate for a given problem. We discuss the specific aspects of borehole radar and describe recent developments to become more sensitiveto orientation and to exploit the supplementary information in different components in polarimetric uses of radar data. Multicomponent GPR data contain more diverse geometric information than single-channel data, and this is exploited in developed dedicated imaging algorithms. The evolution of these imaging schemes is discussed for ground-coupled and air-coupled antennas. For air-coupled antennas, the measured radiated wavefield can be used as the basis for the wavefield extrapolator in linear-inversion schemes with an imaging condition, which eliminates the source-time function and corrects for the measured radiation pattern. A handheld GPR system coupled with a metal detector is ready for routine use in mine fields. Recent advances in modeling, tomography, and full-waveform inversion, as well as Green's function extraction through correlation and deconvolution, show much promise in this field.
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paper_title: FDTD simulation of the GPR signal for effective inspection of pavement damages

paper_content:

Ground-penetrating radar (GPR) is a wide ranging non-destructive tool used in many fields of application including effective pavement engineering surveys. Despite the high potential and the consolidated results obtained over the past decades, pavement distress manuals based on visual inspections are still widely used, so that only the effects and not the causes of faults are generally considered. In such context, simulation can represent an effective solution for supporting engineers and decision-makers in understanding the deep responses of both revealed and unrevealed damages. In this study, the use of FDTD simulation of the GPR signal is analyzed by simulating three different types of flexible pavement at two different center frequencies of investigation commonly used for road surveys. Comparisons with the undisturbed modelled pavement sections are carried out showing promising agreements with theoretical expectations, and good chances for detecting the shape of damages are demonstrated.
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paper_title: Inferring bearing ratio of unbound materials from dielectric properties using GPR: The case of runaway safety areas

paper_content:

In this paper, the correlation between the dielectric and the strength properties of unbound materials is analyzed, considering that mechanical characteristics of soil depend on particle interactions and assuming that dielectric properties of materials are related to bulk density. The work investigates this topic using ground-penetrating radar (GPR) techniques. In particular, two ground-coupled GPR are used in laboratory and in field experiments to infer the bearing ratio of soil in runway safety areas (RSA). The procedure is validated through CBR tests and in situ measurements using the light falling weight deflectometer (LFWD). A promising empirical relationship between the relative electric permittivity and the resilient modulus of soils is found. The comparison between measured and predicted data shows a reliable prediction of Young's modulus, laying the foundation for inferring mechanical properties of unbound materials through GPR measurements.
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paper_title: Large-scale analysis of dielectric and mechanical properties of pavement using GPR and LFWD

paper_content:

Over the last few years ground-penetrating radar (GPR) has proved to be an effective instrument for pavement applications spanning from physical to geometrical inspections of roads. In this paper, the new challenge of inferring mechanical properties of road pavements and materials from their dielectric characteristics was investigated. A pulsed GPR system with ground-coupled antennas, 600 MHz and 1600 MHz center frequencies of investigation, was used over a 4 m×30 m test site with a flexible pavement structure. A spacing of 0.40 m between the GPR acquisition tracks was considered both longitudinally and transversely in order to configure a square regular grid mesh of 836 nodes. Accordingly, the Young's modulus of elasticity was measured on each grid node using light falling weight deflectometer (LFWD). Therefore, a semi-empirical model for predicting strength properties of pavement was developed by comparing the observed elastic modulus and the electromagnetic response of substructure on each grid node. A good agreement between observed and modeled values was found, thereby showing great promises for large-scale mechanical inspections of pavements using GPR.
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paper_title: Accuracy of pavement thicknesses estimation using different ground penetrating radar analysis approaches

paper_content:

The Ground Penetrating Radar (GPR) is a Non-destructive Testing (NDT) technique, which is able to capture continuous pavement layer thicknesses data. The radar pulse propagation is a major factor for gathering the dielectric constants of pavement materials accurately. The present research focuses on the accuracy of pavement asphalt layer thicknesses estimation using GPR data analysis by employing different estimation approaches based on material dielectric properties. A comprehensive comparative analysis of GPR and asphalt-drilled cores data incorporating a variety of pavements is performed. The major findings of the detailed comparative analysis including the effectiveness of the approaches used are reported and discussed in the present paper.
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paper_title: APPROACH TO DETERMINING IN SITU DIELECTRIC CONSTANT OF PAVEMENTS: DEVELOPMENT AND IMPLEMENTATION AT INTERSTATE 81 IN VIRGINIA

paper_content:

