scholarly journals Ground-penetrating-radar response to fracture-fluid salinity: Why lower frequencies are favorable for resolving salinity changes

Geophysics ◽  
2008 ◽  
Vol 73 (5) ◽  
pp. J25-J30 ◽  
Author(s):  
Georgios P. Tsoflias ◽  
Matthew W. Becker
Keyword(s):  
Electrical Conductivity ◽  
Ground Penetrating Radar ◽  
Field Experiments ◽  
Fractured Rock ◽  
Low Frequency ◽  
Signal Amplitude ◽  
Time Lapse ◽  
Fracture Aperture ◽  
Fracture Fluid ◽  
Ground Penetrating

Time-lapse ground-penetrating-radar (GPR) surveys exploit signal-amplitude changes to monitor saline tracers in fractures and to identify groundwater flow paths. However, the relationships between GPR signal amplitude, phase, and frequency with fracture aperture and fluid electrical conductivity are not well understood. We used analytical modeling, numerical simulations, and field experiments of multifrequency GPR to investigate these relationships for a millimeter-scale-aperture fracture saturated with water of varying salinity. We found that the response of lower-frequency radar signals detects changes in fluid salinity better than the response of higher-frequency signals. Increasing fluid electrical conductivity decreases low-frequency GPR signal wavelength, which improves its thin-layer resolution capability. We concluded that lower signal frequencies, such as [Formula: see text], and saline tracers of up to [Formula: see text] conductivity are preferable when using GPR to monitor flow in fractured rock. Furthermore, we found that GPR amplitude and phase responses are detectable in the field and predictable by EM theory and modeling; therefore, they can be related to fracture aperture and fluid salinity for hydrologic investigations of fractured-rock flow and transport properties.

scholarly journals Computing Localized Breakthrough Curves and Velocities of Saline Tracer from Ground Penetrating Radar Monitoring Experiments in Fractured Rock

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2949
Author(s):  
Peter-Lasse Giertzuch ◽  
Alexis Shakas ◽  
Joseph Doetsch ◽  
Bernard Brixel ◽  
Mohammadreza Jalali ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Ground Penetrating Radar ◽  
Fractured Rock ◽  
Time Lapse ◽  
Test Site ◽  
Breakthrough Curves ◽  
Flow Path ◽  
Transport Processes ◽  
Grimsel Test Site ◽  
Ground Penetrating

Solute tracer tests are an established method for the characterization of flow and transport processes in fractured rock. Such tests are often monitored with borehole sensors which offer high temporal sampling and signal to noise ratio, but only limited spatial deployment possibilities. Ground penetrating radar (GPR) is sensitive to electromagnetic properties, and can thus be used to monitor the transport behavior of electrically conductive tracers. Since GPR waves can sample large volumes that are practically inaccessible by traditional borehole sensors, they are expected to increase the spatial resolution of tracer experiments. In this manuscript, we describe two approaches to infer quantitative hydrological data from time-lapse borehole reflection GPR experiments with saline tracers in fractured rock. An important prerequisite of our method includes the generation of GPR data difference images. We show how the calculation of difference radar breakthrough curves (DRBTC) allows to retrieve relative electrical conductivity breakthrough curves for theoretically arbitrary locations in the subsurface. For sufficiently small fracture apertures we found the relation between the DRBTC values and the electrical conductivity in the fracture to be quasi-linear. Additionally, we describe a flow path reconstruction procedure that allows computing approximate flow path distances using reflection GPR data from at least two boreholes. From the temporal information during the time-lapse GPR surveys, we are finally able to calculate flow-path averaged tracer velocities. Our new methods were applied to a field data set that was acquired at the Grimsel Test Site in Switzerland. DRBTCs were successfully calculated for previously inaccessible locations in the experimental rock volume and the flow path averaged velocity field was found to be in good accordance with previous studies at the Grimsel Test Site.

