> Where is the camera relative to these target aircraft, and what's behind them?

Straight from [NASA themselves][1]:

> NASA flew a B-200, outfitted with an updated imaging system, at around 30,000 feet while the pair of T-38s were required to not only remain in formation, but to fly at supersonic speeds at the precise moment they were directly beneath the B-200

[and][2]

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


  [1]: https://www.nasa.gov/centers/armstrong/features/supersonic-shockwave-interaction.html
  [2]: https://www.youtube.com/watch?v=NZPK3B8rQV4
  [3]: https://i.sstatic.net/ySI8K.png