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Out of the darkness.

Out of the Darkness

WHEN A SECURITY PROFESSIONAL spends several nights in a warehouse parking lot hoping to identify suspected drug dealers, he or she is coming face-to-face with the one factor that has frustrated the security and law enforcement communities for centuries: the cover of darkness that shields nighttime crime.

Now, thanks to technological advances in infrared (IR) camera technology, that cover is being shattered.

IR cameras are ideal for night surveillance because they require no light source whatsoever. While for years some form of IR imaging has been available for surveillance applications, today's IR systems represent a significant technological leap. The shadowy images traditionally associated with IR cameras are giving way to video pictures clear enough to detect individuals from a mile away.

Today's newest IR cameras offer a dramatic improvement over existing IR systems because they feature focal plane array technology. Once the exclusive domain of sophisticated aerospace and military imaging systems, high-quality IR focal plane arrays have been refined to give security professionals affordable see-in-the-dark technology. Designed to integrate into existing CCTV systems or operate alone, these new, high-resolution cameras are rugged, easy to operate, and portable. IR CAMERAS CAN BE PUT TO WORK wherever poor visibility hampers the performance of visible CCTV cameras. With IR cameras in place, as much as 50 percent of a facility's night lighting costs can be eliminated for both interior and exterior surveillance.

Inside buildings, IR cameras can replace visible CCTV cameras in areas where lights are burning solely for the benefit of the cameras. In fact, IR cameras operate best when there is little or no ambient light.

IR imaging should also be considered for any exterior environment where it would be more cost-effective to install a single camera than a bank of lights for night surveillance. Parking lots, facility grounds, and loading docks are ideal candidates for IR.

IR imaging can also be effective for surveillance in remote locations. Since it doesn't rely on light sources, an IR camera can record events wherever and whenever suspicious activity is suspected, from the darkest, most secluded corner of a parking structure to a fog-bound oil derrick.

The new battery-powered, focal plane array cameras can also be installed in surveillance vehicles for around-the-clock recording. Like visible video cameras, IR cameras used on vehicles should be mounted on a gimballed, vibration-isolation tracking system.

Since they detect minute temperature differences, IR focal plane array cameras can record automobiles and other inanimate objects as easily as they image humans. An IR camera can also help determine if a vehicle has been operated recently. Since most vehicles maintain a particularly intense thermal signature for about an hour after the engine is shut off, their IR picture shows vivid temperature intensities.

In fact, IR cameras can even detect whether a vehicle has been moved from an area by sensing the thermal energy left by the vehicle at its previous location. IR images can also help ascertain whether guns or explosives have been fired or detonated recently.

While moonless nights and dark hallways may immediately come to mind as the prime settings for IR imaging, don't forget the surveillance challenges posed by inclement weather. The performance of visible cameras can be extremely limited during rain, fog, and snow. However, since people and objects generate and emit heat regardless of the weather conditions, IR cameras provide excellent pictures even in the most severe conditions.

ALL IR CAMERAS WORK BY CONVERTING heat radiation from people and objects into video images. That is why they operate independently of illumination.

For years, security and law enforcement professionals have had access to scanning IR systems and pyroelectric vidicon. Both technologies are adequate for detecting the presence of objects and people, as long as picture resolution isn't a critical factor. However, at any appreciable distance, the image on the screen appears to be nothing more than a white blob.

The scanned cameras employ one to eight IR detectors. They scan a scene with rotating or oscillating mirrors to pick up heat radiation, then electronically establish the differences between the temperatures. The scene temperature is eventually rendered as a standard RS-170 image display--compatible with the display required for visible CCTV cameras.

While scanned IR camera systems are considered an established technology, they lack sensitivity and dynamic range and their image quality cannot match that generated from an advanced focal plane array.

Pyroelectric vidicon IR cameras detect temperature changes rather than IR photons. While these cameras may be attractive because they do not require advanced cooling systems, they provide very low resolution.

In contrast, images from the new focal plane array cameras feature very high resolution because their pictures represent temperature differences as well as the temperature intensities of the subjects being monitored. The cameras do so with a "staring" focal plane array.

In a staring system, thousands of IR detectors (in the case of one commercial camera, more than 65,000 detectors) acquire image data for an entire scene simultaneously. The detectors stay on the scene long enough to capture sufficient image data to produce sensitive, high-contrast images.

The advantage of focal plane array cameras is most obvious when one examines highly detailed images, such as those of a person's face. State-of-the-art cameras incorporate detectors made from an exotic semiconductor material called indium antimonide (InSb). To date, InSb cameras offer the greatest sensitivity available in any commercially available IR camera system. RESOLUTION FOR IR IMAGERS IS MEAsured by detector organization. Highly sensitive InSb focal plane array cameras with resolutions as high as 256 5 256 are currently on the market. These numbers mean the focal plane array consists of 65,536 detectors arranged in a 256 5 256 matrix.