A major problem in using ground penetrating radar (GPR) for estimating pavement layer thickness is assuming the dielectric properties of that layer. Pavement dielectric properties may vary significantly due to aggregate type, moisture presence, and other conditions. Therefore, uncertainties in the dielectric constant, which may vary from 3 to 15, will result in misleading thickness determination. Obtaining cores for calibration may reduce the error, but the variation in the dielectric constant along the roadway often leads to errors in the thickness determination. A method was developed to determine the dielectric constant, and therefore the thickness, of the hot-mix asphalt (HMA) layer of a pavement using GPR. Because of the different compositions and ages of the layers forming HMA in older pavements, dielectric constant estimation based on the surface reflection may not be accurate and may lead to wrong thickness estimations. The developed method uses a modified common midpoint technique (usually used i...
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paper_title: Step-frequency ground-penetrating-radar array calibration requirements to estimate dielectric properties of pavements

paper_content:

During 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 calibration ::: 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.
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paper_title: APPROACH TO DETERMINING IN SITU DIELECTRIC CONSTANT OF PAVEMENTS: DEVELOPMENT AND IMPLEMENTATION AT INTERSTATE 81 IN VIRGINIA

paper_content:

A major problem in using ground penetrating radar (GPR) for estimating pavement layer thickness is assuming the dielectric properties of that layer. Pavement dielectric properties may vary significantly due to aggregate type, moisture presence, and other conditions. Therefore, uncertainties in the dielectric constant, which may vary from 3 to 15, will result in misleading thickness determination. Obtaining cores for calibration may reduce the error, but the variation in the dielectric constant along the roadway often leads to errors in the thickness determination. A method was developed to determine the dielectric constant, and therefore the thickness, of the hot-mix asphalt (HMA) layer of a pavement using GPR. Because of the different compositions and ages of the layers forming HMA in older pavements, dielectric constant estimation based on the surface reflection may not be accurate and may lead to wrong thickness estimations. The developed method uses a modified common midpoint technique (usually used i...
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paper_title: Road evaluation with ground penetrating radar

paper_content:

This paper provides a status report of the Ground Penetrating Radar (GPR) highway applications based on studies conducted in both Scandinavia and the USA. After several years of research local transportation agencies are now beginning to implement GPR technology for both network and project level surveys. This paper summarizes the principles of operation of both ground-coupled and air-launched GPR systems together with a discussion of both signal processing and data interpretation techniques. In the area of subgrade soil evaluation GPR techniques have been used to nondestructively identify soil type, to estimate the thickness of overburden and to evaluate the compressibility and frost susceptibility of subgrade soil. In road structure surveys, GPR has been used to measure layer thickness, to detect subsurface defects and to evaluate base course quality. In quality control surveys, GPR techniques have been used for thickness measurements, to estimate air void content of asphalt surfaces and to detect mix segregation. Future developments are described where the technique has great potential in assisting pavement engineers with their new pavement designs and in determining the optimal repair strategies for deteriorated roadways.
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paper_title: Geophysical surveys of burial sites: A case study of the Oaro urupa

paper_content:

A Maori family burial site was surveyed using shallow electromagnetic (EM), magnetometer/gradiometer, and ground‐penetrating radar (GPR) techniques. The locations of some older graves are no longer known, partly through the loss of markers and partly through the loss of the oral record. There are at least 150 such burial sites throughout New Zealand, and similar problems occur elsewhere in the world. The knowledge that Maori graves are traditionally set out facing east made survey design easier. Background trends are removed, and possible anomalous features are identified, despite the complicating presence of metal fencing. The EM in‐phase response, the vertical gradient of the total magnetic field, and the GPR response were particularly useful in combination. GPR surveys were carried out using two frequencies: 450 and 200 MHz. The higher frequency radar surveys were limited in extent because these data had a limited depth of penetration and were prone to signal “ringing” in the surficial clay. The lower ...
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paper_title: Where is true time zero ?

paper_content:

The accurate setting of the zero time position relative to the ground surface is a parameter which concerns all GPR operators and it is an essential factor for conducting accurate shallow depth measurements in GPR. But where is the true ground surface on our radargrants? This paper examines the setting of the true zero time position. It presents the results of a survey defining where GPR users and equipment manufacturers currently set their zero time position. In field operations it is necessary to place the zero time at a clearly definable and stable location in the early wavelet. This is commonly at either the negative or positive maximum peaks of the first wavelet, or the zero amplitude point between these two peaks. This position needs to be corrected for in subsequent data processing in order to make accurate and reproducible depth or thickness measurements in materials. In reality the precisely calibrated true ground surface position in time is not where is it commonly thought to be located on the early time wavelet, due to the inherent characteristics of the signal generating electronics, the transmitting and receiving antennae and variations in the electrical properties of the investigated medium in close proximity to the antenna. An understanding of the near-field characteristics of a bowtie antenna, coupled with extensive comparisons via empirical observations from numerous coreholes, enables us to predict where the true zero time actually occurs in a pulse GPR system.
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paper_title: Processing Ground Penetrating Radar Data To Improve Resolution Of Near-Surface Targets

paper_content:

