Spectral absorption of spatial and temporal ground penetrating radar signals by water in construction materials

Lai, Wallace Wai-Lok; Kind, Thomas; Kruschwitz, Sabine; Wöstmann, Jens; Wiggenhauser, Herbert

doi:10.1016/j.ndteint.2014.06.009

Cited by 34 publications

(19 citation statements)

References 23 publications

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“…The travel time between reflections can be converted into an average velocity for a particular point within a construction, which under certain assumptions can be used to calculate the dielectric constant: a physical property that is strongly influenced by water content [43]. Additionally, the amplitude of the surface (direct) wave is strongly dependent on water content and can be used as a proxy for near-surface water contents [44]. Both radar characteristics have been shown to calibrate well over a range of moisture contents for porous building materials [27] and are investigated here.…”

Section: Monitoringmentioning

confidence: 99%

Moisture monitoring of stone masonry: A comparison of microwave and radar on a granite wall and a sandstone tower

Orr

Fusade

Young

et al. 2020

Journal of Cultural Heritage

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Water is a fundamental control on the deterioration of historic stone masonry, of which wind-driven rain (WDR) is an important source in the UK. Non-destructive testing methods for moisture measurement can characterise the response of masonry to short (but intense) periods of wind-driven rain. An important part of this response is how masonry functions as a system of stone units and mortar joints, in which mortar can act as a conduit for moisture. While non-destructive techniques are common in moisture surveying of built heritage, there are no agreed best practice methods for collection, handling, and visual representation of data. This study explores the comparative advantages of microwave and radar measurements in two field experiments of exposure to short (but intense) simulated wind-driven rain exposure to demonstrate when and how they are most effectively employed. A novel method of representing data as percentiles is explored to facilitate effective communication of moisture measurements. In the case of the granite wall (e.g. with components of strongly contrasting hygric properties), microwave and radar provided similar information. The average travel time of the radar signal (from the back wall reflection) demonstrated that radar can non-destructively identify water penetration through mortar joints. In the sandstone tower, the microwave measurements were able to clearly identify four different moisture regimes as a result of different intensities of WDR exposure. The radar measurements were suited to identifying distinctions between localised moisture contents within masonry units and mortar joints, which characterised how the masonry was functioning as a holistic system. The measurements on both the granite wall and the sandstone tower demonstrated that the radar is influenced by environmental conditions which influence surface condensation and equilibrium moisture contents. Representing the measurements as percentiles improved visual representation of measurements with colour scales and minimised potential skewing of normalisation and scales from extreme values/outliers. This paper demonstrates that both microwave and radar techniques can be useful for monitoring moisture in stone masonry systems. Material characteristics of the masonry system and the objective(s) of the investigation should be considered during selection of the appropriate technique(s).

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Section: Monitoringmentioning

confidence: 99%

Moisture monitoring of stone masonry: A comparison of microwave and radar on a granite wall and a sandstone tower

Orr

Fusade

Young

et al. 2020

Journal of Cultural Heritage

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“…The use of electromagnetic (EM) waves for the characterization of concrete moisture, either by GPR [1][2][3] or by capacitive methods has been investigated by many researchers. Indeed, the complex permittivity (both real and imaginary parts) of concrete is significantly influenced by moisture [4][5][6]. So the development of a probe able to measure complex permittivity of concrete, especially on site, is of great interest.…”

Section: Introductionmentioning

confidence: 99%

Permittivity measurement of cementitious materials and constituents with an open-ended coaxial probe: combination of experimental data, numerical modelling and a capacitive model

Guihard

Taillade

Balayssac³

et al. 2019

RILEM Tech Lett

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The study presents the development of a new two-dimensional FEM numerical model describing the operation of two large open-ended coaxial probes designed to investigate the permittivity of concrete, and its constituents. This numerical simulation, combined with a capacitive approach describing the behaviour of the probes, enabled to prove the suitability of such device to determine the permittivity of dispersive dielectrics. Finding back the permittivity of a specified material by calculation of the S parameters, change of the reference plane and use of the capacitive model is the key to the proof. Measurements performed onto different materials show good similarities with the numerical simulations. Special considerations are mentioned concerning the size of the probe and its ability to measure the permittivity of heterogeneous materials made of large inclusions. Combination of such numerical tool and measuring device can be used as a non-destructive testing technique to assess the near surface permittivity of concrete structures or as a calibration technique for GPR measurements.

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“…Wavelet transform was used in the time-frequency domain, and the algorithm is described in the following section. Advantages of which are reported in Lai et al [3].…”

Section: B Processing In Frequency Domainmentioning

confidence: 97%

“…C. Processing in time-frequency domain Time-frequency domain is able to express two types of information in one single plot, which makes it easier for data interpretation as the evolving and dispersive frequency content of the non-stationary GPR signals is correlated to the time axis. The plot can be produced by transforming the A-scans into a frequency map where the x-axis and y-axis represent the time and frequency respectively, and hence, the frequency distribution is spatially expressed across time [3].…”

Section: B Processing In Frequency Domainmentioning

confidence: 99%

Time-frequency spectral analysis of step frequency continuous wave and impulse ground penetrating radar

Wong

Lai

Suzuki

2016

2016 16th International Conference on Ground Penetrating Radar (GPR)

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Time-frequency spectral responses of an in-house built step-frequency continuous wave (SFCW) GPR (Yakumo) developed by Tohoku University and a commercial impulse GPR were studied and compared. The Yakumo SFCW GPR operates from 50MHz to 1.5GHz, and the center frequency of the commercial impulse GPR is 500MHz. Both GPRs were probed on top of an embedded steel pipe overlaid by a concrete pavement. The time domain radargram signals were transformed to time-frequency domain through continuous wavelet transform with Morlet wavelet as the mother wavelet. The study reveals, with a definite buried pipe as a reflector, how the spectral responses in both frequency domain and time-frequency domain are changed by two different bandwidths and two different ray paths of the GPR wave propagation into materials.

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Spectral absorption of spatial and temporal ground penetrating radar signals by water in construction materials

Cited by 34 publications

References 23 publications

Moisture monitoring of stone masonry: A comparison of microwave and radar on a granite wall and a sandstone tower

Moisture monitoring of stone masonry: A comparison of microwave and radar on a granite wall and a sandstone tower

Permittivity measurement of cementitious materials and constituents with an open-ended coaxial probe: combination of experimental data, numerical modelling and a capacitive model

Time-frequency spectral analysis of step frequency continuous wave and impulse ground penetrating radar

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