Thermal imaging applications overview for law enforcement
By Brad Harvey
Thermal Imaging Product Manager at Bullard
All objects have a certain temperature and emit waves of energy called infrared radiation. Hot objects emit more energy than cold objects. A thermal imager translates these energy waves into a viewable image, which shows a “heat picture” of a scene. Normally, a thermal imager displays hotter objects as white, cooler objects as black, and objects in between these temperatures are displayed in shades of gray. Sometimes, a thermal imager can have a reverse polarity switch that allows the user to select a black-hot mode. Because infrared radiation does not encounter many of the limitations of light, police officers can use thermal imagers to see threats or situations and objects that might normally be unseen.
Thermal imagers can assist officers at any emergency incident in which normal visibility is reduced, impaired or ineffective. Following are brief notes and graphics that describe how thermal imagers are used in a number of law enforcement applications.
While most people understand how to hide from sight, they rarely consider hiding their body heat. When ambient light, flashlights or searchlights fail to illuminate a suspect, there is still a good chance that the suspect’s body heat is visible to the thermal imager. This makes detection, tracking and apprehension easier. Additionally, since the thermal imager does not project any beam, the suspect is unaware that he is being monitored. As a result, officers can regain the upper hand against the suspect.
A thermal imager can contribute to officer safety at a number of scenes. At a collision, it could help identify fluid leaks or power lines that have been knocked to the ground. When entering a field or yard, the thermal imager can help identify fences, dogs and other hazards that may be lurking beyond the range of an officer’s flashlight. An officer could also use a thermal imager to identify people who may be hiding, or who may simply be observing in obscurity.
Because the thermal imager does not require light and only receives heat energy, it can be used to observe potential criminal activity at a distance. Whether a suspect is dealing drugs on the street, or trying to steal purses and stereos from cars, low-light conditions work to his benefit. An officer can use a thermal imager to observe the suspect from a distance, watching his activity and building further reasonable suspicion or probable cause. The thermal imagery can be recorded for use as evidence later, or merely used to justify specific interaction with the suspect.
Officers with thermal imagers can also help maintain perimeters when fleeing suspects are confined within a small area. Again, since the thermal imager emits no beams of energy, it will not alert the suspect that the perimeter is monitored, which may lead him to cross the line and be more easily apprehended.
Because the heat signature of a surface is affected by its material as well as its density, hidden compartments can be identified with a thermal imager. When the difference in density between the compartment and the surrounding surface is great, the likelihood of identifying it with the thermal imager is higher. For example, the space in a car door is normally empty. However, if the door is packed with drugs or money, its density will be different in the areas of the contraband. As a result, the thermal image will show a suspicious heat signature that can lead an officer to further investigation.
The widespread use of antilock brakes has made collision investigation more complicated. However, even when a skid mark is not visible, a rapidly stopping vehicle still generates a significant heat pattern on the roadway. Investigators can use the thermal imager to identify the direction of travel, where a vehicle left the roadway and how long the vehicle was braking. It can also be used to help locate victims, or their belongings, that may have been ejected from the vehicle.
Search and Rescue
Even though fire departments normally lead search operations, police officers may frequently arrive first or be asked to assist until sufficient manpower is on hand. Whether it is a lost child or a disoriented elderly adult, a victim can be located more quickly and at less risk with the assistance of a thermal imager. A thermal imager can overcome the normal challenges of low-light situations as well as environmental conditions, such as fog or smoke. Many thermal images will detect a human at 600 yards or more.
When earth is removed and replaced in order to hide or remove evidence, the heat signature of the ground is altered. A thermal imager can help detect areas that have been disturbed from their original state, potentially indicating where suspects may have buried evidence. Even structural changes in a wall or on a vehicle may be significant enough to be detected with a thermal imager. Patches in drywall to cover bullet holes may have a different temperature than the rest of the wall, indicating anomalies when viewed with the thermal imager. Similarly, vehicles that have undergone rapid repairs through the use of Bondo-type materials may project unique thermal signatures. This can aid in the identification of vehicles that flee collisions.
Thermal imagers are ideal in marine applications, as the open expanse of water and limited amount of heat sources makes thermal imaging easy and effective. A thermal imager can help marine officers covertly monitor an area for illegal activity, such as drug smuggling. This can also be helpful in identifying and tracking “drops” when the smuggled goods are left floating in the water for later pick-up. The heat sources of boats, personal water craft and even swimmers will be in stark contrast to the background temperatures of the water and shoreline; this makes locating, monitoring and tracking them relatively easy. A thermal imager can also help officers locate boaters and swimmers in distress, even in moderate fog.
However, a thermal imager will not see through water. It cannot identify boats, evidence or people that are completely submerged.
A thermal imager can help officers locate evidence at night, especially smaller pieces of evidence. Drugs, money and weapons thrown by a suspect during a pursuit will still retain heat from the suspect. As such, they should be easier to locate with a thermal imager once the suspect is apprehended. A thermal imager can also assist at a static crime scene, such as helping to locate shell casings and blood trails at the scene of a shooting.
Tactical Entry Teams
Tactical teams are some of the most aggressive users of thermal imaging equipment. Because the thermal imager requires no light and functions without emitting any beam of energy, it can help tactical teams maintain complete surprise over any suspects inside a building. Additionally, a thermal imager will see through the smoke and fog of chemical agents and smoke, making the entry team’s work faster, safer and easier.