Pictured is an example of an image produced using the Krypton Tagging Velocimetry technique used to measure velocity in a hypersonic wind tunnel such as Arnold Engineering Development Complex Wind Tunnel 9. The single “write line” in the image is the initial fluorescence created by a laser pulse “pumped” into a wind tunnel filled with Krypton gas (~1% seeding in volume). The multiple “read lines” show the dissolution of the write line over time. (U.S. Air Force photo)