>> they would leave big airplane-shaped objects on the tarmac to create cold spots for Soviets' spy satellites to photograph in infrared, corresponding to planes that didn't exist.

You're referring to project OXCART which preceded the Blackbird program. The documentary you're referring to was called "Area 51 Declassified" which was on National Geographic channel:

https://youtu.be/fE8xqTO6hXk

It's a fascinating documentary