Detection of Tracer Plumes Using Full‐Waveform Inversion of Time‐Lapse Ground Penetrating Radar Data: A Numerical Study in a High‐Resolution Aquifer Model. Issue 5 (9th May 2022)

• Record Type: Journal Article
• Authors: Haruzi, P.; Schmäck, J.; Zhou, Z.; van der Kruk, J.; Vereecken, H.; Vanderborght, J.; Klotzsche, A.
• Is Part Of: Water resources research. Volume 58:Issue 5(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-05-09
• Subjects: hydrogeophysics -- GPR -- full‐waveform inversion -- time‐lapse -- tracer experiment -- petrophysical relations -- transport modeling; Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2021WR030110
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: Imaging subsurface small‐scale features and monitoring transport of tracer plumes at a fine resolution is of interest to characterize transport processes in aquifers. Full‐waveform inversion (FWI) of crosshole ground penetrating radar (GPR) measurements enables aquifer characterization at decimeter‐scale resolution. The method produces images of both relative dielectric permittivity ( ε r ) and bulk electrical conductivity ( σ b ) that can be related to hydraulic aquifer properties and tracer distributions. To test the potential of time‐lapse GPR FWI for imaging tracer plumes, we conducted a numerical tracer experiment by injecting saline water, desalinated water, and ethanol in a heterogeneous aquifer. The saline and desalinated tracers only changed σ b, whereas ethanol changed both ε r and σ b . Tracer concentrations were retrieved from the inverted ε r and σ b models using information about petrophysical parameters. GPR FWI ε r and σ b tracer images could recover preferential paths of ∼0.2 m width, while the derived σ b structures are smoother. FWI of 50 time‐lapse data sets demonstrated the potential of the FWI to derive spatially resolved breakthrough curves of the saline and ethanol tracer in the image plane between the boreholes. Thus, high‐resolution imaging with GPR FWI of tracers that produce a high permittivity contrast against the background has a great potential for characterization of heterogeneous transport in aquifers. Key Points: Time‐lapse crosshole ground penetrating radar (GPR) full‐waveform inversion (FWI) shows a potential to monitor high‐resolution of ∼0.2 m transport of tracer in aquifer Starting model strategies for FWI were tested in order to optimize plume reconstruction, to be used later for field data sets Good recovery of conductivity and especially of permittivity changes suggests to monitor adequate tracers by GPR FWI for transport imaging