Although unprocessed ground penetrating radar (GPR) data are capable of producing detailed images of the shallow subsurface, these images may be difficult to interpret reliably. Here, we investigate characteristics of GPR signals and various techniques to enhance GPR images. The processing steps are tested on GPR datasets acquired at a well-controlled site where two concrete blocks, simulating archaeological structures, are buried less than two meters from the surface. Short range GPR signals often possess a low-frequency component (commonly referred to as a ttwowtt) that causes amplitude distortion along an individual trace. Characteristics of this noise are considered in light of its physical cause, i.e., saturation of the receiver electronics. Three filter techniques were tested to remove the wow: (i) residual mean filtering, (ii) bandpass filtering, and (iii) residual median filtering. We found that the residual median filter performed best. Additional signal processing steps included static corrections, normal moveout (NMO) corrections, migration and eigen filtering. Static corrections compensate for drift of the time-zero sample that occurs during acquisition. NM0 corrections remove spatial distortion due to source-receiver offset. Migration focuses diffracted energy and corrects dipping reflectors thereby improving spatial resolution. Eigen filtering removes the coherent direct arrivals to improve the detection of near-surface features. Application of these processing techniques significantly improves the quality of the GPR images from the test site, both in terms of the positioning of events and resolving capability. By testing various enhancement techniques on data collected at wellcontrolled sites, a better understanding is gained of their relative benefits and the ultimate capabilities of GPR as a shallow exploration tool.
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paper_title: Optimal mean-absolute-error filtering of gray-scale signals by the morphological hit-or-miss transform

paper_content:

The binary hit-or-miss transform is applied to filter digital gray-scale signals. This is accomplished by applying a union of hit-or-miss transforms to an observed signal's umbra and then taking the surface of the filtered umbra as the estimate of the ideal signal. The hit-or-miss union is constructed to provide the optimal mean-absolute-error filter for both the ideal signal and its umbra. The method is developed in detail for thinning hit-or-miss filters and applies at once to the dual thickening filters. It requires the output of the umbra filter to be an umbra, which in general is not true. A key aspect of the paper is the complete characterization of umbra-preserving union-of-hit-or-miss thinning and thickening filters. Taken together, the mean-absolute-error theory and the umbra-preservation characterization provide a full characterization of binary hit-or-miss filtering as applied to digital gray-scale signals. The theory is at once applicable to hit-or-miss filtering of digital gray-scale images through the three-dimensional (3-D) binary hit-or-miss transform.
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paper_title: Recognizing surface scattering in ground-penetrating radar data

paper_content:

Ground-penetrating radar (GPR) data may show strong noise events as a result of scattering by surface objects on the ground or above the survey line. The relative strength of these events can be large in comparison to reflections from geologic features, because radar signals in the ground attenuate exponentially whereas signals that travel in the air attenuate geometrically. Migration of GPR field data from clastic and carbonate sequences in central Oklahoma distinguishes between scattered events and geologic events because the former are focused at the air-wave velocity, while the latter are focused at the ground-wave velocity. Forward modeling using locations of scatterers derived from migration confirms the presence of scattered events, and common midpoint (CMP) gathers are helpful in identifying surface scattering. Scattered events displayed at a horizontal/vertical scale of 1:1 are easily mistaken for subhorizontal, geologic reflections. Methods of recognizing scattered events and removing them, if possible, are therefore crucial to correct geological interpretation of GPR data.
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paper_title: Spectral balancing GPR data using time-variant bandwidth in the t-f domain

paper_content:

Ground-penetrating radar (GPR) sections encounter a resolution reduction with depth because, for electromagnetic (EM) waves propagating in the subsurface, attenuation is typically more pronounced at higher frequencies. To correct for these effects, we have applied a spectral balancing technique, using the S-transform (ST). This signal-processing technique avoids the drawbacks of inverse Q* filtering techniques, namely, the need for estimation of the attenuation factor Q* from the GPR section and instability caused by scattering effects that result from methods of dominant frequency-dependent estimation of Q* . The method designs and applies a gain in the time-frequency ( t-f ) domain and involves the selection of a time-variant bandwidth to reduce high-frequency noise. This method requires a reference amplitude spectrum for spectral shaping. It performs spectral balancing, which works efficiently for GPR data when it is applied in very narrow time windows. Furthermore, we have found that spectral balancin...
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paper_title: Coherent noise attenuation in GPR data by linear and parabolic Radon Transform techniques

paper_content:

