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Full-waveform inversion algorithm for interpreting crosshole radar data: a theoretical approach
Seiichiro Kuroda,Mutsuo Takeuchi,김희준 한국지질과학협의회 2007 Geosciences Journal Vol.11 No.3
Ground-penetrating radar is a useful tool for civiland environmental engineering fields because of its high resolvingpower and non-destructive measurements. This paper presents amethod of full-waveform inversion of borehole radar data forimaging permittivity structures. The inversion algorithm is basedon a conjugate gradient search for the minimum of an error func-tional relating to the difference betwen measured and predicteddata. A small model perturbation in the functional can be efficientlycalculated by propagating the data eror back into the model inreverse time and correlating the field generated by the back-prop-agation with the corresponding incident field at each point. Afinite difference time domain (FDTD) method is used for solvingMaxwells equations to obtain incident electromagnetic wavefields.Back-propagated wavefields satisfy adjoint Maxwells equations,which are stable in reverse time and can be solved by the sameconfiguration, thereby demonstrating its capability to reconstructpermittivity structures. Tests on a two-dimensional synthetic modelproduce good images of target scatterers and show stable convergence.
Hannuree Jang,Kuroda, Seiichiro,Hee Joon Kim IEEE 2011 IEEE geoscience and remote sensing letters Vol.8 No.2
<P>Cross-borehole ground-penetrating radar (GPR) has been widely used to characterize the shallow subsurface and to monitor hydrogeologic processes. To investigate an infiltration process in the vadose zone, an artificial groundwater infiltration test was conducted in Nagaoka, Japan. Time-lapse cross-borehole GPR data were collected using zero-offset profiling (ZOP) mode. The infiltration process was observed as a variation of GPR traveltimes, which can be transformed into a dielectric constant, and further converted to volumetric water content. A standard ZOP analysis, for which all first arrivals are assumed to be direct waves, results in an underestimation of the dielectric constant because of the existence of critically refracted waves. This letter presents an efficient algorithm using the maximum first-cycle amplitude to approximately determine the traveltime of direct arrival, deriving a dielectric constant model more accurately than the standard ZOP analysis from ZOP data. Tests on synthetic and real field data show that the proposed approach is effective in building accurate water content profile without iterative calculations as in the standard ZOP analysis.</P>