Believe it or not, the structure profile is probably the oldest and most common law enforcement application for a handheld thermal imager. It is also the most challenging application, due to a questionable Supreme Court ruling. However, the general notion is that you can use a thermal imager to help identify the presence of an indoor marijuana grow.
The Indoor Challenge
Growing plants indoors is not new, nor difficult. By bringing the soil inside (in a planter), regularly watering the plant, and allowing natural sunlight into the room, you can grow almost anything inside. The problem with growing marijuana inside, however, is that it's illegal (it's illegal outdoors too, but you get the point). And growers are greedy. Since it is illegal, they cannot grow plants near windows. Since they are greedy, they are not happy with just four or five plants.
Therein lays the pot grower's conundrum. He needs light, but cannot use natural light. Therefore, he has to use artificial light that simulates sunlight. Besides the tremendous amount of electricity this requires, it generates an overwhelming amount of heat. This is problematic for the grower, as marijuana does not grow well in hot environments.
So, the pot grower has to vent this excess heat somewhere outside the pot growing room. The greedier he is, the more plants he grows. The more plants he grows, the more lights he needs. The more lights he needs, the more heat he generates. The more heat he has, the more he has to vent. And, since the thermal imager sees heat...it can be a great tool to locate abnormal heat signatures on and around buildings.
By comparing a suspect structure to similar structures, you might see unusual heat build-up that indicates a grow room. Or, you might see strange heat patterns indicating the location and direction of vents. Either way, it can be another indicator in your investigation that the suspect is indeed growing marijuana.
Up until 2001, police officers could use a thermal imager to scan any home, farm, office, shed or other structure at their whim. Obviously, good police work dictates building sufficient probable cause to get an arrest or search warrant. Not only is it unethical, but it would also be a waste of time and effort to scan homes and buildings at random, just hoping to find odd heat patterns. As an investigator, you need to put in the time and effort to do things the proper way. The TI is not a shortcut to a good investigation; it's just a tool to help generate another piece of evidence.
That said, 2001 changed the thermal imaging landscape in the US. Erroneously stating that thermal imaging was a technology not available to the general public, and concerned that some unknown future technology might make it possible to see the intimate details of private life within the confines of a home's four walls, the Supreme Court banned a current technology that does not reveal the intimate details within a home.
Catch that? Yep, worried about something that does not yet exist that could see into a home, the justices decided to restrict a technology that does exist but does not see into a home. So, courtesy of Kyllo v. U.S., police officers must now obtain a search warrant prior to performing a thermal scan of a private dwelling. Notice, the Kyllo decision applies only to private dwellings, where the expectation of privacy is highest.
Now, some jurisdictions have required thermal search warrants for years. Some may now stretch the Kyllo decision to include businesses, outbuildings and the like. But as far as the U.S. Supreme Court cares, the warrant restriction applies only to scans of dwellings.
Ethical Use on Structures
As mentioned above, randomly scanning buildings to find a suspicious heat signature is wrong and a waste of resources. But once you have initiated a proper investigation into a suspect building, the TI can be part of the evidence you collect to prove your case.