Special Agent Ed Wall
Wisconsin Department Of Justice
Division of Criminal Investigation

As the pressure from law enforcement on outdoor cannabis cultivators has gradually increased over the years, so has the grower’s ingenuity in concealing their illicit activity. Several years ago the discovery of large fields of marijuana was fairly common. Those days are gone. The trend over the last decade has been toward sophisticated indoor grows and smaller, well concealed outdoor sites. Unfortunately, in reviewing the statistics for law enforcement’s discovery of indoor and outdoor grows, we find that the success rate has gradually dropped.

The investigation of outdoor grows has become very difficult with the advent of the experienced growers sharing their knowledge by way of publications and the internet. Historically, one of the best ways to detect outdoor marijuana grows has been through the use of aerial assets such as helicopters, fixed wing aircraft and the National Guard C-26 Counter Drug aircraft.

Daytime surveillance in attempting to locate the illicit marijuana grow has been limited to eye sight with occasional enhancements such as binoculars or video cameras equipped with zoom capability. The deficiency in eye sight is that the camouflage utilized by the grower can easily defeat even the best equipment and most experienced observers.

The law enforcement officers responsible for locating illicit outdoor marijuana grows should consider use of a thermal imager during daylight conditions from an aerial platform to locate marijuana plants.

When viewed from the ground, an overgrown field or sparsely wooded area can easily conceal plants by virtue of vegetation and natural contours of the land. When viewed from the air with the naked eye, the observer’s ability to distinguish individual plants is somewhat enhanced, but still very difficult.

As an example we will consider the aerial view of an overgrown farm field with several marijuana plants among the weeds, tall grass, tree saplings etc.. When that field is viewed with a thermal imager during daylight, the individual plant locations become very evident. Not because the plants themselves are observable, but because the ground has been altered in planting them.

The ground around the plants is turned and the vegetation around the immediate base of the plants is generally trimmed away. This allows water and nutrients to penetrate the roots and keeps weeds from undermining the plants ability to thrive. When the illicit marijuana grower alters the uniformity of the soil compaction and clears the vegetation shading the base of the plants, they have inadvertently created a favorable condition for discovery by law enforcement using a thermal imager.

The lack of shading that had been provided by cleared ground cover and the turned soil causes the sun’s heat to be absorbed at a higher rate than the other ground immediately surrounding the plants. That change in heat absorption causes the plant locations to emit a much higher ambient heat picture and enables the officers to direct ground units to the suspected area.

As the marijuana grow season approaches, law enforcement begins to gear up for another summer thrashing around in search of illicit activity. Take the time to include a daytime aerial thermal image mission in your next outdoor grow case. It may be the difference between pulling plants and just another walk in the woods. Good luck and be careful.