"Schlieren" imagery, invented in 1864 by German physicist August Toepler, has the ability to reveal shock waves created by supersonic aircraft thanks to air density gradient and a visible change in what is called the refractive index of air - or the speed of light in a given medium.
"This typically requires the use of fairly complex optics and a bright light source, and until recently most of the available schlieren imagery of airplanes was obtained from scale model testing in wind tunnels," Nasa said.
"Acquiring schlieren images of an aircraft in flight is much more challenging. Ground-based systems, using the sun as a light source, have produced good results but because of the distances involved did not have the desired spatial resolution to resolve small-scale shock structures near the aircraft."
By using Nasa-developed software, researchers were able to remove the desert background from the images, then combined and averaged multiple frames for a clear picture of the shock waves.
The results will help engineers to design a quiet supersonic transport.
There are regulations stopping unrestricted overland supersonic flights in the US, with planes producing a sonic boom over populated areas being viewed as the principal barrier to future supersonic civil aviation.
Researchers believe a clear understanding of the location and relative strength of the shock waves is essential for designing a high-speed commercial aircraft that fits within these regulations.
"It is hoped that the ... images can be used to validate or improve current design techniques," said Brett Pauer, commercial supersonic technology manager at Armstrong. Staff reporter
