High-Resolution Background-Oriented Schlieren Technique for a Laser-Induced Underwater Shock Wave

Background-oriented schlieren (BOS) technique is a nonintrusive method to obtain global pressure field via refraction of light induced by the density change in fluid. Although the cross-correlation method so-called PIV-BOS is commonly used for computing the displacement field, this method induces to decrease the accuracy of the pressure field due to poor spatial resolution. In order to improve the spatial resolution, we apply the optical flow to computation of displacement field. The pressure field of a laser-induced underwater shock wave is used to validate the techniques. We show that the profile of shock wave is successfully captured by the optical-flow-based BOS (OF-BOS). Poor spatial resolution of pass-integrated displacement field deteriorates the accuracy of three-dimensional reconstruction.