Ground Penetrating Radar (GPR) is a geophysical method increasingly used in numerous shallow applications. ::: Unfortunately, electronic or acquisition problems can cause the presence in the radargrams of coherent noise ::: interfering with the useful signal. A commonly observed phenomenon, especially for not-shielded antennae, is the ::: surface-scattering effect, due to reflection or diffraction from above-surface objects. These noise events appear ::: with a characteristic hyperbolic moveout in the usual common-offset sections. Other frequent problems are related ::: to the presence of horizontal or dipping features due to system-ringing or other non-geological causes. Several ::: methods have been tried to overcome these problems, most of which involve time domain or Fourier domain ::: filtering. This work presents an attempt to reduce some of these noise modes by an original adaptation of filtering ::: techniques implemented in the Radon domain. The Radon Transform (RT), both in the linear (or t-p) and in the ::: parabolic version (or t-q), has been widely used in seismic processing, especially for multiple removal, but is ::: still quite unfamiliar to GPR practitioners. The results achieved by different RT based methods for coherent noise ::: attenuation in a GPR field example, compared to those of more conventional techniques, are quite encouraging.
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paper_title: Location of Archaeological Structures using GPR Method: Three-dimensional Data Acquisition and Radar Signal Processing

paper_content:

Generally, in order to detect shallow archaeological features, such as tombs, cavities, walls, etc., ground penetrating radar (GPR) data are acquired along parallel profiles. In some cases, the data collected using the GPR method are difficult to interpret owing to the presence of low signal-to-noise (S/N) ratio. These signals can be generated by several factors that significantly influence the radar profiles. To enhance the interpretation of radar sections, three-dimensional data acquisition, radar signal processing and time-slice representation are used. ::: ::: ::: ::: The archaeological investigated as a test site was the Sabine Necropolis (700–300 BC) at Colle del Forno (Montelibretti, Roma), believed to contain unexplored underground dromos chamber tombs. The measurements were carried out along parallel profiles in a test area, using Sir System 10 (GSSI) equipped with different antennas operating at 100, 300 and 500 MHz. The spatial interval used during the survey was 20 cm. To enhance the S/N ratio, a band-pass filter and subtraction of an average trace on the field data has been applied; furthermore, the two-dimensional migration technique on all profiles collected was used in order to move diffraction effects. A time-slice representation technique was adopted to obtain a planimetric correlation between anomalous bodies at different depths. ::: ::: ::: ::: The results indicate that the three-dimensional data acquisition, processing and the time slice representation can help determine the location, depth and shapes of buried features.
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paper_title: Large-scale analysis of dielectric and mechanical properties of pavement using GPR and LFWD

paper_content:

Over the last few years ground-penetrating radar (GPR) has proved to be an effective instrument for pavement applications spanning from physical to geometrical inspections of roads. In this paper, the new challenge of inferring mechanical properties of road pavements and materials from their dielectric characteristics was investigated. A pulsed GPR system with ground-coupled antennas, 600 MHz and 1600 MHz center frequencies of investigation, was used over a 4 m×30 m test site with a flexible pavement structure. A spacing of 0.40 m between the GPR acquisition tracks was considered both longitudinally and transversely in order to configure a square regular grid mesh of 836 nodes. Accordingly, the Young's modulus of elasticity was measured on each grid node using light falling weight deflectometer (LFWD). Therefore, a semi-empirical model for predicting strength properties of pavement was developed by comparing the observed elastic modulus and the electromagnetic response of substructure on each grid node. A good agreement between observed and modeled values was found, thereby showing great promises for large-scale mechanical inspections of pavements using GPR.
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paper_title: Using Suction and Dielectric Measurements as Performance Indicators for Aggregate Base Materials

paper_content:

A simple laboratory test for evaluating unstabilized granular base material is introduced. The test consists of monitoring the capillary rise of moisture within a 300-mm-high cylinder of compacted aggregate. The moisture conditions at the aggregate surface are monitored with a dielectric probe. A graph of surface dielectric versus time is used as the basis for performance classification. The poorest-performing materials are those that rapidly reach saturation and exhibit high surface dielectric values. The dielectric is a measure of the “free” or unbound water within the aggregate sample. It is not a simple measure of the moisture content of the material but an assessment of the state of bonding of the water within the fine aggregates. It is this unbound water that is thought to be directly related to the strength of the material and to its ability to withstand repeated freeze-thaw cycling. This test was developed by the Finnish National Road Administration and successfully used to investigate a major fle...
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paper_title: Road evaluation with ground penetrating radar

paper_content:

This paper provides a status report of the Ground Penetrating Radar (GPR) highway applications based on studies conducted in both Scandinavia and the USA. After several years of research local transportation agencies are now beginning to implement GPR technology for both network and project level surveys. This paper summarizes the principles of operation of both ground-coupled and air-launched GPR systems together with a discussion of both signal processing and data interpretation techniques. In the area of subgrade soil evaluation GPR techniques have been used to nondestructively identify soil type, to estimate the thickness of overburden and to evaluate the compressibility and frost susceptibility of subgrade soil. In road structure surveys, GPR has been used to measure layer thickness, to detect subsurface defects and to evaluate base course quality. In quality control surveys, GPR techniques have been used for thickness measurements, to estimate air void content of asphalt surfaces and to detect mix segregation. Future developments are described where the technique has great potential in assisting pavement engineers with their new pavement designs and in determining the optimal repair strategies for deteriorated roadways.
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paper_title: Pavement Analysis and Design

paper_content:

