Hay here are a few more links
It is called hyperspectral optical detection
h://cannabisnews.com/news/5/thread5978.shtml
hp://www.ars.usda.gov/research/publications/publications.htm?SEQ_NO_115=123142
hp://www.gardenscure.com/420/archive/index.php/t-9652.html
Here is a good quote from the...
Growing Cannabis in the outdoors amongst otherplants visually is many times most difficult in detection even from the air. People looking for plants use a technology called Cannabis Reflection. Apparently the heat Signature from the Cannabis Plant is different from the surrounding plants...