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Journal ArticleDOI

A signal processing methodology for assessing the performance of ASTM standard test methods for GPR systems

01 Mar 2017-Signal Processing (Elsevier)-Vol. 132, pp 327-337
TL;DR: This work proposes a GPR signal processing methodology, calibrated and validated on the basis of a consistent amount of data collected by means of laboratory-scale tests, to assess the performance of the above standard test methods for GPR systems.
About: This article is published in Signal Processing.The article was published on 2017-03-01 and is currently open access. It has received 27 citations till now. The article focuses on the topics: Ground-penetrating radar.

Summary (3 min read)

1. INTRODUCTION

  • Ground penetrating radar (GPR) is an increasingly popular non-destructive testing (NDT) technique that emits a short pulse of electromagnetic energy into the subsurface [1, 2].
  • In Germany, instructions on the use of radar systems for non-destructive testing in civil engineering [10] and for gaining inventory data of road structures [11] are available.
  • Furthermore, a novel pre-processing method for GPR signals, based on the minimum gradient method, is discussed in [28].
  • In line with the above and according to the guidance provided by the mentioned ASTM standards, this paper is (to the best of the authors’ knowledge) the first study that focuses on the ASTM SNR test, thereby aiming at providing a detailed analysis of the bias and variance of the testing variable under consideration (i.e. the SNR).

2. BASIC FRAMEWORK ON GPR PRINCIPLES AND REFERENCE ASTM

  • STANDARDS 2.1 GPR working principles and main applications.
  • The hardware of a GPR system utilized for the measurement of the subsurface conditions usually consists of a transmitter and a receiver antenna, a radar control unit, and suitable data storage and display devices.
  • Measurements can be traditionally performed in two main survey configurations, namely, with ground-coupled or air-coupled antennas, as a function of the main purposes and type of survey.
  • To cite a few, the authors can mention the evaluation of layer thicknesses [44] and subsurface moisture [45, 46], the assessment of damage conditions in hot-mix asphalt (HMA) layers [47], load-bearing layers and subgrade soils [48-51], the inspection of concrete structures [52, 53].

2.2 ASTM standard test methods

  • The ASTM society is an international organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services.
  • For air-launched antennas, four main tests are mentioned and worthy to be verified, namely, i) the signal-to-noise ratio (SNR), ii) the signal stability, iii) the linearity in the time axis and time window accuracy, and iv) the long-term stability test.
  • To the best of the authors’ knowledge, no in-depth study is provided in the literature about the analysis of the compliance with the SNR test of a GPR signal, which conversely appears to be one of the main requirements by the manufacturers.
  • The Standard recommends to perform the SNR test on each of the above 100 waveforms and to take the average signal-to-noise value of the 100 waveforms as reference “signal-to-noise of the system”.

3. SIGNAL PROCESSING METHODOLOGY FOR ASTM STANDARD

  • The SNR test method, as defined by the D 6087 – 08 ASTM Standard [24], is here taken as the reference parameter for assessing the performance of the GPR signals, in terms of bias and variance.
  • Only three papers investigating on the precision of the GPR measurements have been found in the literature.
  • Nevertheless, none of these papers provides any discussion about the precision of the SNR test method, especially in terms of bias.
  • Hence, bias stands for the average difference to be expected between the estimator and the underlying parameter.
  • Afterwards, the authors provide such a discussion in Section 3.2, evaluating the bias and variance of the testing variable under consideration.

3.1 Optimal threshold tuning

  • Nevertheless, no further information is provided on how the threshold has been set, nor to which accuracy (or signal stability) of the GPR equipment this threshold corresponds.
  • The authors provide the signal processing methodology to evaluate the proper threshold for the specific GPR equipment, according to a fixed desired (i.e. target) level of accuracy.
  • First of all, the authors evaluate the SNR of the system as the average SNR over a number of L trials as follows: 𝑆𝑁𝑅 = 1 𝐿 ∙ ∑ 𝑆𝑁𝑅𝑗 𝐿 𝑗=1 , (4) In particular, SNRj is the SNR of the j-th experiment, and defined as the ratio between the mean signal and the noise peaks, respectively.
  • Since all the terms of the sum in (4) represent SNRs of different experiments, they also represent physically independent and hence statistically independent random variables.
  • Then, let us now define with PACC the desired (or target) level of accuracy (in percentage) requested to the GPR system.

