As one of the cops involved in detecting and eradicating dope, I can tell you that thermal imaging is not used much for outdoor grows.
In the early 1990's when peace broke out, the DoD and other agnecies with hi-tech equipment that was suddenly under-used came to law enforcement and touted their wares. We tried everything from computer analyzed, false color photography, IR, and thermal imagining. None of them were very effective on outdoor grows.
Thermal imaging is still VERY BIG with indoor grows because of the heat generated by the cultivation.
Infra red (IR) and thermal gear worked best on outdoor grows when used during the heat of the day. The water lines, being cooler, than the surrounding terrain and vegatation show up very well, but there was no way to tell if they were domestic water supply or supporting a grow.
Perhaps the most insidious use of this spy technology was the attempts to use sensitive equipment to detect the minute amounts of radio isotopes in the galvanized chicken wire and the low level electrical impulses put out by batteries in the water timers. These happened at a level much higher than my lowly position so I don't know if they had any success.
