Truncated Gauss-Newton Method with a Modified Scattering-integral Approach for Multi-parameter FWI in Acoustic Media

Density is difficult to reconstruct in multi-parameter full waveform inversion, due to the cross-talk effects between velocity and density. In this study, we implement the truncated Gauss-Newton method to multi-parameter FWI in acoustic media, in which we incorporate the inverse of the approximate Hessian where the off-diagonal blocks reflect the trade-off effects between different parameters, to decouple the velocity and density during the reconstruction procedure. The model update is computed through the matrix-free conjugate gradient (CG) solution of the Newton linear system. We adopt a modified scattering-integral approach to calculate the gradient of the misfit function with respect to the model parameters and the Hessian-vector product instead of the widely accepted adjoint-state method. The numerical examples prove the feasibility of our method.