Orateur
Description
The free-surface Synthetic Schlieren (FS-SS) method, originally proposed by Moisy et al. (2009), is a high-resolution, refraction-based optical technique used to measure the instantaneous elevation of liquid interfaces. Traditional FS-SS typically relies on three approximations — small paraxial angles, small slopes and small amplitudes — to establish a linear relationship between the gradient of the surface elevation and the apparent displacement field of a refracted pattern imaged through the surface. In this work, we propose three nonlinear extensions of the FS-SS method specifically designed for telecentric imaging systems. By leveraging a telecentric lens to eliminate paraxial distortions, we simplify the optical model and derive a hierarchy of nonlinear free-surface reconstruction algorithms. These schemes progressively incorporate higher-order refraction terms and depth dependent corrections, extending the validity of FS-SS into regimes characterized by large amplitude-to-depth ratios and steep surface gradients. Notably, these advancements are achieved at a low computational cost, requiring only a few iterations to converge.