It's a dreary winter night, and you can't see your own hand through the fog, let alone the car thief you've been tailing for the past two miles. You think you see his taillights move over to the side of the road and you swerve over to the shoulder.

You park alongside the car you've been chasing, but your perp is nowhere to be seen. He might have run into the thick woods that cover this area. Or he could be hiding in one of the few houses nearby. Backup officers show up and together you contemplate your next move. You wish you could cut through the fog and darkness to nab the guy. If only you had a thermal imaging camera...

What is Thermal Imaging?

The technology known as thermal imaging senses heat using infrared—a part of the light spectrum the unaided human eye cannot see—and displays it on a screen as images in varying shades of gray. But perhaps it's easier to describe it by explaining what it's not.

Don't Call it Night Vision

If you call thermal imaging night vision, you won't just perturb manufacturers of equipment that use the two technologies, you just might request the wrong equipment for your mission.

Although it may seem that thermal imaging and night vision are the same thing, they perform very different functions.

Thermal imaging detects heat, while night vision magnifies light.

Night vision amplifies ambient light into green images seen on a display screen in much the way cats see in the dark what we can't. The technology can be useful on night surveillance missions. But it's not suited for every task after dark.

Night vision requires some form of light. And because it works by amplifying light, if an intensely bright light is caught on camera, it overamplifies it to such a degree that nothing else appears in the screen. It's like a photograph developed from overexposed film. All you can see is the bright light obscuring everything else in the image.

Color is another differentiating factor. Night vision shows one shade of green. Thermal imaging shows images in black and white. A range of varying shades of gray distinguish how hot something is, with pure white usually representing the hottest temperatures. New technology allows users to switch the polarity on thermal imaging cameras so that the hottest spots appear as black, reversing the image like a film negative.

You Aren't a Firefighter

Although firefighters and police officers share the common goal of protecting people, most of the two professions' functions are quite different. So are their uses of thermal imaging.

This isn't to say that you can't use a camera designed for firefighters. But you should realize that they meet the specifications of another line of work, so they might not suit yours.

Law enforcement officers most often use thermal imaging cameras to detect subtle differences in heat, not the high temperatures of fires. Because of this, you should make sure that the camera you're using will detect the range of temperatures you'll be searching for. You'll want the camera to be resistant to environmental changes, but a burning building is probably not something you'll need to deal with.

Beyond temperature, what your camera will see, or its field of view, is an important consideration. Police officers often want the widest field of view possible so they can search a wide area at once. If your camera has a small field of view used by firefighters it might not suit your purposes.

Putting it to Use

Uses for thermal imaging cameras vary. But the 12 applications approved by the Law Enforcement Thermographers' Association (LETA) are the ones proven to stand up in court and meet other criteria that make them the uses of choice for police agencies.

If you aren't familiar with the organization, LETA is a group of volunteer active law enforcement officers who maintain a comprehensive Website designed to help agencies and individual officers better use thermal imaging on the job. The staff are a great resource for everything relating to thermal imaging as used by law enforcement. The biggest service LETA has done the law enforcement community, however, is developing its list of approved LE uses for thermal imaging.

These include search and rescue, fugitive searches, vehicle pursuits, ground surveillance, perimeter surveillance, officer safety, and structure profiles. (See box on page 45 for complete list.)

There are always new and creative ways to use heat-sensing technology, however. Traffic investigators have begun using thermal imaging to detect heat signatures from invisible skid marks to more accurately determine what happened when cars collided in road accidents.

One agency even determined that a drunk driver had been lying with the technology. The person was found next to his car on the side of the road and told responding officers a friend of his had been driving the car and then ran into the woods after crashing it.

Investigators determined the man had been the one driving by checking the passenger seat for heat. When they found it completely cold, they realized there never had been anyone there or he would have left a heat signature. The cops were able to end the investigation without wasting valuable department resources searching for a man who never existed.

Is it Worth It?

Many agencies have gotten beaten up in the press because they used homeland security grants to purchase thermal imaging equipment. While the equipment may be expensive to purchase, it's made to last a lifetime. And it can do what no other technology can. What it can do often ends up saving time and money by answering questions that otherwise would have taken lengthy investigations to answer.

If you think your department would benefit from using a thermal imaging camera, it couldn't hurt to check out funding options, such as grants. The LETA Website is an excellent resource for this information. Sharing one with local agencies could also help with funding issues. It might not seem like a necessity now, but the one time you need thermal imaging capability and don't have it could cost time, money, and lives.

Thermal Imaging Applications
Search and Rescue
Fugitive Searches
Vehicle Pursuits
Flight Safety
Structure Profiles
Ground and Marine Surveillance
Officer Safety
Environmental Law Enforcement
Hidden Compartments in Vehicles
Disturbed Surface Scenario
Traffic Accidents
Perimeter Surveillance