IR aerial photography film. If you like purples, you'll love this...
From Kodak's web of intrigue:
KODAK AEROCHROME III Infrared Film 1443 (DISCONTINUED) is an infrared-sensitive, false-color reversal film featuring medium resolving power and fine grain.
Richard Mosse has a large body of work using this.
I am wondering about that red filter given the IR characteristics of the film.