Full-scale High-speed “edgerton” Retroreflective Shadowgraphy of Explosions and Gunshots
نویسندگان
چکیده
Almost 1⁄2 century ago, H. E. “Doc” Edgerton demonstrated a simple and elegant directshadowgraph technique for imaging large-scale events like explosions and gunshots. Only a retroreflective screen, flashlamp illumination, and an ordinary view camera were required. Retroreflective screens have been used for shadowgraphy in the interim, but the unique combination of large-scale, simplicity and portability offered by this approach has barely been tapped. In particular, Edgerton’s retroreflective shadowgraph is available for use in applications hostile to most optical diagnostics, such as full-scale outdoor daylight field testing of explosives and weapons, and homeland security research. Also in the interim different retroreflective materials have appeared, though 3M’s ScotchliteTM brand is still among the best. In particular, though, digital high-speed cameras are rapidly replacing the older film-camera technology. Here we have used a 2.4 m square retroreflective screen and continuous point-source illumination from a powerful xenon arc lamp. The lamp casts a shadowgram on the screen that is recorded at 1 μs frame exposure and at various frame rates and resolutions using a Photron APX CMOS digital camera. Examples are shown of an explosion and the discharge of several different firearms. The ability to quickly and easily acquire high-speed digital shadowgraph movies in hostile environments is especially helpful in visualizing the time-dependent physics of such complicated events as those examined here.
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