Nighttime intruders and criminals often have the luxury of unimpeded movement and access to valued assets in low-light environments. However, advances in camera technology improve visual capability at night, providing law enforcement personnel an advantage in surveillance operations.
Cameras used in nighttime surveillance are part of closed-circuit television (CCTV) systems that can be combined with automated video surveillance (AVS) technology. AVS automatically alerts security system operators and monitors of discrete, programmable events and are an integral component in today s surveillance applications and security operations. Selecting the right camera for a specific application is a critical factor in the overall performance of AVS capable systems in low-light settings.
We conducted an evaluation of AVS systems through the Department of Homeland Security s System Assessment & Validation for Emergency Responders (SAVER) program. Our goal: to measure their performance when integrated with enhanced cameras.
Monochrome vs. Thermal Imaging Cameras
Monochrome cameras are widely used in the security industry for low-light and nighttime video surveillance. Monochrome cameras are sensitive to the intensity of light energy with wavelengths outside the range of human visual perception, referred to as near infrared. These cameras record the various intensities of light to provide a brighter image in dark environments. The technology uses a charged sensor that detects available light and provides the signal to a digital signal processor to enhance the detected light in low-light conditions with back-light compensation.
High-performance monochrome cameras also reduce the noise in low light, offer excellent dynamic range, are responsive to the near infrared spectrum and have anti-blooming characteristics. In addition, when coupled with infrared illumination devices such as lasers, incandescent or light-emitting diodes produce an even brighter camera image. For this reason, infrared illuminators are often used for covert surveillance operations.
Thermal-imaging cameras provide effective long-range detection and have several advantages over typical cameras. Example: Unlike monochrome cameras, thermal imagers sense thermal energy instead of light energy. So, even in complete darkness, rain, smoke, dust or light fog, a thermal camera can produce an image from the various heat sources.
The thermal detector is the primary component of the thermal imaging camera. It s composed of various materials depending on the specific wavelength of infrared energy the detector is optimized for.
All objects radiate infrared energy in some way, and the camera can detect differences to 1/10 of a degree F. Thermal imagers offer a resolution of up to 320×240 pixels, which provides clear scene detail and long-range detection. Instead of using light to produce images, these cameras detect and use heat, so surveillance systems using these cameras don t require lighting. In addition, thermal-imaging cameras consistently perform in adverse weather conditions such as rain, snow and fog, and are widely used in waterway, lake and port applications.
Both high-performance monochrome and thermal-imaging technologies improve video images supplied to AVS systems, providing surveillance capability for both day and night environments.
Evaluating Surveillance Systems
AVS systems with either monochrome or thermal cameras are evaluated on their ability to detect intrusion in low light settings. Our intrusion-detection scenarios introduced a person wearing dark clothing entering an open field at different distances, velocities and directions. To evaluate all environments, we performed the scenario in wet, overcast conditions and dry, clear conditions. In addition, more advanced capabilities known as behavioral analysis were evaluated to measure performance differences for specific objects introduced into the scene, such as a person, dog or car.
On average, the thermal camera provided images detection at greater ranges than the monochrome camera. The thermal camera also provided the best contrast and distinguished a person from the environmental surroundings, regardless of the weather conditions, with only natural lighting. Over the sequence of the evaluation, however, the intruder s clothing became saturated from the wet grass and brush and displayed less contrast in the thermal image than during dry conditions.
The thermal camera was also more effective for long-range detection and in open areas. With infrared illumination introduced into the scene, the monochrome camera provided a dramatic improvement in the detection range for the AVS system and was comparable to the thermal camera, especially in wet conditions.
The thermal camera performed better than the monochrome camera during the behavioral analysis, primarily due to the contrast within the thermal image. The contrast allowed the AVS system to differentiate between the two living objects (a person and a dog) and their associated aspect ratio (the width of an image compared to its height).
However, several systems had difficulty differentiating between a person and a vehicle using the thermal camera. The thermal shape of the vehicle (the heated engine) was smaller than the actual shape of the vehicle, altering the aspect ratio of the vehicle, which makes classification less reliable.
AVS systems performed slightly better with the monochrome camera than the thermal in differentiating between the human and vehicle, but showed signs of blooming with the vehicle s headlights. This burst of light changed the image of the vehicle in the video, which makes classification difficult.
Conclusion
Currently, there are no industry standards for objective comparison of AVS systems and their performance. As illustrated by our findings, a system s ability to generate an alarm depends on the quality of video received from the cameras selected for the application. For this evaluation, the thermal camera provided images that enabled greater detection ranges than the monochrome camera. In more predefined or closer areas, the monochrome camera with infrared illumination proved more effective.
Bottom line: Choose cameras that best fit your situation.
The views expressed herein are the authors and don t necessarily represent the views of the U.S. Department of Defense or the Navy. The appearance of an external hyperlink does not constitute an endorsement by the DoD of the Web sites or of any products or services referenced therein.
Mike Besco and Dan Heater work for the Space and Naval Warfare Systems Center (SPAWAR) in Charleston, S.C.
To obtain a copy of our AVS night assessment: https://saver.fema.gov.
