NASA is using a 21st century version of schlieren imagery, invented in 1864 by German physicist August Toepler, to visualize supersonic flow phenomena with full-scale aircraft in flight. Schlieren imaging reveals shock waves due to air density gradient and the accompanying change in refractive index. This classically required the use of fairly complex optics and a bright light source. Recently, synthetic schlieren techniques have been developed based on image processing methods. Background oriented schlieren (BOS) has been a particularly successful method. First, researchers obtain an image of a speckled background pattern. Next, they collect a series of images of an object in supersonic flow in front of the same pattern. Shock waves are deduced from distortions of the background pattern resulting from the change in refractive index due to density gradients. This method requires very simple optics and a variety of background patterns, including natural ones, may be used.