Schlieren imaging was developed in the 1800s to detect flaws or schliere in glass. The technique is frequently used today as a means of visualising shock waves in wind-tunnels and temperature gradients around objects.

Schlieren imaging relies on the refractive index (the ability to bend light) of a transparent medium (often air) changing with density to produce an image. In a simple schlieren system a parallel beam of light is passed through the subject and is focussed on to a knife edge using lenses or spherical mirrors.

A change in density in part of the subject causes that part of the light beam to be refracted and to fall above or below the knife edge creating lighter or darker areas in the image. Colour filters are sometimes used in place of a knife edge to produce an image using different colours to denote different areas of density.


- Shock Physics
- Combustion Research
- Wind-tunnel Research
- Flow Visualisation
- Thermodynamics
- Ballistics