Time-lapse ground penetrating radar difference reflection imaging of saline tracer flow in fractured rock

Geophysics ◽  
2020 ◽  
Vol 85 (3) ◽  
pp. H25-H37 ◽  
Author(s):  
Peter-Lasse Giertzuch ◽  
Joseph Doetsch ◽  
Mohammadreza Jalali ◽  
Alexis Shakas ◽  
Cédric Schmelzbach ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Fractured Rock ◽  
Sampling Rate ◽  
Time Lapse ◽  
Transport Processes ◽  
Local Data ◽  
Tracer Injection ◽  
Flow Through ◽  
Reflection Imaging ◽  
Ground Penetrating

The characterization of flow and transport processes in fractured rock is challenging because they cannot be observed directly and hydrologic tests can only provide sparse and local data. Time-lapse ground penetrating radar (GPR) can be a valuable tool to monitor such processes in the subsurface, but it requires highly reproducible data. As part of a tracer injection experiment at the Grimsel Test Site (GTS) in Switzerland, borehole reflection GPR data were acquired in a time-lapse survey to monitor saline tracer flow through a fracture network in crystalline rock. Because the reflections from the tracer in the sub-mm fractures appear extremely weak, a differencing approach has been necessary to identify the tracer signal. Furthermore, several processing steps and corrections had to be applied to meet the reproducibility requirements. These steps include (1) single-trace preprocessing, (2) temporal trace alignment, (3) correction of sampling rate fluctuations, (4) spatial trace alignment, (5) spike removal, and (6) postprocessing procedures applied to the difference images. This allowed successful tracer propagation monitoring with a clear signal that revealed two separate tracer flow paths. The GPR results are confirmed by conductivity meters that were placed in boreholes in the GTS. If sufficient data processing is applied, GPR is shown to be capable of resolving tracer flow through sub-mm aperture fractures by difference reflection imaging even in challenging surroundings where many reflectors are present.

scholarly journals Influence of Concrete Carbonation on Electromagnetic Permittivity Measured by GPR and Capacitive Techniques

2018 ◽  
Vol 23 (4) ◽  
pp. 443-456
Author(s):  
Xavier Dérobert ◽  
Géraldine Villain ◽  
Jean-Paul Balayssac
Keyword(s):  
Complex Permittivity ◽  
Ground Penetrating Radar ◽  
Low Frequency ◽  
Signal Amplitude ◽  
Radar Signal ◽  
Reinforced Concrete Structures ◽  
Concrete Carbonation ◽  
Ground Penetrating ◽  
Non Destructive ◽  
Non Destructive Techniques

This paper addresses the effect of concrete carbonation on the propagation and dispersion of electromagnetic (EM) waves and the capability of two EM, non-destructive techniques to detect this pathology. A capacitive technique operating at low frequency (around 33 MHz) and a ground penetrating radar (GPR) with a 1.5 GHz antenna were tested for the monitoring of reinforced concrete structures. To better understand the phenomena involved in concrete carbonation, the results of two complementary experimental campaigns were analyzed for saturated concretes. First, the dispersion curves of complex permittivity were measured for both carbonated and non-carbonated samples by a cylindrical coaxial EM cell. Due to carbonation, the permittivity decreased and the level of dispersion reduced slightly. Second, using GPR (coupled at approximately 900 MHz) and capacitive measurements conducted on controlled slabs, it was confirmed that the real part of the relative permittivity decreased within a range of 2 at 33 MHz and a range of 1 to 900 MHz, while the radar signal amplitude increased.

scholarly journals Four-dimensional tracer flow reconstruction in fractured rock through borehole ground-penetrating radar (GPR) monitoring

