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Tactical Uses for Thermal Imaging

Thermal imaging (TI) technology offers law enforcement officers the ability to see their surroundings in a brand new way, offering an identifiable and reliable “heat picture” of their environments. With the help of thermal imagers, officers can more effectively manage surveillance activities, locate and apprehend suspects, investigate crime scenes and conduct search-and-rescue operations.

Officers trained to use thermal imagers have a range of abilities not available with light intensification, i.e., night vision or flashlights. While thermal imagers are similar to night vision in that they assist an officer with seeing his environment, these devices work on an entirely different principle.

Light-amplification products amplify existing light, and thermal imagers detect long wave infrared, or heat. A TI detects objects and people that emit heat, regardless of light conditions, and the picture is unaffected by light, clothing or inclement weather. Typically, hotter objects show as white, cooler objects show as black, and objects between these temperatures are displayed in shades of gray.

While thermal imagers can represent a significant investment, decision-makers who have a clear understanding of the how the technology can be applied in law enforcement can more easily establish the costs vs. benefits of making such an investment. With the advent of small, handheld, rugged thermal imagers, agencies are able to move the technology from a position inside a locked case in the captain’s office to a position in the patrol car. This advancement in practicality of thermal imagers has made a significant impact on how the technology is being used on the street.

Fugitive Searches

Thermal imagers provide law enforcement officers with a unique solution for the most common problems created when officers use flashlights to search for a hidden suspect. Dark or camouflaged clothing worn by a suspect can make it very difficult for officers to use light or night-vision technology to distinguish him from his surroundings. With a thermal imager, officers have the ability to see the suspect’s body heat, which makes it very difficult for the suspect to conceal his position, whether he is hiding inside a structure or outdoors.

Thermal imagers also enable officers to conceal their positions in the process of finding and apprehending the suspect. A flashlight, on the other hand, illuminates the officer and reveals his position, showing the suspect where the officer is and where he is looking.

The Fairfield County, SC Sheriff’s Office used a thermal imager to track a suspect who had fired several rounds from a 12-gauge shotgun, then fled into the woods directly behind his residence. Under the cover of darkness, Sergeant Chris Childers approached the woods with a thermal imager and immediately identified a person standing about 40 yards into the woods.

He directed Corporal Bill Dove and Deputy Ryan Johnson, via radio commands, to where the suspect was hiding, and the man was taken into custody without incident. Childers later used the TI to identify two firearms in dense underbrush, about 10 yards from where the suspect had been hiding. Within minutes of engaging a thermal imager, both the suspect and the firearms were in custody.

Officer Safety

When officers are approaching an unknown scene, safety is a primary consideration. Whether responding to a domestic disturbance, an assault, or other potentially violent scenario, the officer is at a disadvantage with the unknowns associated with approaching the scene. With a thermal imager, an officer can stop and scan the property at a distance, identifying anyone who might be waiting outside of the residence, as well as any dogs or animals that may increase the risk involved with walking onto the property.

Surveillance Activities

Savvy criminals who know standard surveillance techniques might conceal their business by using tactics that disable light-sensing technologies. For example, drug dealers have been know to park their cars in a semi-circle, turn on the headlights and ply their trade behind the protective cover of light.

While this technique disables devices including binoculars, video cameras and night vision, it does not work with thermal imagers. Bright headlights shined directly into a thermal imager will not affect the image on the screen, so an officer with a TI can look past the headlights and see clearly what is going on. If the imager is equipped with video out, officers can record footage for evidence at trial.

Perimeter surveillance is another application in which thermal imaging can be used to dramatically improve results and reduce the time committed to a particular operation. While a flashlight can provide visibility within a short distance, a thermal imager enables one officer to monitor up to 1,500 feet or more in any direction. An added benefit to the officer operating the TI is that he can remain unseen while controlling and securing the perimeter.

Hidden Compartments

There is a common misconception that thermal imagers can see through objects such as walls. Thermal imagers do not provide X-ray vision; they only detect heat radiated from surfaces. When scanning a wall made of drywall, for example, a TI operator will be able to identify studs because the temperature of the drywall where it is in contact with the stud is different, not because the TI is seeing through the wall.

With experience, law enforcement officers can learn to use thermal imagers to detect thermal irregularities. Split fuel tanks, hollow body panels that are stuffed full, loaded tires, and even automotive body fillers and putties are identifiable under a thermal inspection. Anything that does not appear to be normal can provide a clue leading an officer to investigate further.

Accident Investigation

Traffic reconstructionists seeking to determine speed at impact often begin by measuring skid marks. Modern cars, equipped with anti-lock braking systems, are designed to not leave such marks, which makes it difficult, if not impossible, to collect this measurement on scene. When a vehicle halts rapidly, however, a significant amount of friction is created between the tire and pavement, leaving thermal signatures that can linger up to 30 minutes or longer after the collision.

