Going thermal

The increasing emphasis on homeland security — especially as it relates to ports and other large sections of critical infrastructure — has resulted in the development of technological tools that have enabled end-users to address security-related problems that were seemingly beyond their reach a decade ago. Examples of these technological advances are recognizable in any current security system design and include video analytics, IP-addressable security devices and Power over Ethernet enabled by IEEE Standard 802.3af.

However, thermal imaging cameras stand out as a particular class of technology that enables a new and effective approach to classic intrusion detection heat signature. Those of us familiar with traditional CCTV cameras that operate in the visible light spectrum expect the thermal imaging cameras (often referred to as infrared or IR cameras) to simply be an extension of the infrared sensitivity in modern digital cameras. At first glance, both cameras receive electromagnetic radiation from a source, detect and process it with a microelectronic chip, and pass the constructed video image to any of the current CCTV viewing and storage devices. However, the changes from the expected model are anything but subtle.

The essential characteristic of thermal imaging devices is that they operate by detecting the heat emitted by an object. This object could be a human body or a car whose engine is or has been running. The emitted heat signature by an object can be attenuated but normally not completely eliminated by fog, smoke, rain or other obscurants. This enables these devices to see the thermal image even when the visible light image is completely obscured. Examples of this are illustrated in the photos below where the visible and thermal images are compared side-by-side.

Light Spectrum

The chart on Page 32 illustrates the electromagnetic spectrum, ranging from the far infrared to the far ultraviolet. The world in which you and I as security practitioners tend to operate in is the visible light spectrum — with wavelengths ranging from approximately .4 to .7 micrometers (microns). Thermal imaging cameras work in the infrared range with wavelengths ranging from approximately 1 micrometer to more than 13.5 microns. Depending on the specific thermal imaging technology used, the infrared spectrum is further subdivided into medium wavelength, ranging from 3 to 5 microns, and long wavelength, ranging from 8 to approximately 15 microns. Most thermal imaging cameras used in security applications operate in the long wavelength portion of the spectrum. Thermal imaging devices used in military and in some long-range border detection applications operate in the medium wavelength range.

Lenses

Lenses on thermal imaging cameras are also different. Typical lenses for cameras operating in the visible light range of the spectrum are made of either glass or some plastics. However, glass is essentially opaque to infrared wavelength radiation; and many formulations of plastic used in CCTV lenses also offer poor thermal transmissivity in the infrared wavelength range. Therefore, lenses on thermal imaging cameras are usually made either of germanium or zinc selenide, which, interestingly enough, are opaque to visible light but highly transmissive in the infrared spectrum.

Detector

The CCD and CMOS sensors typically used in visible light cameras are sensitive to what is referred to as the near infrared (NIR .8 to 2.5 micrometers) portion of the infrared spectrum. This explains the nighttime performance of many current technology cameras in low light (not no light) at night with the IR cut filter removed.

Thermal imaging cameras operate in a different portion of the spectrum using different detection technologies. Thermal imaging cameras operating in the long wavelength range use a chip called a microbolometer. Infrared radiation strikes the detector material in the microbolometer, causing its temperature to rise, thus changing its electrical resistance. This change in electrical resistance can be correlated to the temperature of the object initially emitting the radiation and is therefore used to create a visual image. Microbolometers do not require cooling.

Thermal imaging cameras operating in the medium mid-wavelength spectrum employ a different technology that does require the chip to be cooled to increase the signal-to-noise ratio.

Purpose and Resolution

Thermal imaging cameras are primarily used in applications where detection, not identification, of an intruder is the goal. This is illustrated in the photos below, where the thermal pattern clearly represents a human; however, the lack of facial or body structure in the image precludes any further analysis leading to identification of a specific individual. While resolutions of 4 CIF and higher are available, most cameras deployed today for security applications have typical resolutions in the CIF range.

Coupled with the fact that the image is in black-and-white, the resulting digital image file is much smaller than security practitioners are accustomed to handling. As a result, the bandwidth requirements for a thermal imaging camera are miniscule by current security standards.

Other Features and Technological Developments

Current thermal imaging product offerings by FLIR and others offer many features that the industry has demanded of visible light cameras. Power over Ethernet (PoE)-enabled, IP-addressable devices are appearing on many of the newer models, allowing ease of integration of similarly equipped visible light systems.

Thermal imaging systems are also excellent platforms for video analytics. With visible light cameras, video analytic applications have to deal with a broad range of slight color variations — both in the background and the object to be detected. With a thermal image, the object of interest normally displays a high level of contrast to the background based on the temperature differential, making it relatively straightforward for video analytic detection.

Perhaps the most significant development is the price points on some of the newer models that might be appropriate for short-range facility and campus applications. Uncooled thermal imaging cameras are now available with a manufacturer’s suggested retail price of $3,000. While somewhat more expensive than a suitable visible light camera, these devices provide an ability to covertly monitor for movement without the expense and environmental considerations associated with providing lighting for a visible light system.

Expanding Markets

Borders and ports have represented surveillance and detection applications that were out of reach prior to the availability of thermal imaging CCTV systems. Given the limitations of human detection and the expense associated with providing lighting for a large-scale visible light camera system, securing large perimeters was essentially unaffordable. These devices provide the ability to view large fields of view at ranges that would make it nearly impossible for the human eye to detect even large-scale movement.

Some of the cooled medium wavelength devices are often coupled with a ground-based radar system. The radar system detects movement; the thermal imaging camera then focuses on that location to provide the security monitoring personnel a visible (thermal) picture of the detected object. These devices, often priced well above $50,000, address the previously unaddressable problems efficiently, and considering the alternatives, cost-effectively.

However, the bulk of the CCTV cameras implemented address the security concerns of more modestly sized facilities, campuses, high-end residential estates and infrastructure sites where the challenge is not one of physical scale but of cost-effectively providing a video record of site activities. As the price of thermal imaging systems continue to decline, and video detection — not identification — is an acceptable intermediate outcome, these systems will see expanded use where visible lighting is either not an option technically or is excluded prior as a consideration.

Making a Choice

With the number of thermal imaging system options expanding, it is important to know the salient technical characteristics and features to consider in order to select a product that will meet the requirements of a specific application. Drew Stone, international sales manager for ICx Technologies, says that the detector or pixel size is directly related to image quality — similar to the number of pixels in a digital image from a visible light camera. The smaller the detector size — normally measured in microns — the higher the pixel count and therefore resolution.

Chris Corsbie, director of marketing and communions for DRS Technologies, emphasizes the need for rugged and highly reliable systems, often arising out initial product development for military applications.

Dave Lee, marketing communications editor for FLIR, adds that the specifics of the project, including the environment, topography, target types and range requirements must be carefully considered when evaluating the suitability of a specific thermal imaging camera. Lee also included the availability of technical support and factory-trained technicians as important factor in selecting a particular manufacturer.

While not providing the high-resolution color images that we have come to rely on for the majority of our CCTV applications, thermal imaging CCTV provides the ability to obtain video images in no-light situations that are well-suited for video analytic applications. As their prices continue to decline, thermal imaging cameras will clearly find wider application.

Randall R. Nason, PE, CPP, is a corporate vice president and manager of the Security Consulting Group at C.H. Guernsey & Co. His experience spans a broad spectrum of the security profession including risk assessment and strategic security master plan development through complete system design, construction management, and design-led build projects. He has also recently designed and conducted full scale emergency response exercises for a federal agency. He is currently developing electronic security system related technical manuals, specifications, and training courses for the U.S. Army.

 

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