Solid Earth ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 1497-1513
Author(s):  
Peter-Lasse Giertzuch ◽  
Joseph Doetsch ◽  
Alexis Shakas ◽  
Mohammadreza Jalali ◽  
Bernard Brixel ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Fractured Rock ◽  
Time Lapse ◽  
Test Site ◽  
Crystalline Rock ◽  
Flow Paths ◽  
Tracer Injection ◽  
Flow Reconstruction ◽  
Fracture Apertures ◽  
Ground Penetrating

Abstract. Two borehole ground-penetrating radar (GPR) surveys were conducted during saline tracer injection experiments in fully saturated crystalline rock at the Grimsel Test Site in Switzerland. The saline tracer is characterized by an increased electrical conductivity in comparison to formation water. It was injected under steady-state flow conditions into the rock mass that features sub-millimeter fracture apertures. The GPR surveys were designed as time-lapse reflection GPR from separate boreholes and a time-lapse transmission survey between the two boreholes. The local increase in conductivity, introduced by the injected tracer, was captured by GPR in terms of reflectivity increase for the reflection surveys, and attenuation increase for the transmission survey. Data processing and difference imaging was used to extract the tracer signal in the reflection surveys, despite the presence of multiple static reflectors that could shadow the tracer reflection. The transmission survey was analyzed by a difference attenuation inversion scheme, targeting conductivity changes in the tomography plane. By combining the time-lapse difference reflection images, it was possible to reconstruct and visualize the tracer propagation in 3D. This was achieved by calculating the potential radially symmetric tracer reflection locations in each survey and determining their intersections, to delineate the possible tracer locations. Localization ambiguity imposed by the lack of a third borehole for a full triangulation was reduced by including the attenuation tomography results in the analysis. The resulting tracer flow reconstruction was found to be in good agreement with data from conductivity sensors in multiple observation locations in the experiment volume and gave a realistic visualization of the hydrological processes during the tracer experiments. Our methodology was demonstrated to be applicable for monitoring tracer flow and transport and characterizing flow paths related to geothermal reservoirs in crystalline rocks, but it can be transferred in a straightforward manner to other applications, such as radioactive repository monitoring or civil engineering projects.

Seismic reflection and ground‐penetrating radar imaging of a shallow aquifer

Geophysics ◽  
1998 ◽  
Vol 63 (4) ◽  
pp. 1310-1317 ◽  
Author(s):  
Steven J. Cardimona ◽  
William P. Clement ◽  
Katharine Kadinsky‐Cade
Keyword(s):  
Water Table ◽  
Ground Penetrating Radar ◽  
Low Frequency ◽  
Shallow Aquifer ◽  
Cone Penetrometer ◽  
Gradual Change ◽  
Cone Penetration ◽  
Geotechnical Data ◽  
Radar Images ◽  
Ground Penetrating

In 1995 and 1996, researchers associated with the US Air Force’s Phillips and Armstrong Laboratories took part in an extensive geophysical site characterization of the Groundwater Remediation Field Laboratory located at Dover Air Force Base, Dover, Delaware. This field experiment offered an opportunity to compare shallow‐reflection profiling using seismic compressional sources and low‐frequency ground‐penetrating radar to image a shallow, unconfined aquifer. The main target within the aquifer was the sand‐clay interface defining the top of the underlying aquitard at 10 to 14 m depth. Although the water table in a well near the site was 8 m deep, cone penetration geotechnical data taken across the field do not reveal a distinct water table. Instead, cone penetration tests show a gradual change in electrical properties that we interpret as a thick zone of partial saturation. Comparing the seismic and radar data and using the geotechnical data as ground truth, we have associated the deepest coherent event in both reflection data sets with the sand‐clay aquitard boundary. Cone penetrometer data show the presence of a thin lens of clays and silts at about 4 m depth in the north part of the field. This shallow clay is not imaged clearly in the low‐frequency radar profiles. However, the seismic data do image the clay lens. Cone penetrometer data detail a clear change in the soil classification related to the underlying clay aquitard at the same position where the nonintrusive geophysical measurements show a change in image character. Corresponding features in the seismic and radar images are similar along profiles from common survey lines, and results of joint interpretation are consistent with information from geotechnical data across the site.

