Unless you can get the technology for LIDAR physically smaller in size then you are simply not going to get a LIDAR system that deep underground as some of the crawl ways and passages in certain caves barley allow a person to get through let alone bulky, fragile, expensive LIDAR equipment.
There are places in caves where it would be totally impractical, unfeasible and/ or impossible not to mention potentially life threatening to set up that kind of equipment and one of the rules about caving is that you do nothing witch is going to endanger your life or that of any one you are with; underground when you are hours away form the surface and help you need the people you are with just as much as they need you if the expedition is going to be both enjoyable and safe.
Right now the state of the art 3d mapping technology is not really suited to deep cave mapping not is the narrow often clustraphobic situations that are a common occurrence nor if your hanging on a B-Lay with a shear drop beneath you.
This means that LIDAR while you will be able to do much with it, it also means that there is going to be gaps in you data set which will have to be filled in at a latter time.
Regards to you.
Cyber-Angel