I've heard of drones being used in mines to survey old/abandoned mines. Not sure how they are pushing the drones deep into the mine system and BLOS. Would an acoustic (beacon) system work similar to what a Roomba uses to find home in a large house? They could be dropped/staged along the way as the drone pushes farther in with each flight? I'd like to know more as my buddy and I want to explore a few cave systems out west using Phantoms and Mavics this summer. Any suggestions on where to go online to get started with the research? Also, is there a 'direct line' to DJI engineering to bounce ideas such as this and discuss the use/limitations of Lightbridge in these underground scenarios? Thanks!