Flying a raster pattern with a detector over the landscape; I bet the real money is in undiscovered pallasites, not ancient submerged anchors or cannon. And, go get a shovel, no need for rental marine salvage ships. How many multi-ton nickel- iron meteorites are sitting out there in wilderness, a couple meters deep?
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Everyone [search "OPM," latest cool magnetometer,][1] like a SQUID but no cryo required, nor heavy shielding. Laser plus rubidium vapor beats proton precession or Overhauser.
But nobody has yet built a DIY hobbyist OPM instrument. How far below a hexacopter must your magnetometer dangle, to avoid motor amps and stator magnets?!
Yes, this means [Christopher Walken's helmet from Brainstorm (1983)][2] doesn't need liquid helium vapor jets anymore.
[1]:(((((((((((((((((( ( ( ( ( (O) ) ) ) ) ))))))))))))))))))) William J. Beaty SCIENCE HOBBYIST website billb amasci com