Another specification that differs from visible cameras is shutter speed. In the IR world, this spec is known as frame speed. The best IR focal plane array cameras can provide adjustable frame rates up to 1,000 frames per second. When used at 30 frames per second, the speed is comparable to VHS cameras and television. This frame rate is sufficient for capturing extremely highspeed activity, such as fast-moving vehicles.

Several other factors influence one's choice of camera besides allowable distance, resolution, and shutter speed. They are as follows:

Color. IR cameras assign colors differently than the human brain does. With IR cameras, colors may be arbitrarily assigned to specific temperature ranges. IR images don't provide a photographic reproduction of a scene; instead, they represent the differences in thermal intensity of individual pixels. Color values are assigned to as many as 256 levels of pixel intensity.

Some scenes, such as an animal running along a snow bank, may yield a sharp contrast in intensity between the subject and the background. Scenes with such extreme temperature differences can be presented adequately by a black-and-white IR camera.

Where the pixel intensities are more subtle, however, such as in shots of people walking through a crowded manufacturing plant, the eye may interpret the differences better if the thermal intensity variations are mapped in color.

An IR image of a man's face might show orange skin and blue hair, as well as various shades in between. A black-and-white image of the same person would be less distinct because the eye can interpret fewer intensity levels than it did in the color image.

Optics. A wide variety of telephoto and zoom lenses is available for IR cameras. A camera's focal length can be lengthened or shortened depending on specific requirements. A long-focal-length telescopic lens extends the camera's capabilities, allowing it to acquire images from as much as a mile away.

The type of lens chosen depends on the particular application. IR optics are more costly than the quartz optics used by visible cameras because IR lenses must be fabricated from expensive silicon and germanium materials.

Integration. IR cameras are designed to be unobtrusive and can be installed wherever a visible camera is placed. Today's new IR cameras are easy to integrate into existing CCTV systems. They generate an NTSC (National Television Standards Committee) signal and are compatible with standard monitors and VHS time-lapse video recorders.

These cameras can be interfaced with switchers and alarm systems and remotely controlled from a PC, right along with the visible cameras in the system. No special cables are required. Any experienced security system installer can integrate an IR camera into a CCTV system.

The only extra step involved in setting up an IR camera is a calibration process to ensure that the pixels respond uniformly. Some of the new cameras automatically calibrate themselves with the touch of a button. With others, the user is required to point the camera at a hot source, followed by a cold source. The camera then automatically calibrates. As with visible cameras, the display, gain, and contrast of an IR system must be adjusted before it is put into operation.

Maintenance of IR focal plane cameras is a simple matter. A check on pixel uniformity should be performed once or twice each day. This is accomplished in much the same way as the initial calibration--with just a touch of a button on the camera, followed by pointing the camera at a cold source.

Cost. Focal plane array IR cameras start at about $30,000. While this is a steep jump from the cost of older-technology IR systems, the return on investment for the newer cameras can be substantial. Focal plane array systems can see far more in zero-visibility conditions than other types of cameras. And the quality of imagery far surpasses the best pictures from scanning or pyro-electric IR cameras.

Focal plane array IR cameras can drastically reduce utility costs because they eliminate the need for excess lighting. In many situations where continuous surveillance is needed, these cameras can replace visible cameras and their attendant illumination requirements. CCTV systems that cover stadiums, parking lots, and other massive areas reap the biggest cost savings.

High-quality IR imaging lets security personnel expand the scope of their surveillance activities because its performance is not restricted by lighting or weather. The power of IR imaging to catch illegal activity that would otherwise go undetected can drastically reduce the threat of crime.

And finally, the cost of IR focal plane array cameras looks small when one considers their advanced technology. Comparable systems used by the military and scientific communities have cost upwards of $75,000.

IR technology has advanced enough in the last 10 years that security professionals can feel confident they are investing in a mature technology. Future IR cameras will offer improved resolution and range, but systems purchased today will continue to serve the most demanding security requirements for years to come.

As more surveillance systems enjoy the benefits of IR focal plane array technology, the IR camera is likely to become a standard piece of equipment in CCTV systems. And industrial crime will, once and for all, come out of the darkness.

PHOTO : Pictures from the new focal plane array cameras use color to represent temperature differences and intensities.

Jeff Frank is vice president of electronic systems at Amber Engineering, a manufacturer of infrared cameras in Goleta, CA.
COPYRIGHT 1991 American Society for Industrial Security
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:night surveillance using infrared cameras
Author:Frank, Jeff
Publication:Security Management
Date:Aug 1, 1991
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