A novel approach for reconstructing water surface using shape from shading technique

Abstract

Imaging based techniques provide for a way for reconstructing surfaces using Shape from shading algorithms. Adding the convenient approximation of target wave fields by superposition of simple plane waves a new greedy algorithm for reconstruction of water surface is introduced. The algorithm developed optimizes each wave-front for several parameters until the least squares error is minimum. The methodology is illustrated by application to synthetic and real data obtained from the experiments performed in Linear wave lab at Embry Riddle Aeronautical University (ERAU). Generalization of approach to non-linear problem of reconstructing water waves from reflectance data modeled by Lambertian reflectance model is demonstrated. Possible improvements including use of Specular reflection model and better optimization techniques are discussed. The approach is observed to be an effective way for reconstructing any kind of water wave field.

Comparison of Schlieren-based techniques for measurements of a turbulent and wavy free surface

“…We induce the rough surface topography through a submerged jet angled towards the free surface, as well as by generating a random wavefield from an emergent jet overspill. This is in contrast with a majority of the previous water surface reconstruction exercises, where nearlyperiodic and uniform waves/wave-like structures are observed (Chaudhari et al, 2014;Jain, 2020;Moisy et al, 2009;Wildeman, 2018). Consequently, our analysis sheds new insight into (1) the hydrodynamics of a random wavefield that is induced by a collapsing vertical jet and (2) the turbulent manifestation of a submerged free-shear flow on a free surface and the resulting surface crispation.…”

“…This method was labelled 'free-surface synthetic Schlieren' (FS-SS) and has since been used for various applications (Li et al, 2021;Mandel et al, 2017Mandel et al, , 2019Paquier et al, 2015;Pathommapas et al, 2019;Wildeman, 2018). Shape from shading (SFS) has also been used for the reconstruction of water surfaces, wherein the gradual variation in shading is used to recover the shape of the features of interest (Chaudhari et al, 2014;Nie et al, 2021;Pickup et al, 2011).…”