Viscoacoustic prestack reverse time migration based on the optimal time-space domain high-order finite-difference method

Prestack reverse time migration (RTM) is an accurate imaging method of subsurface media. The viscoacoustic prestack RTM is of practical significance because it considers the viscosity of the subsurface media. One of the steps of RTM is solving the wave equation and extrapolating the wave field forward and backward; therefore, solving accurately and efficiently the wave equation affects the imaging results and the efficiency of RTM. In this study, we use the optimal time-space domain dispersion high-order finite-difference (FD) method to solve the viscoacoustic wave equation. Dispersion analysis and numerical simulations show that the optimal time-space domain FD method is more accurate and suppresses the numerical dispersion. We use hybrid absorbing boundary conditions to handle the boundary reflection. We also use source-normalized cross-correlation imaging conditions for migration and apply Laplace filtering to remove the low-frequency noise. Numerical modeling suggests that the viscoacoustic wave equation RTM has higher imaging resolution than the acoustic wave equation RTM when the viscosity of the subsurface is considered. In addition, for the wave field extrapolation, we use the adaptive variable-length FD operator to calculate the spatial derivatives and improve the computational efficiency without compromising the accuracy of the numerical solution.