Ground-penetrating radar theory and application of thin-bed offset-dependent reflectivity

Bradford, John H.; Deeds, Jacob C.

doi:10.1190/1.2194524

Cited by 85 publications

(81 citation statements)

References 36 publications

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“…Eq. (7), modified from [8], describes the relationship between the amplitude measured by the radar (A obs ) and the amplitude of the signal originally emitted by the antenna (A source ): In eq. (7), C and P represent respectively the coupling factor with the ground and the radiation pattern for the emitter and receiver antennas, while r is the depth of the thin layer and α (dB/m) is the attenuation factor [2].…”

Section: 4mentioning

confidence: 99%

Static Detection of Thin Layers into Concrete with Ground Penetrating Radar

Wielen

Courard

Nguyen

2012

Restoration of Buildings and Monuments

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Ground Penetrating Radar (GPR) is a nondestructive technique particularly well adapted to the inspection of concrete structures and can help to determine the structure inner geometry or to detect damaged areas. When the GPR is used on structures containing thin layers, for example the sealing layer of a concrete bridge deck or the void into a masonry wall, it is important for the radar user to know the minimum thickness required to detect and estimate the thickness of those layers.The theory of thin layer detection is based on a sine wave but, in reality, most commercial GPR systems emit a large frequency band wavelet, which undergoes attenuation into the layer. To analyze the influence of those realistic conditions on the reflection coefficient of a thin layer, we combined experimental measurements and numerical FDTD simulations. The experimental results matched the numerical predictions well, presenting a fast attenuation compared to the theoretical predictions. Nevertheless, for thicknesses inferior to λ/11, the reflection coefficient could still be considered as linearly dependent of the thickness to wavelength ratio.

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Section: 4mentioning

confidence: 99%

Static Detection of Thin Layers into Concrete with Ground Penetrating Radar

Wielen

Courard

Nguyen

2012

Restoration of Buildings and Monuments

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“…Successful application of thin bed AVA analysis in characterizing hydrocarbon contamination in the subsurface suggests the method can be extended to subsurface fracture characterization as both targets are similar i.e. thin beds (Bradford and Deeds, 2006). Deparis and Garambois (2009) studied dispersive frequency dependent amplitude and phase variation with offset (APVO) curves for a restricted case of a thin bed embedded within a homogeneous rock and assessed its potential for characterizing the aperture and fill of such layers.…”

Section: Introductionmentioning

confidence: 99%

“…GPR thin bed reflectivity is sensitive to host media properties (dielectric permittivity, electrical conductivity and magnetic permeability), signal characteristics (frequency, polarization and angle of incidence) and also depends on the thin bed properties i.e. aperture and fill (Hollender and Tillard, 1998, Innan and Innan, 2000, Bradford and Deeds, 2006, Deparis and Garambois, 2009). The sensitivity of thin bed reflectivity has been explored e.g.…”

Section: Introductionmentioning

confidence: 99%

“…Applying the analysis to GPR data, Deeds and Bradford (2002) successfully characterized the presence of an NAPL contaminated zone at an alluvium/clay boundary. Bradford and Deeds (2006) investigated the AVA response of a thin bed and proposed a validity limit of the standard…”

Section: Introductionmentioning

confidence: 99%

“…Fractures therefore, have apertures less than at the dominant frequency of the GPR signal and as such generate complex reflectivity patterns as a result of interference from multiple reflections from their surfaces (figure 1). In order to characterize reflectivity of such fractures, thin bed analysis is necessary (Bradford and Deeds, 2006). GPR thin bed reflectivity is sensitive to host media properties (dielectric permittivity, electrical conductivity and magnetic permeability), signal characteristics (frequency, polarization and angle of incidence) and also depends on the thin bed properties i.e.…”

Section: Introductionmentioning

confidence: 99%

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Fracture aperture and fill characterization in a limestone quarry using GPR thin‐layer AVA analysis

