Plane Wave Reverse Time Image for Nondestructive Tests.

Reverse time migration (RTM) has been a popular method in industry duo to its ability of imaging complex subsurface and no dip restriction. However, RTM based on full matric capture (FMC) data is limited by the time cost of the calculation and cannot be widely used. In this study, a new strategy of RTM using a plane wave is proposed. Plane wave reverse time migration (PWRTM) does not need to stack the imaging results from multiple sources and directly uses the plane wave as a source function to reconstruct the image domain, reducing the influence of numerical dispersion in PWRTM. Low-rank finite difference (LRFD) is used in wavefield simulation, the core idea of LRFD is to use the quasi differential operator to compensate the error of time steps in conventional finite difference. Mathematical derivation proves that the algorithm can be considered as analytical in homogeneous background velocity. We use the LRFD method to drive the elastic PWRTM in nondestructive testing, and the vector decomposition method is used to ensure that the phase and amplitude characteristics of the P- and S-wave are not distorted. In our simulation, compared with the scalar imaging algorithm based on the Helmholtz method, the proposed imaging algorithm can more efficiently and accurately image large angle defects.