Projection background-oriented schlieren

A background-oriented schlieren (BOS) system is developed with two benefits over traditional BOS systems. First, the dot pattern required for BOS is projected onto a retroreflective background instead of being painted/printed onto the material itself, allowing for on-the-fly updates to the size and distribution of the dot pattern. Second, a reference image is acquired for every flow image so that real-time BOS images can be displayed, and a flow-off reference image need not be acquired if the projected dot pattern is changed during a run for BOS signal optimization. The system can be made very compact, can be converted quickly to operate as a shadowgraph system, and can be integrated with polarization optics that reduce glare/reflections from wind tunnel windows.