Feature article: Thermal technology – visualising without seeing

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 in fra-red radiation into pictures.

Introduction

Infra-red (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 TV camera for anti-aircraft defence in Britain. Once their value was recognised and the 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 firefighter to find the core of a fire. Where a visual camera would be blocked by the smoke, a thermal view can show where the hottest part of 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.

See below how thermal imaging can pick out a person where a traditional camera cannot, even quite close up.

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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 is LWIR (for cost reasons). Most common applications are Security & 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-, 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. Most common applications are electrical, building and industrial, but they can also be used in medical, science and R&D applications.

The technology

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

Since thermography measures the infra-red 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 infra-red 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 infra-red through. Inside the camera, Uncooled Focal Place Arrays change the infra-red 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.

From the images below, the differences can be seen clearly. The regular camera (on the left) can only see the lit area in the foreground, but there is not enough light for it to see the background. The thermal camera however, on the right, does not view the visible light, and therefore is not affected by the shadows it creates, or the dark environment. In that picture, a figure can clearly been seen on the hill in the background, a long way away.

Summary

The science of infra-red detecting has many applications, not least in the security industry. Where regular cameras cannot see – for instance in very low light, fog or other bad weather conditions or smoke-filled areas – thermal technology can provide a clear image. Combined with regular lenses and smart functions, like intrusion detection, this technology provides an invaluable addition to security solutions.

Hikvision is always pushing the boundaries of technology, innovating to meet ever-increasing needs of the security community.

The products lead the market in three ways. They create better images due to an independent research and development module on the cameras themselves. They include better smart functions giving smart analysis functionalities. Finally, they are suitable for better applications, including temperature exception and fire detection.