>In other words, they can see what the drone sees, pulling out their recognizable pattern from the radio signal, even without breaking the drone's encrypted video. The most interesting part of this is how encrypted traffic leaks enough info to be reliably analyzed. Really cool stuff.
The key insight is that the drone should store the video to local storage for later (1) recovery or (2) buffered encrypted transmission to the mother ship which would eliminate the leakage of clues about what subject is being spied upon.
Granted, you could obfuscate things by varying the buffer length and padding the data stream (as suggested near the end of the article) - but at some point, a high-value surveillance target will probably just assume that a nearby drone is probably not operated by an avid bird-watcher or something like that and just blast the drone out of the sky. (Preferably using a laser or better still lots and lots of microwave RF - tends to get the surroundings less aggravated than using a shotgun...)