This is a textbook on the structural analysis and design of highway pavements. It presents the theory of pavement design and reviews the methods developed by several organizations, such as the American Association of State Highway and Transportation Officials (AASHTO), the Asphalt Institute (AI), and the Portland Cement Association (PCA). It can be used for an undergraduate course by skipping the appendices or as an advanced graduate course by including them. The book is organized in 13 chapters. Chapter 1 introduces the historical development of pavement design, the major road tests, the various design factors, and the differences in design concepts among highway pavements, airport pavements, and railroad trackbeds. Chapter 2 discusses stresses and strains in flexible pavements. Chapter 3 presents the KENLAYER computer program, based on Burmister's layered theory, including theoretical developments, program description, comparison with available solutions, and sensitivity analysis on the effect of various factors on pavement responses. Chapter 4 discusses stresses and deflections in rigid pavements due to curling, loading, and friction, as well as the design of dowels and joints. Influence charts for determining stresses and deflections are also presented. Chapter 5 presents the KENSLABS computer program, based on the finite element method, including theoretical developments, program description, comparison with available solutions, and sensitivity analysis. Chapter 6 discusses the concept of equivalent single-wheel and single-axle loads and the prediction of traffic. Chapter 7 describes the material characterization for mechanistic-empirical methods of pavement design including the determination of resilient modulus, fatigue and permanent deformation properties, and the modulus of subgrade reaction. Chapter 8 outlines the subdrainage design including general principles, drainage materials, and design procedures. Chapter 9 discusses pavement performance including distress, serviceability, skid resistance, nondestructive testing, and the evaluation of pavement performance. Chapter 10 illustrates the reliability concept of pavement design in which the variabilities of traffic, material, and geometric parameters are all taken into consideration. A probabilistic procedure, developed by Rosenblueth, is described and two probabilistic computer programs including VESYS for flexible pavements and PMRPD for rigid pavements are discussed. Chapter 11 outlines an idealistic mechanistic method of flexible pavement design and presents in detail the AI method and the AASHTO method, as well as the design of flexible pavement shoulders. Chapter 12 outlines an idealistic mechanistic method of rigid pavement design and presents in detail the PCA method and the AASHTO method. The design of continuous reinforced concrete pavements and rigid pavement shoulders is also included. Chapter 13 outlines the design of overlay on both flexible and rigid pavements including the AASHTO, AI, and PCA procedures. An Author Index and a Subject Index are provided.
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paper_title: Support Vector Regression method applied to thin pavement thickness estimation by GPR

paper_content:

In the field of civil engineering, sounding the layers is classically performed using standard ground-penetrating radar (GPR), whose vertical resolution is bandwidth dependent. The layer thicknesses are deduced from both the time delays of backscattered echoes and the dielectric constants of the layers. In contrast with the conventional spectral analysis approaches, we propose in this paper to use one of the most powerful machine learning algorithm, namely the Support Vector Machine(SVM), to perform Time Delay Estimation (TDE) of backscattered radar signals. In particular, this paper demonstrates the super time resolution capability of such technique in the context of overlapping and totally correlated echoes when thin pavement layers survey is under scope.
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paper_title: Permittivity measurements of multilayered media with monostatic pulse radar

paper_content:

Electromagnetic (EM) inversion is a useful tool for quantitative analysis in short-range applications of pulse radars. To estimate multilayered media properties using monostatic radar, two inverse scattering approaches are discussed: (a) layer-stripping algorithm by exploiting amplitude and time delay of radar echoes after their detection, and (b) EM inverse problem of parameter optimization by minimizing the mean square error between measured and modeled data. Redundancy in the estimation of media properties is given by spatial continuous measurements of the investigated media. This property is exploited in both the approaches investigated. In the layer-stripping approach the medium within each layer is homogeneous and the interfaces are assumed laterally continuous. In the inverse problem permittivity is assumed to be laterally smooth, implicit smoothing being given in the model parameterization. It is implicit in both methods that the inversion accuracy is strictly related to the amplitude stability of the radar and plane wave approximation. Therefore, the system calibration and the compensation of some propagation effects (e.g., near field, losses due to conductivity and to scattering from particles distributed between layers and on interfaces, pulse distortion) become crucial aspects for each specific application.
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paper_title: Sparsity enhancement for blind deconvolution of ultrasonic signals in nondestructive testing application

paper_content:

