All I can say is that I have flown with our deputy sheriff ( not in a helo but a piper cub they use around here ) My uncle is the Dep here and have seen cultivated plants show up well but have also seen the scan of a big pasture and seen nothing and I know for a fact it had quite a few hemp plants scattered about.. So I can only go by that and the understanding the IR is IR is IR and it only sees a heat bloom.. The bloom from a torch and a lighter is the same IR freq just one is hotter and radiates more heat. which shows up whiter .. So the plants you saw are Hotter than the surrounding area. Logic tells me its due to external sources increasing the temp of the plants you saw. Cause Plants are Cold Blooded so to speak and there would have to be a mechanism to cause a mass heat increase in a target plant.. Now if they used UV reflectivity they would be popin single plants all over the place.. Cause each living organism is UV reflective in different ranges of the UV spectrum because its such a short wave length small variables can be easily detected. Since IR wave lengths are so long the range we can detect is much narrower and we (at this time ) only detect intensity not freq range.. IMHO