Kana¹,

West²,

Clark³

2012

Near Surface Geophysics

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The detection and characterization of fractures is important in many engineering practices e.g., rock fall assessment, quarry rock quality determination and mine roof and tunnel stability. Fractures may provide suitable contrasts in electrical properties for detection by GPR instruments. Their ability to reflect radar waves and the dependence of this reflectivity on fracture properties (aperture and fill) makes the GPR method a promising tool for rock fracture characterization. Doing so successfully requires quantification of the reflectivity, reflection coefficient, R, of individual fractures and its variation with incidence angle (AVA), or in practice, offset. Measuring the full AVA response using Common Mid Point (CMP) surveys enables simultaneous estimation of fracture aperture and fill permittivity, difficult to achieve with Common Offset (CO) profiling which does not evaluate angle dependence. This paper reports on AVA analysis carried out on CMP data acquired with 500 MHz antennae over Carboniferous Limestone with horizontal bedding plane fractures in Yorkshire, United Kingdom. Using the transverse electric (TE) polarization mode, data were collected at a sampling interval of 0.05 ns for offsets at 0.04 m steps from 0.37–16.05m. The recorded amplitude is related to the reflection coefficient but is also influenced by other factors we eliminated by making some simplifying assumptions and amplitude corrections. We assume frequency‐independent electrical properties, constant antenna coupling with the ground surface, constant losses associated with transmission losses through any interfaces above the target reflection for the range of offsets considered and a flat homogeneous surface over which measurements are made. Amplitudes were corrected for conductive attenuation, spherical spreading and antenna patterns, which we measured through transillumination surveys across limestone boulders and numerical modelling using the GprMax 3D modelling code. To constrain fracture aperture and fill permittivity, we use the least squares fit of normalized reflection coefficient curves to corrected CMP amplitudes. The analysis allowed characterization of the (bedding plane) fracture fill relative permittivity (~7.8) and aperture (~0.043 m, ~0.2λ at 500 MHz). The values obtained are consistent with field observations of fracture fill, corresponding to a mixture of clays and calcite.

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Hydrogeophysical characterization of transport processes in fractured rock by combining push‐pull and single‐hole ground penetrating radar experiments

Shakas

Linde

Baron

et al. 2016

Water Resources Research

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International audienceThe in situ characterization of transport processes in fractured media is particularly challenging dueto the considerable spatial uncertainty on tracer pathways and dominant controlling processes, suchas dispersion, channeling, trapping, matrix diffusion, ambient and density driven flows. Weattempted to reduce this uncertainty by coupling push-pull tracer experiments with single-holeground penetrating radar (GPR) time-lapse imaging. The experiments involved different injectionfractures, chaser volumes and resting times, and were performed at the fractured rock research siteof Ploemeur in France (H+ network, hplus.ore.fr/en). For the GPR acquisitions we used both fixedand moving antenna setups in a borehole that was isolated with a flexible liner. During the fixedantennaexperiment, time-varying GPR reflections allowed us to track the spatial and temporaldynamics of the tracer during the push-pull experiment. During the moving antenna experiments,we clearly imaged the dominant fractures in which tracer transport took place, fractures in whichthe tracer was trapped for longer time periods and the spatial extent of the tracer distribution (up to8 meters) at different times. This demonstrated the existence of strongly channelized flow in thefirst few meters and radial flow at greater distances. By varying the resting time of a givenexperiment, we identified regions affected by density-driven and ambient flow. These experimentsopen up new perspectives for coupled hydrogeophysical inversion aimed at understanding transportphenomena in fractured rock formations

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Ground-penetrating radar theory and application of thin-bed offset-dependent reflectivity

Cited by 85 publications

References 36 publications

Static Detection of Thin Layers into Concrete with Ground Penetrating Radar

Static Detection of Thin Layers into Concrete with Ground Penetrating Radar

Fracture aperture and fill characterization in a limestone quarry using GPR thin‐layer AVA analysis

Hydrogeophysical characterization of transport processes in fractured rock by combining push‐pull and single‐hole ground penetrating radar experiments

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