3.2 Performance evaluation

  • It is evaluated the performance of the SNR test method, by theoretically assessing the bias and the variance of the estimation error of the testing variable in (4).
  • In the following analysis, the authors first evaluate the bias and the variance of SNR̂𝑗, and then they compute the bias and variance in (11).
  • The algebraic expressions (12) and (13) are trivially derived from a computation of the partial derivatives of the expressions in (4).
  • It has to be noted that both the estimations in (22) and (23) vary with 1/K, meaning that the SNR estimator is consistent (i.e. as the number of considered radar waveforms K becomes larger and larger, the estimate tends to the true value).

4.1 Laboratory set-up

  • Several laboratory-scale tests were performed according to the set-up shown in Fig.
  • This may be mostly due to the deflections induced to the surveying apparatus by the combination of remarkable traffic speeds and damaged conditions of the pavement surface when performing GPR measurements in real roads.
  • Considerations on the signal response in near-field and far-field conditions can also be drawn.
  • The floor under the antennas was covered by a 200 cm × 200 cm copper sheet acting as perfect electric conductor (PEC), and capable to completely reflect the propagation waves and generating a pulse with maximum amplitude.
  • Measurements at each of the aforementioned heights were performed using three air-coupled GPR systems with different central frequencies of 1 and 2 GHz.

4.2 Experimental outcomes

  • The assumptions made in the previous Section have been firstly empirically verified.
  • As in the previous case, the authors can notice a maximum variation of the signal and noise peak within the 6% for the 2 GHZ EU equipment, whereas this value is between the 6-7% in the case of the 2GHz NA system.
  • Variances of the noise peak for 100 consecutive radar traces.
  • Hence, the authors can now evaluate the performance of the SNR test method, by computing the bias and variance of the estimation errors, according to (21) and (22).
  • The threshold value modifies accordingly to h. Figs. 10 and 11 show how the accuracy of the GPR signal varies versus the threshold in the cases of the 2GHZ EU and the 2GHZ NA GPR systems, respectively.

5. CONCLUSION

  • This paper has devised a signal processing methodology for assessing the performance of the international standard test methods released by the American Society for Testing and Materials (ASTM) about the application of GPR techniques.
  • The theoretical expressions for the bias and variance of the estimation error have been evaluated by a reduced Taylor’s expansion up to the second order.
  • Therefore, a closed form expression for theoretically tuning the optimal threshold according to a fixed target value of the GPR signal stability has been proposed.
  • The overall study has been extended to three air-coupled GPR systems with different antennas to analyze the specific relationship between the frequency of investigation, the optimal thresholds, and the signal stability.
  • The results achieved from several trials at the laboratory scale confirm the consistency of such a methodology for assessing the performance of these international standard test methods for GPR systems.

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Citations
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Journal ArticleDOI
TL;DR: In this article , the feasibility of estimating, by using ground-penetrating radar (GPR), the moisture content in asphalt concrete (AC) pavement-construction process is investigated, and a testing protocol for predicting moisture content using GPR is suggested for CIR and CCPR pavement.
Abstract: Ground-penetrating radar (GPR) recently has been used for quality control and quality assurance of the asphalt concrete (AC) pavement-construction process. The objective of this study was to investigate the feasibility of estimating, by using GPR, the moisture content in AC pavement. This application is particularly important for emulsion-stabilized cold in-place recycling (CIR) and cold central-plant recycling (CCPR), where monitoring the moisture content is necessary for deciding the timing of opening the road to traffic, overlay placement, or both. Four field tests were performed using GPR on CIR- or CCPR-treated AC pavement. A numerical simulation model of AC pavement with internal moisture was generated using the information from mix design, and virtual GPR tests were performed using the finite-difference time-domain (FDTD) method. After calibration, a moisture-prediction formula derived from the simulation model was used to correlate the dielectric constant predicted by GPR to the moisture content within cold recycled layers. The GPR signal was “denoised” by improving its stability and mitigating the measured-height mismatch. The in-situ moisture content was predicted using the proposed method and compared with field-collected samples. Results showed that the proposed method is effective in estimating CIR- and CCPR-layer moisture content. The variation of dielectric constants in field tests is also discussed. A testing protocol for predicting moisture content using GPR is suggested for CIR and CCPR pavement.