The received signal in ultrasonic pulse-echo inspection can be modeled as a convolution between an impulse response and the reflection sequence, which is the impulse characteristic of the inspected object. Deconvolution aims at approximately inverting this process to improve the time resolution so that the overlap between echoes from closely spaced reflectors becomes small. This paper presents a modified minimum entropy blind deconvolution algorithm for deconvolving ultrasonic signals. Enhancement of the resolution is achieved by using the presented method. In addition, the presented approach will, in many cases, lead to a faster computation. A nonlinear function is the key point to the efficiency of the modified blind deconvolution algorithm, which is used to increase the sparsity of the iteration output and to decrease the influence of the added noise by replacing each iteration output by output of the nonlinear function. Simulations showed the efficiency of the modification as compared with minimum entropy deconvolution when deconvolving synthetic ultrasonic signals. Experimental results using real ultrasonic data evaluated further that the exact solution consistently yields good performance. The thickness of a thin steel sample can be calculated by the modified blind deconvolution filter with a reasonable accuracy.
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paper_title: Application of regularized deconvolution technique for predicting pavement thin layer thicknesses from ground penetrating radar data

paper_content:

Abstract In this paper, regularized deconvolution is utilized to analyze GPR signal collected from thin asphalt pavement overlays of various mixtures and thicknesses on a test site. By applying regularized deconvolution and the L-curve method, the overlapped interface was identified in the signal. The thickness of the thin layer was predicted with maximum error of 4.2%, which is less than 1.5 mm, a value well below the layer tolerance during construction. The study shows that the algorithm based on regularized deconvolution is a simple and effective approach for processing GPR data collected from thin pavement layers to predict their thickness.
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paper_title: Two-sided deconvolution - A Method to improve the temporal resolution in radar data

paper_content:

Deconvolution is a standard process for the filtering of seismic data. It is primarily used to improve the temporal resolution in the data and to reduce multiple energy. It also has been applied to radar data, but generally with little success. This is mainly due to the non-trivial phase spectrum of the radar wavelet. A deconvolution program has been developed which takes the phase characteristic of the radar wavelet into account and allows the use of arbitrarily shaped model wavelets. The results of the deconvolution of a field data example are presented.
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paper_title: Improving ground-penetrating radar data in sedimentary rocks using deterministic deconvolution

paper_content:

Abstract Resolution is key to confidently identifying unique geologic features using ground-penetrating radar (GPR) data. Source wavelet “ringing” (related to bandwidth) in a GPR section limits resolution because of wavelet interference, and can smear reflections in time and/or space. The resultant potential for misinterpretation limits the usefulness of GPR. Deconvolution offers the ability to compress the source wavelet and improve temporal resolution. Unlike statistical deconvolution, deterministic deconvolution is mathematically simple and stable while providing the highest possible resolution because it uses the source wavelet unique to the specific radar equipment. Source wavelets generated in, transmitted through and acquired from air allow successful application of deterministic approaches to wavelet suppression. We demonstrate the validity of using a source wavelet acquired in air as the operator for deterministic deconvolution in a field application using “400-MHz” antennas at a quarry site characterized by interbedded carbonates with shale partings. We collected GPR data on a bench adjacent to cleanly exposed quarry faces in which we placed conductive rods to provide conclusive groundtruth for this approach to deconvolution. The best deconvolution results, which are confirmed by the conductive rods for the 400-MHz antenna tests, were observed for wavelets acquired when the transmitter and receiver were separated by 0.3 m. Applying deterministic deconvolution to GPR data collected in sedimentary strata at our study site resulted in an improvement in resolution (50%) and improved spatial location (0.10–0.15 m) of geologic features compared to the same data processed without deterministic deconvolution. The effectiveness of deterministic deconvolution for increased resolution and spatial accuracy of specific geologic features is further demonstrated by comparing results of deconvolved data with nondeconvolved data acquired along a 30-m transect immediately adjacent to a fresh quarry face. The results at this site support using deterministic deconvolution, which incorporates the GPR instrument's unique source wavelet, as a standard part of routine GPR data processing.
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paper_title: The deconvolution problem: An overview

paper_content:

This paper is a tutorial review of the deconvolution problem. It reviews the definitions of convolution and deconvolution and discusses both the time-domain and frequency-domain methods of performing deconvolution. The paper identifies the true nature of the practical deconvolution problem as an approximation or estimation problem. And, it discusses the concepts of achieving an "acceptable" solution.
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paper_title: Subsurface radar propagation deconvolution

paper_content:

The frequency dependence of attenuation is typically far greater for subsurface radar waves than for seismic waves. Since this frequency dependence causes the subsurface radar pulse shape to change as it propagates through the earth, conventional wavelet deconvolution techniques are often inadequate to reconstruct the earth’s reflectivity series. The application of a time‐variant filter that undoes the effect of frequency‐dependent attenuation can substantially improve the resolution of subsurface radar data. This filter is minimum‐phase with amplitude characteristics equal to the inverse of the attenuation function of the medium investigated. Preliminary tests on data from surveys over a water tank, an underground mine stope, and fractured granite suggest that good results can also be achieved by assuming attenuation is linearly proportional to frequency, similar to a constant Q model.
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paper_title: Algorithm development for the application of ground-penetrating radar on asphalt pavement compaction monitoring

paper_content:

