These two popular press articles discuss the use of schlieren photography to image shock waves of jets during flight using a special schlieren camera in a chase plane.

 - Gizmodo: [NASA Captures First-Ever Images of Intersecting Shockwaves From Two Supersonic Jets](https://gizmodo.com/nasa-captures-first-ever-images-of-intersecting-shockwa-1833103849)
 - Ars Technica: [NASA visualizes supersonic shockwaves in a new, awe-inspiring way](https://arstechnica.com/science/2019/03/nasa-visualizes-supersonic-shockwaves-in-a-new-awe-inspiring-way/)

NASA's Glenn Research Center page [Schlieren photography](https://www.grc.nasa.gov/www/k-12/airplane/tunvschlrn.html) is instructive but doesn't give a clue how this is done from another plane. What takes the place of a special light source in this situation?

[![NASA intersecting shock waves][1]][1]

[![NASA Schlieren photography][2]][2]

[![enter image description here][3]][3]


  [1]: https://i.sstatic.net/RYKN9.jpg
  [2]: https://i.sstatic.net/RmylS.jpg
  [3]: https://i.sstatic.net/b7VDA.jpg