How do helicopters detect marijuana?

Law Enforcement utilize thermal imaging scopes mounted on helicopters to detect outdoor marijuana crops. Realizing that cannabis growers tend to plant their crop interspersed with other species for camouflage, they rely on the heat reflectivity of cannabis to distinguish it from surrounding vegetation. Some growers plant their cannabis near conifers (spruce, pine, fir, or coniferous shrubs) in order to mask the heat signature of their plants with that of the larger trees. If this is not an option (or is not practical) I would recommend wide spacing between plants laid out in a very random pattern. If plants are small (indica or sativa-indica hybrid) then two or three can be grouped together in small patches, the larger the patch of cannabis, the more the risk of detection. If plants are large (sativa dominant) they should be arranged as far apart as possible and obscured by native ground cover. If all else fails, a few .223 rounds through their fuselage should convince them to look elsewhere for someone to oppress (just kidding, don't give the police any justification for their fascist persecution of non-violent growers).