See the Heat

In law enforcement, specialty units normally operate at the forefront of technology. Tactical teams have used remote search cameras and night vision equipment for years, ordinance disposal teams use remotely operated robots, and vice and narcotics units use high-tech monitoring and recording equipment. Sometimes, the technology filters down into routine patrol work. Patrol officers now have computers in their cars, for example, allowing them to view NCIC records as well as the history of any individual with whom they re dealing.

Until recently, thermal imagers have been tools of the airborne, tactical and narcotics units. The thermal imager (TI), though, can provide a number of benefits to patrol officers. As increased production lowers prices and design experience increases durability, more police departments are deploying TIs in patrol operations. This article addresses some of the key benefits of TI usage on patrol.

What Is a Thermal Imager?

A thermal imager detects infrared radiation and converts it to video for you to see and interpret. Infrared radiation (IR) is what humans perceive as heat, and the TI essentially creates a heat picture of a scene. Most TIs generate an image in black and white, with black normally indicating the coldest objects and white indicating the hottest objects. The shades of gray indicate objects of intermediate temperatures. Many TIs sold in law enforcement offer reverse polarity, which means you can switch from the normal white-hot mode to a black-hot mode. In certain settings, reverse polarity can generate an image with greater clarity.

The TI functions much like the human eye. While the TI receives heat energy, the human eye receives light energy. The key is that both merely receive energy; they don t send out any beams, such as radar or a laser. Just as light passes through few materials, heat passes through few materials, and light and heat energies are transparent to different materials. While light passes through glass, clear plastics and small amounts of water (thus allowing you to see through them), for example, heat energy does not. Heat energy will, however, pass through certain plastics, thin fabrics and germanium (the element from which the lens is manufactured). As the photos above demonstrate, a TI and the human eye see the world from slightly different perspectives.

A thermal imager s ability to see without light is a key advantage of the technology for law enforcement. Even night-vision goggles require some amount of light. A suspect or object out of the range of a spotlight or flashlight may be visible on a TI if the heat signature is strong enough. Also, people know how to hide from lights, using shadows and camouflage to their advantage. But shadows and camouflage clothing do not block heat. Thus, a TI can detect people normally hidden from view.

TI History in Law Enforcement

Due to design and cost, TIs have been limited in their availability to officers, and have therefore been limited to three primary uses. First, large departments mount thermal imagers on aircraft (fixed-wing and helicopters), giving them the ability to see at night regardless of external light conditions. Airborne TIs can help track vehicles during pursuits, as well as locate fleeing suspects.

Second, tactical teams use thermal imagers in conjunction with night-vision goggles during high-risk operations. Because a TI does not require any light, it s an excellent tool to help a tactical team search a confined space, such as a basement or an attic, without exposing team members who would otherwise use flashlights.

Third, narcotics units use handheld and aircraft-mounted thermal imagers to identify indoor marijuana growing operations. While the Supreme Court s Kyllo v. U.S. ruling has placed some limits on TI usage in this application, the TI can still be a valuable tool in building probable cause for an entry search warrant.

Advances in Technology

Thermal imagers have evolved significantly over the past 10 years. Airborne thermal imagers have generally offered the best imagery, but weighing over 40 lbs., and costing more than $50,000, they have no flexibility for patrol operations. In the early 1990s, handheld TI technology was limited to delicate devices generating poor images. Two declassified military technologies leaped into the commercial spectrum, initiating a new phase in thermal imaging for public safety. The firefighting market adopted the technology rapidly, demanding that suppliers create durable, water-resistant products. Continued improvements in the core infrared technology, as well as improvements in the overall imager design by manufacturers, have led to TIs that are extremely durable, generate excellent thermal images and cost well under $15,000.

Patrol Applications

While there are a number of creative ways a patrol officer can use a thermal imager, here are the most significant applications that can make patrol work easier, safer and more effective.

