Reverse-time migration and full wavefrom inversion for subsurface imaging

Abstract

This paper presents a multi-input and multi-output (MIMO) ground penetrating radar (GPR) system, for imaging shallow regolith structures and estimating the dielectric properties. Both reverse-time migration (RTM) algorithm and full waveform inversion (FWI) algorithm are applied for subsurface imaging. The reverse-time migration algorithm is developed to process the MIMO GPR dataset for obtaining a high-resolution image of the subsurface objects. In reality, RTM is preferred to be implemented in the computationally attractive 2D domain, since 3D forward modeling is time consuming. This implies a infinite line source is desired, other than a point source in the 3D case. We adopt a frequency-domain filter algorithm to correct for this amplittude difference and the associated phase shift by transforming the recorded 3D field data to approximate 2D equivalent. The results of a laboratory experiment on a volcanic ash pit demonstrate that the upper and lower interfaces of a marble slab of 3 cm thickness buried at a depth up to 2m can be clearly imaged. The stabilized bi-conjugate gradient stabilized method fast fourier transform (BCGS-FFT) is employed in the forward scattering calculation, and the full waveform inversion algorithm based on distorted Born iterative method (DBIM) is used to retireve the dielectric properties of the subsurface objects. The preliminary results of a numerical experiment demonstrate that the dielectric permittivity of a subsurface cubic object can be accurately obtained using the MIMO GPR dataset at only six discrete frequencies.