Laboratory test of snow wetness influence on electrical conductivity measured with ground penetrating radar

2009 ◽  
Vol 40 (1) ◽  
pp. 33-44 ◽  
Author(s):  
Nils Granlund ◽  
Angela Lundberg ◽  
James Feiccabrino ◽  
David Gustafsson
Keyword(s):  
Electrical Conductivity ◽  
Electrical Properties ◽  
Laboratory Test ◽  
Liquid Water ◽  
Ground Penetrating Radar ◽  
Wave Attenuation ◽  
Radar Measurements ◽  
Ground Penetrating ◽  
Radar Wave ◽  
The Relationship

Ground penetrating radar operated from helicopters or snowmobiles is used to determine snow water equivalent (SWE) for annual snowpacks from radar wave two-way travel time. However, presence of liquid water in a snowpack is known to decrease the radar wave velocity, which for a typical snowpack with 5% (by volume) liquid water can lead to an overestimation of SWE by about 20%. It would therefore be beneficial if radar measurements could also be used to determine snow wetness. Our approach is to use radar wave attenuation in the snowpack, which depends on electrical properties of snow (permittivity and conductivity) which in turn depend on snow wetness. The relationship between radar wave attenuation and these electrical properties can be derived theoretically, while the relationship between electrical permittivity and snow wetness follows a known empirical formula, which also includes snow density. Snow wetness can therefore be determined from radar wave attenuation if the relationship between electrical conductivity and snow wetness is also known. In a laboratory test, three sets of measurements were made on initially dry 1 m thick snowpacks. Snow wetness was controlled by stepwise addition of water between radar measurements, and a linear relationship between electrical conductivity and snow wetness was established.

scholarly journals Quantitative high-resolution observations of soil water dynamics in a complicated architecture using time-lapse ground-penetrating radar

2015 ◽  
Vol 19 (3) ◽  
pp. 1125-1139 ◽  
Author(s):  
P. Klenk ◽  
S. Jaumann ◽  
K. Roth
Keyword(s):  
High Resolution ◽  
Water Content ◽  
Soil Water ◽  
Ground Penetrating Radar ◽  
Time Lapse ◽  
Test Site ◽  
Water Dynamics ◽  
Soil Water Dynamics ◽  
Capillary Fringe ◽  
Ground Penetrating

Abstract. High-resolution time-lapse ground-penetrating radar (GPR) observations of advancing and retreating water tables can yield a wealth of information about near-surface water content dynamics. In this study, we present and analyze a series of imbibition, drainage and infiltration experiments that have been carried out at our artificial ASSESS test site and observed with surface-based GPR. The test site features a complicated but known subsurface architecture constructed with three different kinds of sand. It allows the study of soil water dynamics with GPR under a wide range of different conditions. Here, we assess in particular (i) the feasibility of monitoring the dynamic shape of the capillary fringe reflection and (ii) the relative precision of monitoring soil water dynamics averaged over the whole vertical extent by evaluating the bottom reflection. The phenomenology of the GPR response of a dynamically changing capillary fringe is developed from a soil physical point of view. We then explain experimentally observed phenomena based on numerical simulations of both the water content dynamics and the expected GPR response.

scholarly journals Detecting infiltrated water and preferential flow pathways through time-lapse ground-penetrating radar surveys

2020 ◽  
Vol 726 ◽  
pp. 138511 ◽  
Author(s):  
Simone Di Prima ◽  
Thierry Winiarski ◽  
Rafael Angulo-Jaramillo ◽  
Ryan D. Stewart ◽  
Mirko Castellini ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Preferential Flow ◽  
Time Lapse ◽  
Flow Pathways ◽  
Preferential Flow Pathways ◽  
Ground Penetrating
Sign in / Sign up

Export Citation Format

Share Document