Self-Nulling Schlieren Imaging for Aircraft in Flight

Schlieren imaging is an especially useful tool for studying shock waves created by aircraft, because shock waves create strong refractive index gradients that can be visualized. Until recently, the large and delicate instrumentation required for schlieren photography mostly restricted the technique's use to ground test facilities. Previous work has shown that full-scale schlieren images of an aircraft in flight can be synthesized by analyzing high-speed video of the aircraft flying across the sun. The solar schlieren method is especially useful for air-to-air schlieren photography, because an airborne observation platform provides a unique perspective view of the second aircraft. We propose to advance this technique via a new self-nulling schlieren imaging method which has the potential to substantially increase the sensitivity of the technique. This technology could be also used to study large-scale aerodynamic problems where conventional laboratory schlieren imaging is impossible.