Time-dispersion correction for arbitrary even-order Lax-Wendroff methods and the application on full-waveform inversion

Abstract

A second-order accurate finite-difference (FD) approximation is commonly used to approximate the second-order time derivative of a wave equation. The second-order accurate FD scheme may introduce time dispersion in wavefield extrapolation. Lax-Wendroff methods can suppress such dispersion by replacing the high-order time FD error terms with space FD error-correcting terms. However, the time dispersion cannot be completely eliminated and the computation cost dramatically increases with increasing order of (temporal) accuracy. To mitigate the problem, we have extended the existing time-dispersion correction scheme for the second- or fourth-order Lax-Wendroff method to a scheme for arbitrary even-order methods, which uses the forward and inverse time-dispersion transform (FTDT and ITDT) to add and remove the time dispersion from synthetic data. We test the correction scheme using a homogeneous model and the Sigsbee2A model. The modeling examples suggest that the use of derived FTDT and ITDT pairs on high-order Lax-Wendroff methods can effectively remove time-dispersion errors from high-frequency waves while using longer time steps than allowed in low-order Lax-Wendroff methods. We investigate the influence of the time dispersion on full-waveform inversion (FWI) and show an antidispersion workflow. We apply the FTDT to source terms and recorded traces before inversion, resulting in the source and adjoint wavefields containing equal time dispersion from source-side wave propagation and the modeled and observed traces accumulating equal time dispersion from source- and receiver-side wave propagation. The inversion results reveal that the antidispersion workflow is capable of increasing the accuracy of FWI for arbitrary even-order Lax-Wendroff methods. In addition, the high-order method can obtain better inversion results compared to the second-order method with the same antidispersion workflow.