[EE84M3i]

If they are Department of Energy, that's consistent with them not being US Military. For example, DoE is publicly known to have radiation detection helicopters - See Aerial Measuring System (AMS) and Nuclear Emergency Support Team (NEST)

[defrost]

The reason AMS like functions are carried out by fixed wing aircraft and helicopter slung pods is the weight of the doped crystal packs required to sense gamma radiation from even relatively low ground clearance.

Radiation surveys are steady paced gridding runs, evenly spaced lines flown at a uniform height and speed.

Little drones bobbing about aren't doing a good job running a detection grid.