Optical flow diagnostics by background oriented schlieren methods

Abstract

Background Oriented Schlieren (BOS) methods are using the distortion of "background" - images by the light deflection due to refraction index gradients in order to obtain information about fluid density. The principal advantage of this technique in comparison to other optical density recording techniques like classical schlieren, shadowgraph, and interferometry is the modest technical equipment which is needed. In a simple realization a camera is used to image a deliberate object of sufficient texture through the phase object of interest. To perform an correlation the undisturbed image has to be taken as an additional recording or the undisturbed image is recorded otherwise. Than by the process of deconvolution a two-dimensional integral deflection map of the phase object is achieved, which is very similar to a Schlieren picture, if only the magnitude of the deflection is plotted. The technique can further be extended to Background Oriented Stereoscopic Schlieren (BOSS) and Background Oriented Optical Tomography (BOOT)