2 citations

Journal ArticleDOI
TL;DR: In this paper , a ground penetrating radar (GPR) survey employing a concrete scanning system with a shielded 1.2 GHz center frequency was performed on self-consolidating casted short beams just before a monotonic four-point bending test was carried out.
Book ChapterDOI
01 Jan 2023
TL;DR: In this article , the authors presented the design of a capnography tool using high-performance infrared CO 2 sensor and low-cost electronic components integrated with algorithms for extraction of capnogram features for monitoring asthmatic condition of a patient.
Abstract: With reference to the details shared in previous chapters, this chapter is on the design of carbon dioxide (CO 2 ) measuring tool to monitor asthmatic conditions. The presented work emphasizes the design of capnography tool using high-performance infrared CO 2 sensor and low-cost electronic components integrated with algorithms for extraction of capnogram features for monitoring asthmatic condition of a patient. With reference to the previous chapters, this chapter presents the design of capnography in detection and monitoring asthma. The design involves utilization of CO 2 sensor and the computer-based algorithm for the acquisition of CO 2 gas and classification of asthma and nonasthma. The capnograph device detects the exhaled CO 2 ; generates capnogram waveform; assesses the capnogram features and discloses the asthmatic condition. Hereby, the developed strategy discriminates the presence and absence of asthma based on the capnogram waveform features. The capnography device generated is able to display capnogram waveform and the numerical values in response to the breathing condition of a subject, which have shown an appealing interest for rapid diagnosis of asthmatic conditions.
Proceedings ArticleDOI
01 Jun 2017
TL;DR: In this article, the authors used step frequency radar (SFR) to assess the compactness of a Hot Mix Asphalt (HMA) in a new paved highway containing 38 % in weight of unknown recycled component.
Abstract: The aim of this work is to show the relevance use of the Step Frequency Radar (SFR) to assess the compactness of a Hot Mix Asphalt (HMA). Herein, compactness assessment of a new paved highway containing 38 % in weight of unknown recycled component is performed through SFR. Three different methods of analysis are developed to assess accurately the compactness of the investigated road. The first method does not require lab measurement or core drilling. The second method is based on laboratory measurements of aggregate permittivity. Finally, the third method leans on lab measurements and core drilling calibration. It turns out that the calibration through core drilling was not necessary for reaching the 1 % accuracy mandated for the compactness assessment. The effect of the roughness on the reflected signals is investigated and highlights that a correlation with the high HMA roughness and the scattering obtained with SFR can be performed. The influence of the properties in the electromagnetic models was investigated and shows that the knowledge of the main component permittivity of the HMA is primordial to assess accurately the compactness.

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References
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Book ChapterDOI
15 Apr 2005
TL;DR: The ground penetrating radar (GPR) is a nondestructive measurement technique which uses electromagnetic waves to locate targets or interfaces buried within a visually opaque substance or Earth material.
Abstract: Ground penetrating radar (GPR) is a nondestructive measurement technique, which uses electromagnetic waves to locate targets or interfaces buried within a visually opaque substance or Earth material. GPR is also termed ground probing, surface penetrating (SPR), or subsurface radar. A GPR transmits a regular sequence of low-power packets of electromagnetic energy into the material or ground, and receives and detects the weak reflected signal from the buried target. The buried target can be a conductor, a dielectric, or combinations of both. There are now a number of commercially available equipments, and the technique is gradually developing in scope and capability. GPR has also been used successfully to provide forensic information in the course of criminal investigations, detect buried mines, survey roads, detect utilities, measure geophysical strata, and in other applications. Keywords: ground penetrating radar; ground probing radar; surface penetrating radar; subsurface radar; electromagnetic waves

1,082 citations


"A signal processing methodology for..." refers background in this paper

  • ...Ground penetrating radar (GPR) is an increasingly popular nondestructive testing (NDT) technique that emits a short pulse of electromagnetic energy into the subsurface [1,2]....

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DatasetDOI
TL;DR: A non-destructive technique using electromagnetic waves to locate objects or interfaces buried in the ground has been proposed in this article, which can be used to locate buried objects and interfaces.
Abstract: A nondestructive technique using electromagnetic waves to locate objects or interfaces buried benea…

626 citations

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TL;DR: A status report of ground-penalizing radar (GPR) highway applications is provided in this paper based on studies conducted in both Scandinavia and the USA, where ground-coupled and air-launched GPR systems together with a discussion of both signal processing and data interpretation techniques are discussed.

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  • ...Accordingly, the testing variable in (4) is asymptotically (L - 1) Gaussian as a direct consequence of the central limit theorem [60]....

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Frequently Asked Questions (1)
Q1. What contributions have the authors mentioned in the paper "A signal processing methodology for assessing the performance of astm standard test methods for gpr systems" ?

This work proposes a GPR signal processing methodology, calibrated and validated on the basis of a consistent amount of data collected by means of laboratory-scale tests, to assess the performance of the above standard test methods for GPR systems. Finally, the study is extended to GPR systems with different antenna frequencies to analyze the specific relationship between the frequency of investigation, the optimal thresholds, and the signal stability.