Thermal imaging does not really spot weed plants in the thick woods. If you look through an infrared camera at a spot in the woods with with manzanita, oak, pine, some brush, and marijuana, the weed won't even stick out. Its not like the weed plants are glowing red while everything else is blue lol. As far as visibly spotting, it is very hard, if not impossible, for a helicopter to spot single weed plants like 8 feet apart in the brush. As long as they are not 10 foot monsters you should be fine