Cameras - types

I don't know any camera that can peer underground let alone for a couple a feet. There are drones that have metal detector attachments but the Typhoon H Plus only offers photographic and thermal options.

 

Easy
Wait for a really Dry spell where crops such as grass are affected by the water content in the soil, so you see different shades of green. A lot of archaeological stone circles and burial mounds have been discovered by this method. See photo of local football pitch. The chevron markings are clay drainage pipes about a foot under the surface. Don't even have to fly just study Google Earth