Full waveform inversion algorithm for interpreting cross‐borehole GPR data

Abstract

The time‐domain electromagnetic (EM) method such as ground‐penetrating radar is a useful tool for civil and environmental engineering fields because of its high resolving power and non‐destructive measurements. This paper presents the full‐waveform inversion of EM wavefield data for imaging the cross‐borehole permittivity structure. The EM full‐waveform inversion method uses the conjugate gradient method to minimize an objective function. Frechet derivatives can be calculated by the crosscorrelation at zero lag between the forward propagated wavefield and the backward propagated wavefiled represented by the adjoint Maxwell's equations. Both the forward and backward propagations are calculated by a same stable finite difference time domain method. The inversion algorithm is validated using a synthetic model having non‐uniform permittivity distribution.