Application of the Full-waveform inversion Techniques to the Estimation of the Sound Velocity Structure in the Ocean

Abstract

This study investigates the effectiveness and the applicability of the full waveform inversion (FWI) method to estimate underwater sound velocity structures. We use the frequency domain full waveform inversion method in this study. In this study, the FWI is applied to the shallow-acoustic tomography first, and then we show some prospects of application to the long-range ocean acoustic tomography. We used an optimal 9 point finite difference frequency domain method for shallow acoustic tomography and the wide angled parabolic equation method for long-range acoustic tomography. We use an adjoint-state method for the calculation of the gradient in an iterative inversion based on a pre-conditioned conjugate gradient method. We first demonstrate results from a FWI method applied to a VCS experiment field data in Lake Biwa. In spite of very limited path condition using only direct arrival wave, the full waveform inversion method could describe the horizontal velocity structure possibly due to seasonal thermocline in the lake. Then, we applied the FWI method to the synthetic dataset of long-range acoustic propagation. We conclude that the FWI method could be the key success factor for the higher resolution at estimation of underwater sound velocity structure.