Schlieren imaging reveals shock waves due to the air density gradient and the accompanying change in refractive index.
This schlieren image above dramatically displays the shock wave of a supersonic jet flying over the Mojave Desert.
Researchers used NASA-developed image processing software to remove the desert background, then combined and averaged multiple frames to produce a clear picture of the shock waves.
There’s more information about how the system works on the NASA website.

Bill Condie
Bill Condie is a science journalist based in Adelaide, Australia.
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