An old chinese proverb says that it’s better to light a candle than to curse the darkness. Many companies stumped by the challenges of achieving surveillance in the darkness may be tempted to curse their predicament, but there are several tools—far better than candles—that they can use to attain the night vision they seek.
There are imagers that detect temperature changes and lasers and light beams that can be shot out to illuminate large areas. There are also camera sensors that can produce images by using a type of atmospheric energy not visible to the human eye. Here’s a look at some of these technologies, their strengths and weaknesses, and a few examples of applications where they are proving effective.
Thermal imaging technology allows cameras to capture anything that gives off heat. They use the infrared spectrum and, therefore, require no light. Thermal cameras are essentially monitoring temperature changes in the field of view, according to Christiaan Maras, Eurasia marketing manager for Portland, Oregon-headquartered FLIR Systems, Inc.
Since the human body gives off heat, thermal imagers are effective at deciphering whether there are trespassers in an area. And more sensitive thermal imagers let users know the difference between a person and an animal.
There are both cooled and uncooled thermal detection options. According to FLIR, cooled thermal imaging cameras are integrated with a cryocooler that lowers sensor temperature, which allows the camera to reduce the thermally induced noise in a picture, making for clearer images. Cooled systems are more sensitive to temperature differences than uncooled, and tend to be used in longer ranges, but they are much more expensive, and their cryocoolers need rebuilding after about 10,000 hours of operation.
Uncooled thermal cameras do not use cryogenic cooling. These systems tend to be appropriate for applications in which users do not need to detect something past about three miles, explains Maras. Uncooled thermal imaging systems also need less maintenance than infrared-camera systems with illuminators because they don’t have bulbs that may need to be replaced.
A thermal imaging system, whether cooled or not, provides only outlines of the heat contrast on an individual or object, rather than the detailed picture CCTV cameras normally provide. “It can just say, ‘I think that’s a person running around doing something bad,’” says Product Marketing Manager Willem Ryan of British Columbia, Canada-based Extreme CCTV. He calls thermal imaging a “seek and detect” technology.
Integrator Roberto Pablo, applications engineer for RFI Communications and Security Systems, says that thermal imaging cameras are, therefore, generally recommended for long-range needs where intrusion detection, not identification, is the goal. He cites border patrol as an example: “I don’t need to identify [people crossing the border] but I just need to know there’s somebody out there crawling, there’s a heat signature, and if I can identify that between human and animals, then…my officers can be alerted and say, ‘Hey…there’s somebody out there trying to cross the border.’”
For the same reason, thermal imagers are effective in fog and types of inclement weather where other camera options might have problems getting an adequate image or making any sort of detection. Thermal cameras also can be a good supplement in broad daylight because, unlike normal cameras, they can detect a person trying to hide in shadows, bushes, or a forest.
Maras points out that thermal imaging cameras are “passive” systems, because they are not beaming any types of lights or lasers out at the field of view.
FLIR has provided thermal imaging cameras at the London Eye, a cantilevered observation wheel that provides visitors a view of London’s landmarks and receives an average of three million visitors a year; at France’s Port of Calais, where the cameras detect people trying to illegally cross the English Channel; at Copenhagen Airport, where the cameras search for unauthorized persons in a secure area; and numerous other locations.
Maras says the prices on thermal imaging cameras have come down quite a bit over the past few years due to increased demand. FLIR’s most economic option is around $4,000, says Maras.