Passive Cooperative Targets for Subsurface Physical and Chemical Measurements: A Systems Perspective

Friedt, Jean‐Michel

doi:10.1109/lgrs.2017.2681901

Cited by 14 publications

(16 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Contrary to what Friedt (2017) and Giertzuch et al (2020) have described, we did not encounter significant sampling rate variations or drifts. The greater stability in sampling rate can be likely attributed to the use of the older MALÅ console CU2 instead of the MALÅ ProEx model.…”

Section: Difference Reflection Imagingcontrasting

confidence: 99%

4D Tracer Flow Reconstruction in Fractured Rock through Borehole GPR Monitoring

Giertzuch¹,

Doetsch²,

Shakas³

et al. 2021

Preprint

View full text Add to dashboard Cite

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-mm 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 into 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 proved to be successful for characterizing flow paths related with 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.

show abstract

Section: Difference Reflection Imagingcontrasting

confidence: 99%

4D Tracer Flow Reconstruction in Fractured Rock through Borehole GPR Monitoring

Giertzuch¹,

Doetsch²,

Shakas³

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

“…We have reported [ 49 ] the excessive timebase drift of a commercial GPR, Malå’s ProEx. As a reminder of the core result of this past investigation, we have observed when probing a SAW delay line in a fixed environment that due to the instrument timebase drift, the time delay between echoes appeared to be shifting by 15,000 ppm (1.5%, as observed through a 4.5-ns drift for echoes separated by 300 ns).…”

Section: Local Oscillator Stabilitymentioning

confidence: 99%

“…The stability of generating the programmable

delay is of utmost importance to the stability of the sampling rate, on which all subsequent digital processing is based. In this past publication [ 49 ], the timebase drift issue was identified: we will here demonstrate a solution to this issue by replacing a core element of the GPR receiver.…”

Section: Local Oscillator Stabilitymentioning

confidence: 99%

Acoustic Transducers as Passive Cooperative Targets for Wireless Sensing of the Sub-Surface World: Challenges of Probing with Ground Penetrating RADAR

Friedt

Martin

Goavec-Mérou

et al. 2018

Sensors

Self Cite

View full text Add to dashboard Cite

Passive wireless transducers are used as sensors, probed by a RADAR system. A simple way to separate the returning signal from the clutter is to delay the response, so that the clutter decays before the echoes are received. This can be achieved by introducing a fixed delay in the sensor design. Acoustic wave transducers are ideally suited as cooperative targets for passive, wireless sensing. The incoming electromagnetic pulse is converted into an acoustic wave, propagated on the sensor substrate surface, and reflected as an electromagnetic echo. According to a known law, the acoustic wave propagation velocity depends on the physical quantity under investigation, which is then measured as an echo delay. Both conversions between electromagnetic and acoustic waves are based on the piezoelectric property of the substrate of which the sensor is made. Investigating underground sensing, we address the problems of using GPR (Ground-Penetrating RADAR) for probing cooperative targets. The GPR is a good candidate for this application because it provides an electromagnetic source and receiver, as well as echo recording tools. Instead of designing dedicated electronics, we choose a commercially available, reliable and rugged instrument. The measurement range depends on parameters like antenna radiation pattern, radio spectrum matching between GPR and the target, antenna-sensor impedance matching and the transfer function of the target. We demonstrate measurements at depths ranging from centimeters to circa 1 m in a sandbox. In our application, clutter rejection requires delays between the emitted pulse and echoes to be longer than in the regular use of the GPR for geophysical measurements. This delay, and the accuracy needed for sensing, challenge the GPR internal time base. In the GPR units we used, the drift turns out to be incompatible with the targeted application. The available documentation of other models and brands suggests that this is a rather general limitation. We solved the problem by replacing the analog ramp generator defining the time base with a fully digital solution, whose time accuracy and stability relies on a quartz oscillator. The resulting stability is acceptable for sub-surface cooperative sensor measurement.

show abstract

“…However, for identifying subtle changes in the volume of interest, it is required to ensure a very high consistency and repeatability of the different data sets. Recently, an effective data processing procedure has been developed by Giertzuch et al (2020a) that allowed for saline tracer signal extraction in a host rock with several reflectors and fracture apertures in the sub-millimeter range.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

View full text Add to dashboard Cite

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.

show abstract

Passive Cooperative Targets for Subsurface Physical and Chemical Measurements: A Systems Perspective

Cited by 14 publications

References 21 publications

4D Tracer Flow Reconstruction in Fractured Rock through Borehole GPR Monitoring

4D Tracer Flow Reconstruction in Fractured Rock through Borehole GPR Monitoring

Acoustic Transducers as Passive Cooperative Targets for Wireless Sensing of the Sub-Surface World: Challenges of Probing with Ground Penetrating RADAR

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

Contact Info

Product

Resources

About