Ground-penetrating radar (GPR) is a promising non-destructive technique to be applied on monitoring the density change during asphalt pavement compaction. The utmost challenge of this application is the unknown effect of surface moisture, sprayed by the compactor during compaction, on GPR signals. To extract density information without the effect of surface moisture, a correction algorithm based on reference scan approach was developed. To evaluate the performance of the algorithm, a full-scale test site was constructed with compaction pass number from 0 to 10, and a large amount of GPR data were collected from the pavement with different surface moisture contents. A total of 22 cores were extracted for validation purposes. After applying the algorithm, it was found that the average density prediction error was reduced significantly. By using correction algorithm together with the density model, the density of asphalt pavement was obtained with high accuracy.
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paper_title: Blind deconvolution via sparsity maximization applied to GPR data

paper_content:

ABSTRACT In measuring thin layer thickness of asphalt pavements using GPR, the sparse reflectivity series representing the layered structure of the pavement is convolved with the radar wavelet. This convolution results in masking closely spaced reflections. An ideal deconvolution retrieves the reflectivity series, and thus improves the time resolution and facilitates quantitative data interpretation. In this paper, we cast the convolutional model as a multidimensional data model which renders blind deconvolution via independent component analysis possible. We use a nonlinearity related to the double exponential density whose heavy-tailed nature provides further insight into the sparse nature of the reflectivity series. The method is tested on synthetic and real GPR data from a thin PVC slab. The results show the accuracy of the time delay estimates and verify the high resolution capability of the proposed approach.
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paper_title: APPROACH TO DETERMINING IN SITU DIELECTRIC CONSTANT OF PAVEMENTS: DEVELOPMENT AND IMPLEMENTATION AT INTERSTATE 81 IN VIRGINIA

paper_content:

A major problem in using ground penetrating radar (GPR) for estimating pavement layer thickness is assuming the dielectric properties of that layer. Pavement dielectric properties may vary significantly due to aggregate type, moisture presence, and other conditions. Therefore, uncertainties in the dielectric constant, which may vary from 3 to 15, will result in misleading thickness determination. Obtaining cores for calibration may reduce the error, but the variation in the dielectric constant along the roadway often leads to errors in the thickness determination. A method was developed to determine the dielectric constant, and therefore the thickness, of the hot-mix asphalt (HMA) layer of a pavement using GPR. Because of the different compositions and ages of the layers forming HMA in older pavements, dielectric constant estimation based on the surface reflection may not be accurate and may lead to wrong thickness estimations. The developed method uses a modified common midpoint technique (usually used i...
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paper_title: Development of an analytic approach utilizing the extended common midpoint method to estimate asphalt pavement thickness with 3-D ground-penetrating radar

paper_content:

Abstract As a nondestructive technique, ground-penetrating radar (GPR) has been applied to estimate asphalt pavement thickness. The extended common midpoint (XCMP) method is a method that can be used on the air-coupled, pulsed horn antenna to increase the accuracy of asphalt pavement thickness estimation without calibrating the dielectric constant by taking cores. 3-D GPR is a multi-array, stepped-frequency radar that can measure both in-line and cross-line directions at a very close sampling interval. By developing signal-processing and numerical analysis techniques, this research integrates 3-D GPR with the XCMP method. By validating the developed algorithm at a full-scale test site, the study concludes that by using signal processing techniques and numerical analysis approaches, 3-D GPR can be used to accurately predict asphalt layer thickness using the XCMP method when the layer thickness is greater than 64mm.
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paper_title: Accuracy of pavement thicknesses estimation using different ground penetrating radar analysis approaches

paper_content:

The Ground Penetrating Radar (GPR) is a Non-destructive Testing (NDT) technique, which is able to capture continuous pavement layer thicknesses data. The radar pulse propagation is a major factor for gathering the dielectric constants of pavement materials accurately. The present research focuses on the accuracy of pavement asphalt layer thicknesses estimation using GPR data analysis by employing different estimation approaches based on material dielectric properties. A comprehensive comparative analysis of GPR and asphalt-drilled cores data incorporating a variety of pavements is performed. The major findings of the detailed comparative analysis including the effectiveness of the approaches used are reported and discussed in the present paper.
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paper_title: APPROACH TO DETERMINING IN SITU DIELECTRIC CONSTANT OF PAVEMENTS: DEVELOPMENT AND IMPLEMENTATION AT INTERSTATE 81 IN VIRGINIA

paper_content:

