This is for planefags:
Just read an article that discusses searching for underground tunnels.
"
Engineers at the MIT Lincoln Laboratory have been working on a new technology for JIDO. It includes an Airborg 10K unmanned aerial system developed by Top Flight Technologies. The platform carries an antenna and electronics payload and weighs about 15 pounds, said Christian Austin, an engineer with the lab.
If the UAS is surveying an area and it detects a large change in the magnetic field, that indicates there is something subsurface, he explained.
“It would fly around in circles and it would generate sort of a heat map of what’s in the area — what you’re seeing below the ground — or maybe it would fly lawnmower tracks [and] the output of the system would be some sort of heat map from the algorithm,” he said. A commander could then decide what action to take against any suspected tunnels.
The experimental system is currently in the demonstration phase, Austin said."
https://www.nationaldefensemagazine.org/articles/2018/1/2/going-underground-the-us-governments-hunt-for-enemy-tunnels
So has anybody noticed this sort of circling activity from drones in suspect areas?