If you have ever heard a clap of thunder, the boom of fireworks, or the roar of a supersonic jet, you already know how shock waves sound. Now a team of NASA researchers has generated images that show how the remarkable waves look.
The team used a modern version of a 150-year-old German photography technique called Schlieren imaging to show shock waves streaming from jets flying at supersonic speeds. Shock waves are narrow regions of air where pressure, temperature, and density characteristics are drastically different than surrounding areas. Shock waves occur when objects move faster than the speed of sound, which is 1,236 kilometers (768 miles) per hour.
In the top image, shockwave structures are visible behind a T-38 jet passing in front of the Sun (which gets its purple color from a calcium-K optical filter). Shock waves appear darker because changes in the air density affect how much light is refracted. The bright and dark splotches on the Sun’s surface are sunspots—areas that are slightly cooler but more magnetically active than the rest of the Sun’s surface. The camera that captured this image was located on the ground.
The second image shows shock waves produced by a supersonic jet flying over the Mojave Desert. The image was captured by a high-speed camera on the underside of a smaller aircraft flying several thousand feet above the jet.
Specialized image-processing techniques were required to produce the images. Researchers first collected a series of photographs on a speckled background pattern. They then used computer algorithms and image processing software to deduce the locations of the shock waves based on distortions of the background pattern—an approach called the background-oriented schlieren technique.
While either the land surface or the Sun can serve as the background, using a celestial body is simpler and cheaper because the camera can be located on the ground rather than on a second airplane.
- Amateur Spaceflight Association Shock Wave Basics. Accessed October 6, 2015.
- NASA (2015, September 23) Ground-Based Schlieren Technique Looks to the Sun and Moon. Accessed October 6, 2015.
- NASA (2015, August 25) Schlieren Images Reveal Supersonic Shock Waves. Accessed October 6, 2015.
- Weinstein, L. Visualization and image processing of aircraft shock wave structures. Accessed October 6, 2015.
Imagery courtesy of the Calcium-K Eclipse Background Oriented Schlieren (CaKEBOS) team. Caption by Adam Voiland.