Guldström - Ground-penetrating radar (GPR) with Drone. If you are serious about metal detecting you will need this, best thing is that is is not a Joke and it is "Made in
USGS Tests drone-based ground-penetrating radar for bathymetry | U.S. Geological Survey
Drone for Subsurface Inspection - Nordic Unmanned
See through the surface of ground, ice or any structure with a drone equipped with Ground Penetrating Radar (GPR) – sUAS News – The Business of Drones