Velocity and Density Reconstruction Based on Scattering Angle Separation

The density of the medium under investigation is important for seismic interpretation and rock property analysis. However accurate estimation of density is difficult, because seismic responses to density and velocity are coupled, and there exits a trade-off problem. By analyzing the properties of their radiation patterns, we propose a scattering angle-based inversion strategy for simultaneous estimation of density and velocity. Both the source-side and receiver-side wavefields are decomposed into local angle domain, and then local scattering angles are calculated. Small scattering angles correspond to forward scattering, which are caused by velocity perturbation, so small scattering angles are used only for velocity estimation. Density perturbation is only responsible for backward scattering, which are related to large scattering angles. Therefore by filtering out small scattering angles during density inversion, the crosstalk between velocity and density is greatly reduced. Numerical examples prove that the scattering angle-based inversion method provides much improved density inversion results. Furthermore, the multi-stage strategy also helps velocity to overcome the cycle skipping problem in highly nonlinear full waveform inversion.