Automatic Differentiation‐Based Full Waveform Inversion With Flexible Workflows

Abstract

Full waveform inversion (FWI) is able to construct high‐resolution subsurface models by iteratively minimizing discrepancies between observed and simulated seismic data. However, its implementation can be rather involved for complex wave equations, objective functions, or regularization. Recently, automatic differentiation (AD) has proven to be effective in simplifying solutions of various inverse problems, including FWI. In this study, we present an open‐source AD‐based FWI framework (ADFWI), which is designed to simplify the design, development, and evaluation of novel approaches in FWI with flexibility. The AD‐based framework not only includes forword modeling and associated gradient computations for wave equations in various types of media from isotropic acoustic to vertically or horizontally transverse isotropic elastic, but also incorporates a suite of objective functions, regularization techniques, and optimization algorithms. By leveraging state‐of‐the‐art AD, objective functions such as soft dynamic time warping and Wasserstein distance, which are difficult to apply in traditional FWI are also easily integrated into ADFWI. In addition, ADFWI is integrated with deep learning for implicit model reparameterization via neural networks, which not only introduces learned regularization but also allows rapid estimation of uncertainty through dropout. To manage high memory demands in large‐scale inversion associated with AD, the proposed framework adopts strategies such as mini‐batch and checkpointing. Through tests on synthetic and field data, we demonstrate the novelty, practicality and robustness of ADFWI, which can be used to address challenges in FWI and as a workbench for prompt experiments and development of new inversion strategies.Characterization of the Earth's subsurface is crucial for oil exploration, earthquake studies, environmental assessments, etc. Full waveform inversion (FWI) is a technique that helps scientists create detailed images of the subsurface by comparing observed with simulated seismic data and adjusting the Earth model accordingly. This study introduces ADFWI, an open‐source framework dedicated to simplifying FWI with automatic differentiation, which is a technique widely used today in machine learning and inverse problems. ADFWI largely simplifies the use of advanced mathematical techniques and numerical implementations, rendering it easier for researchers to develop and evaluate new approaches in FWI to imaging different subsurface formations. The framework supports a wide range of wave equations in different media and optimization methods, and allows comparisons of different strategies efficiently. Integration of ADFWI with deep learning can further improve inversion stability and expedite uncertainty assessments. Overall, comprehensive evaluations on synthetic models and field data show that ADFWI is reliable and user‐friendly, and is useful for researchers to tackle challenges in obtaining complex subsurface structures. ADFWI, an automatic differentiation‐based, open‐source framework, offers an alternative to the adjoint state method (ASM) in Full waveform inversion (FWI) The framework integrates various wave equations, objectives, and regularization methods, allowing fast uncertainty estimation using dropout With efficient memory management using mini‐batches and checkpointing, ADFWI is practical for large‐scale FWI