Fugitive Searches

The greatest advantages in this application are at night. Most suspects understand how to use shadows and dark clothing to hide from officers at night. They may hide after escaping from custody, as a result of a foot pursuit or in preparation to commit a crime. In each case, the criminal knows how to hide from your eyesight as well as your flashlight. But most criminals don t know how to hide their heat signature.

An officer on foot can use a TI to scan any open area and gain three advantages. First, unlike a flashlight, the TI doesn t send out a beam, so criminals don t know they re being observed. Similarly, the TI doesn t reveal the officer s location, as a flashlight would. Suspects may be less cautious in trying to hide, making it even easier for the TI to detect their body heat.

Second, the TI will detect a subject hiding in the deepest shadows or wearing camouflage clothing near a hedgerow. Third, because a person s body heat travels farther than an officer s flashlight beam, the officer can locate the suspect at a greater distance in poor visibility. Example: A flashlight might be effective to 20 yards, but a TI can detect a person at more than 200 yards. Earlier detection means greater officer safety, giving the officer the opportunity to call in additional manpower or a canine unit to overwhelm and apprehend the subject.

Locating Evidence

Because a TI detects heat, officers can use it in low-visibility situations to locate evidence. After a foot pursuit, an officer could walk back along the path of the pursuit to scan the area for any unusual warm spots. Fleeing suspects would have transferred their body heat to any object in their hands or pockets, and if they tossed these items, whether packets of narcotics, a knife or a gun, they should have a latent heat signature that would show up on the TI.

Similarly, you can use thermal imagers at crime scenes to help locate all relevant evidence. Shell casings can be easier to locate with a TI than with a flashlight. (Note: Because shell casings are normally shiny brass, they may not appear hot on the thermal imager, even if recently fired. Shiny metals send artificially cold signals to the TI; as a result, they may appear as dark gray, or cold, on the TI.) The TI may locate clothing torn from a victim or suspect and lost in the bushes, especially if significant residual heat remains on the clothing. Officers could even use the TI to track a warm blood trail from a bleeding suspect or victim.

Patrol Surveillance

When the volume of dispatched calls allows, many officers engage in proactive law enforcement. This can include monitoring areas known for criminal activity, whether on a street known for drug trafficking or in an alley frequently hit by graffiti. Using a TI, you can monitor an area, witnessing hand-to-hand transactions or spotting suspicious subjects in high-crime areas. The TI s passive operation means you can perform this surveillance without announcing your position, even though the criminals believe they re operating under the cover of darkness. Patrolling large open areas such as public parks, cemeteries and parking areas is easier and more efficient as well.

Perimeter Security

When a suspect is at large and evading police, patrol officers often establish a perimeter to contain him. This allows canine, tactical or patrol officers to then search a limited area for the subject. You can establish a perimeter on two sides of a city block at the same time: Aim your cruiser s headlights and spotlights down one side of the block, and then use the TI to monitor the adjoining side. The criminal will avoid running through the bright lights guarding one side of the block, allowing you to monitor the darker side with your TI. This improves the quality of the perimeter as well as the amount of manpower required to effectively secure it.


Technological and design advances have made modern TIs small enough and durable enough for everyday use in patrol, while greater acceptance of the technology has lowered the costs. The cost of fielding a thermal imager in each beat or sector is coming down. Including thermal imagers in everyday patrol work will enhance the effectiveness of patrol officers and, more importantly, enhance officer safety by giving the patrol officer a technological advantage over the criminal element.


Jonathan Bastian is a police officer in Lexington, Ky., and a thermal-imaging specialist for Bullard. He has 14 years of experience in public safety as a firefighter, instructor and police officer.

Brad Harvey is the thermal-imaging product manager at Bullard. He has 15 years of experience in public safety as a police officer, firefighter, paramedic and instructor.

Facebook Comments



Subscribe To Our Newsletter

Join our mailing list to receive the latest news and updates from Law Officer.

You have Successfully Subscribed!