Accident reconstructions at well-traveled intersections can also be made easier through the use of thermal imagers. With numerous skid marks, oil stains and grease marks, it can be difficult to tell which marks can be attributed to the accident. A thermal imager can point to the warmest marks, likely indicating those that were left most recently, yielding another piece to the puzzle of the accident. Many types of accident investigations can benefit from the use of a thermal imager. First responders in Grandview, MO, recently used a thermal imager to investigate an accident that left the vehicle wrapped around a tree in a rural area. After an unsuccessful search of nearby fields with the TI, they returned to the scene and saw a large white object in the tree immediately above the wreckage. There they found the driver, too intoxicated to flee, hiding from responding police.

Search and Rescue

While in many regions the fire department is the lead agency in searches, the reality is that police officers are often dispatched to assist. Whether the missing person is a roaming child or an elderly Alzheimer’s patient, a thermal imager can help officers search large areas in short order. Depending on the type of thermal imager used and whether there are obstacles within view, officers may be able to search up to 1,500 feet in any direction. Over clear terrain, that gives the rescuer a search circle over a half-mile in diameter.

A thermal imager eases search efforts in large fields, at parks, near roadways, and even in wooded areas. Searches near bodies of water also offer opportunities to use a thermal imager. As long as the victim is not completely submerged, his body heat should be detected by the thermal imager. By combining use of the thermal imager with the use of spotlights and flashlights, officers can search on and around bodies of water more quickly and more effectively.

Disturbed Surfaces

Every material absorbs heat and releases heat in a specific manner. Altering the material potentially changes its thermal signature, giving the thermal imager an opportunity to detect the location of any changes. Drywall that has been repaired or repainted to cover evidence will have a different thermal signature than the rest of the wall.

Recently overturned earth will change the temperature of that area and how it absorbs and releases heat. This could help an officer identify buried evidence. Body fillers and putties used in automobile repairs or to conceal compartments will heat and cool differently than the normal sheet metal, making them visible to a thermal imager.

Marine Patrol

As noted in the search-and-rescue section above, water is normally cooler than a person; therefore, a person floating on or swimming in the water appears warm and is easily visible with a thermal imager. Floating evidence, swimmers, skiers, land masses and other watercraft are all plainly visible on a TI.

Thermal imagers are generally unaffected by fog, smoke or mist common in some maritime applications. A thermal imager can be used for surveillance, navigation, watercraft enforcement or search-and-rescue operations.

Because of the limitations of infrared technology, thermal imagers do not see under water. While an officer can use the thermal imager to help locate a person or object that is above or on the surface of the water, if the person or object submerges, it becomes invisible to the thermal imager. Despite that limitation, many agencies have experienced great success using handheld thermal imagers for marine patrol.

Locating Evidence

Weapons and drugs tossed by a fleeing suspect, or even casually dropped as an officer approaches, will generally yield a latent thermal image. Officers with thermal imagers can scan the immediate area around the suspect, or the path of pursuit, to locate potential evidence.

During crime-scene investigations, the thermal imager can aid in the recovery of evidence that may be hard to detect with a flashlight and the human eye. Hotter objects, such as recently fired weapons or ejected shell casings, should generate stronger thermal images. In the above Fairfield County situation, the thermal imager not only located the armed suspect, but it also helped officers locate the weapons. This prevented the guns from being left out where children could find them, as well as providing specific evidence to contradict the suspect’s statements.

Tactical Teams

While the military has used thermal imaging for decades, the technology is still relatively new to the law enforcement community as a whole. Tactical teams are among the few specialty areas in law enforcement that have been aggressive early adopters. Whether this technology adoption arises out of an increased comfort with technology or the need to discover all reasonable advantages due to their high-risk operations, implementation of thermal imaging by tactical teams is definitely on the rise.

Thermal imaging is superior to light amplification (night vision) in that it requires no light and is completely unaffected by bright light. Camouflage, dark clothing and partial concealment can easily affect night vision, but it is rarely effective against thermal imagers. Tactical teams can use thermal imagers for a variety of applications, including pre-entry surveillance, stealth entry, search, evidence collection and even scene size-up.

While these 10 applications for thermal imaging in law enforcement are the most common, the true limits exist only in the officer’s creativity. Because of complexity, size and cost, thermal imagers have historically been safely secured in a supervisor’s office or locked away on the tactical vehicle.

This placement effectively denies the use of the thermal imager to the patrol officer, where it can clearly provide greater safety and effectiveness. As size and cost have dropped, and ease of use has improved, there are fewer reasons to keep thermal imagers out of normal patrol situations.

Brad Harvey leads law enforcement training for the Bullard Emergency Responder Division. He has 15 years of experience in public safety as a firefighter, police officer, paramedic and instructor. He can be reached at

Published in Tactical Response, Nov/Dec 2006

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