A major problem in using ground penetrating radar (GPR) for estimating pavement layer thickness is assuming the dielectric properties of that layer. Pavement dielectric properties may vary significantly due to aggregate type, moisture presence, and other conditions. Therefore, uncertainties in the dielectric constant, which may vary from 3 to 15, will result in misleading thickness determination. Obtaining cores for calibration may reduce the error, but the variation in the dielectric constant along the roadway often leads to errors in the thickness determination. A method was developed to determine the dielectric constant, and therefore the thickness, of the hot-mix asphalt (HMA) layer of a pavement using GPR. Because of the different compositions and ages of the layers forming HMA in older pavements, dielectric constant estimation based on the surface reflection may not be accurate and may lead to wrong thickness estimations. The developed method uses a modified common midpoint technique (usually used i...
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paper_title: An innovative method for measuring pavement dielectric constant using the extended CMP method with two air-coupled GPR systems

paper_content:

Abstract Ground penetrating radar (GPR) is a common non-destructive tool for pavement layer thickness measurement. The accuracy of such measurement is directly affected by the accurate prediction of the dielectric constant of pavement material using GPR. In this study, an innovative extended common mid-point (XCMP) method using two air-coupled GPR systems was developed to improve the accuracy of the traditional method for pavement material dielectric constant estimation. The equations and algorithm for calculating the dielectric constant of pavement material were developed, and then the accuracy of this new method was validated successfully by the data collected from a custom-designed test site.
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paper_title: Seismic velocities from surface measurements

paper_content:

The purpose of this paper is to discuss field and interpretive techniques which permit, in favorable cases, the quite accurate determination of seismic interval velocities prior to drilling. A simple but accurate formula is developed for the quick calculation of interval velocities from “average velocities” determined by the known x2-T2 technique. To secure accuracy a careful study of multiple reflections is necessary and this is discussed. Although the principal objective in determining velocities is to allow an accurate structural interpretation to be made from seismic reflection data, an important secondary objective is to get some lithological information. This is obtained through a correlation of velocities with rock type and depth.
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paper_title: Influence of lithology on radar echoes; analysis with respect to electromagnetic parameters and rock anisotropy

paper_content:

Applying data processing techniques developed for seismology to radar records has assisted in the graphic presentation of radar images and improved signal analysis. Procedure evaluation was based ::: on radar measurements obtained with nominal frequencies of 50, 100 and 200 MHz (Pulse EKKO III). The measurements involved a set of geological ::: formations covering a wide range of the determinate physical parameters for ground penetrating radar (GPR).
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Title: An Overview of Ground-Penetrating Radar Signal Processing Techniques for Road Inspections

Section 1: INTRODUCTION
Description 1: Provide an introduction to the importance of road inspection, highlight safety concerns, and outline the effectiveness of GPR in road engineering.

Section 2: The GPR technique
Description 2: Explain the basic principles of GPR, including how it operates, the properties of electromagnetic waves, and how these waves are used to image subsurface structures.

Section 3: Main GPR configurations
Description 3: Discuss different configurations of GPR systems, such as impulse radar systems, stepped frequency continuous-wave systems, mono-static and bi-static systems, and ground-coupled versus air-coupled antennas.

Section 4: Radar signal imaging
Description 4: Describe the various modes of radar signal imaging including A-scan, B-scan, and C-scan, and explain how each mode is used in road engineering applications.

Section 5: SIGNAL PROCESSING TECHNIQUES IN ROAD INSPECTIONS
Description 5: Provide an overview of the main signal processing techniques employed in GPR datasets for road surveys, categorized by pre-processing, A-scan data processing, and B-scan data processing.

Section 6: Data editing
Description 6: Discuss initial data editing steps such as sorting, handling incorrect settings, dealing with noise, and desaturation functions to prepare for further processing.

Section 7: Time-zero correction
Description 7: Explain the importance of and methods for setting a common time-zero reference point in GPR data for consistency and accurate depth interpretation.

Section 8: Zero offset removal
Description 8: Describe techniques for removing initial DC signal components and low-frequency trends from A-scans to obtain a mean-zero signal.

Section 9: Band-pass filtering
Description 9: Detail the application and types of band-pass filters used to increase the signal-to-noise ratio by filtering out irrelevant frequency components.

Section 10: Time-varying gain
Description 10: Explain the methodology and reasons for applying time-varying gain functions to compensate for signal attenuation due to medium conductivity and geometrical spreading losses.

Section 11: Background removal
Description 11: Describe techniques for removing background noise by subtracting the average value of trace amplitudes to enhance subsurface reflections in B-scan data.

Section 12: Velocity analysis
Description 12: Discuss methods for time-depth conversion of GPR signals, including CMP and hyperbolic velocity analysis, and their importance in accurately reflecting the multi-layered nature of pavements.

Section 13: CONCLUSIONS
Description 13: Summarize the key points discussed in the paper, emphasizing the importance of setting clear objectives, choosing appropriate processing techniques, and ensuring quality data collection for effective GPR surveys in road engineering.