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Visualising without seeing

Matthew Guo discusses the benefit of thermal cameras.

Matthew Guo, Hikvision SA.

One of the most exciting technologies in the security arsenal is thermal imaging, which essentially gives cameras the ability to monitor through darkness, fog, rain and other limited or zero visibility environments. The reason for this? These cameras do not ‘see’, they ‘visualise’ – translating infrared radiation into pictures.

Infrared (literally ‘below red’ in the colour spectrum) was discovered in 1800 by Sir William Herschel as a form of radiation beyond red light. The first thermal cameras were developed in 1929, when a Hungarian physicist invented the infrared-sensitive (night vision) electronic camera for anti-aircraft defence in Britain. Once their value was recognised and their prices began to drop over the past ten years the innovation ball started to roll. It’s now available for more applications and broader markets – from its original use in the military and for border protection. Applications for this technology are now varied – from allergy detection and veterinary medicine, to detecting leaks in industrial piping.

Applications

The technology can be used to detect fires, and more specifically to help fire-fighters to find the core of a fire. Where a visual camera would be blocked by the smoke, a thermal view can show where the fire is.

But the security industry has a wide-spread use of thermal technology. Thermal imaging provides benefits which daylight cameras can’t. Thermal imaging works without any illumination for detection, with no need for expensive light installations. Also, thermal imaging works with longer detection ranges than traditional CCTV, saving installation costs as fewer cameras and poles, etc are needed.

Thermal cameras can be used to great effect in perimeter security, for example. Even in the darkest areas that traditional cameras cannot see, a thermal camera can pick up movement and give security teams eyes on objects, vehicles and intruders, even if they are entirely dressed in black. It’s particularly useful for security solutions in markets such as critical infrastructure, airports and facilities. Combined with VCA technologies, like line crossing and intrusion detection alarms, these can really provide a comprehensive security solution.

The industry landscape for thermal technology is widening, with various thermal specialist plying their wares to solve all kinds of problems. In the security industry too, many of the main players work with thermal technology. Hikvision developed its first thermal camera back in 2008 and by 2010 this had developed into a thermal network camera. In 2015, Hikvision research and development created an independent camera module of its own.

There are three types of camera/detector:

1. Thermal imaging detectors and cameras designed to visualise the thermal radiation of objects in an area. Typically shown in a greyscale, this could be in SWIR, MWIR and LWIR waveband. LWIR is standard in the market (for cost reasons). Most common applications are security and surveillance (e.g. perimeter protection and area surveillance).

2. Thermal cameras designed for security applications, but with the possibility of use as radiometric cameras for thermography. These are typically used for condition- and temperature monitoring, fire

prevention and detection, or in industrial safety applications.

3. Detectors and cameras designed and calibrated for test and measurement. Via additional parameters (e.g. emissivity, reflective temperature, etc.), the cameras display absolute temperatures with accuracy of ± 2°C or 2% (depending on camera type), typically in coloured scale.

The technology

The principles of thermography are based on the fact that light radiates beyond the visible spectrum. Called infrared, this radiation is emitted by all objects with a temperature above absolute zero (-273°C), and is measured in nanometres (m). This itself is split into three ‘bandwidths’ – near-infrared, at 0.4-2.5 m; medium infrared, at 3.5–4 m; and thermal infrared, at 8-14 m. The term used for this is emissivity.

Since thermography measures the infrared radiation emitted by an object (or person), and each one at a different wavelength, it’s possible to make a picture of the environment without any visible light. The term ‘thermal’ comes from the fact that the amount of infrared radiation given off increases with temperature – therefore a cold surface will be seen differently to a warm-blooded person. There are also differences depending on the type of surface and materials. For example, human skin would have a different emissivity to steel. Emissivity also varies by factors like surface roughness and shape, viewing angle and the degree of oxidisation (of a metal).

It’s also important to note that, because the emissions are given off by the surface of an object, imaging cannot see through materials that the human eye would be able to. So, for example, although the human eyes (and regular cameras using visible light) can see through a window – a thermal device would only be able to see the emissions given off by the glass itself.

A thermal camera uses a specific type of lens – a Germanium lens – to reflect visible and ultraviolet light, only letting infrared through. Inside the camera, uncooled focal plane arrays change the infrared thermal radiation to an electronic signal, which is then used to form an image. Usually the image output is in a kind of ‘greyscale’ format, but in recent years the use of ‘pseudo-colour’ has been used to make the images easier for the human brain to process.

The science of infrared detecting has many applications, not least in the security industry. Combined with regular lenses and smart functions, like intrusion detection, this technology provides an invaluable addition to security solutions.

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