Product Details - Dedicated Microcomputers Limited

We live in a world where the growth of terrorism, violence and vandalism demands ever-increasing levels of security. Thermal Imaging (TI) is a technology which provides the ability to see whatever the prevailing lighting levels and in difficult weather conditions, and this unique ability to see in total darkness makes it an ideal tool forsecurity and surveillance applications.

Until recently this sophisticated technology was prohibitively expensive, being driven in the main by military applications; over the last few years however, the technology has improved and it has been introduced to high volume commercial and professional applications by innovative companies such as Irisys. This has brought the price level down and in turn opened up a host of new applications.

Appropriate thermal imagers no longer need to cost £80,000 or more and it is the affordability of the current generation of imagers that makes them eminently suitable for the mainstream security and surveillance marketplace.*

The Advent of Thermal Imaging
First used by the US Military during the Korean War as a classified surveillance tool it really began to develop during the 70’s when national governments (notably the US and France) began heavily investing in R&D of Thermal Imagers - to improve the quality and reduce the size - solely with the aim to gain an advantage on the battlefield. The resulting years of development produced the selection of Thermal Imaging equipment available today, and as development continued costs began to fall to the point where TI is now accessible for mainstream commercial applications.

Thermal Imaging: The Theory
Thermal imagers measure the infrared energy emitted or reflected by objects in the field of view. The amount of energy emitted depends on the temperature of the object. The IR detector contained in the TI converts IR energy into an electrical signal. This is converted by the TI into a visible temperature patternc called a Thermogram. As different surfaces (and different parts of the same surface) can emit different IR energy the TI can build up an image Where ‘hot’, ‘cold’ and various states in between can be displayed. In addition as the TI works outside the visible spectrum it does not require ‘visible’ light to operate allowing it to be used in complete darkness.

Why Use Thermal Imaging
As TI becomes popular in mainstream commercial applications many are asking ‘why’ they should use it. Whilst a TI will never provide the same detail as a conventional CCTV camera it carries some very clear benefits over and above its traditional security counterpart.

It does not rely on ‘visible’ light and can be used in any lighting conditions including complete darkness
Its sensitivity means that it can see beyond the range of traditional IR lighting which will only really have an effective range of 200m – ideal for long range surveillance Its long range effectiveness reduces the need for multiple cameras at measured intervals to ensure surveillance coverage It can be effectively combined with Video Content Analysis – people / vehicles have already been separated from the background, before the VCA processing of the picture has even begun. The removal of night-time lighting, helps reduce customers CO2 emissions Its ability to see through fog and mist allows it to be deployed effectively in maritime environments

The Components of a Thermal Imaging Camera
There are two main components to any TI; The Detector and The Lens, the various options available will determine not only the cost of the unit but also the main application it is used for.

Detector
There are two options for a thermal imaging detector, cooled and uncooled, both types of detector absorb infrared energy which in turn affect the detectors electrical properties to produce an image.

Cooled Detectors
Cooled detectors use narrow gap semiconductors to offer high sensitivity to infra-red radiation. These semiconductors have to be housed in a vacuum sealed case and cryogenically cooled (typically to below a temperature of 110K). This cooling is what enables the Cooled Detector to remain so sensitive to heat changes. Without the cooling process the
detector would be overcome by thermal noise from the semiconductor.

As a cooled detector has greater sensitivity, it can use high F-number lenses (a smaller aperture) and therefore can be combined with long range lenses. This combination of sensitivity and focal length has led the Cooled Detector to be the preferred option for long-range thermal imaging surveillance easily allowing identification of a human form at over 4Km.

However, although the lens may be cost effective, the technology required to operate a Cooled Detector (the cryogenic cooler) and the on-going cost of maintenance means that they are significantly more expensive to own than their cooled Counterpart. Cooled TI cameras can cost over £100,000 per unit and still remain largely the domain of military.

Uncooled Detectors
Despite the high sensitivity to IR radiation offered by Cooled Detectors, they can be too expensive (and impractical) for a security installation wishing to add TI to its system. As a result Uncooled systems have become popular. Typically operating at ambient or ‘room’ temperature Uncooled Detectors commonly use microbolometer technology (or pyroelectric/ferroelectric materials) to detect temperature changes and convert these via electrical signals to a TV image. A coating is applied to the microbolometer to absorb IR Radiation which heats up and causes a change in its electrical resistance, this in turn produces an electrical signal which is used to create an image. Common materials for
microbolometers include Vanadium Oxide (VOx) as used by FLIR, and Amorphous Silicon (α-Si) as used by Dedicated Micros.

Because they are Uncooled, and don’t require expensive cooling systems they are significantly cheaper than their cooled counterparts (they can now be purchased for £3500). However because they are uncooled they are less sensitive to IR radiation and are not ideal for very long range surveillance. These facts combined mean that an Uncooled TI is the clear choice for the majority of Security Installations requiring thermal surveillance.

The Thermal Imaging technology used by Dedicated Micros in its Infiniti Thermal uses an Uncooled Detector that uses an Amorphous Silicon (α-Si) microbolometer.

Lens
The Lens of a TI is not made out of glass like the lens of a normal CCTV camera. The properties of glass mean that it does not transmit infrared radiation very well and would be an impractical lens material for thermal imagers. Instead Germanium is used for TI lenses.

Germanium is a naturally occurring chemical element that is transparent to IR Radiation (that is that it will allow IR Radiation to pass through it). Although abundant on the planet, few minerals contain it in large concentrations making Germanium expensive to mine. This, combined with its semi-conductor properties and uses in communication equipment such as fibre optics mean that Germanium carries a high market value (currently 1Kg of unprocessed Germanium is £800, the equivalent weight in silicon is £1).

The high price of Germanium makes it a significant factor in the cost of any TI system. Obviously the more germanium used on the lens, the higher the price of the system. This explains why thermal imagers that can see further that 2 kilometres (and therefore require large lenses) are significantly more expensive than those designed to focus on less than 300m.

Finally there is the factor of size. Long-range thermal imagers require large lenses. These large lenses are heavy and will require significant support for stability, especially if elevated on poles or platforms. All of which contributes to the cost of a system and explains why many integrated TI/CCTV Camera combinations (which often have compact housings) are designed for surveillance at ranges of under 2 kilometres.

Detection, Identification, Recognition
CCTV usually uses a specific set of guidelines for Detection, Identification & Recognition (DRI) of an item or person. This typical equates to D=10%, R=50%, I=120% of screen height.

Although thermal imaging uses the same set of criteria, it was originally developed for military applications, such as surveying a battlefield, and uses the criteria in a more subjective way.

• Detection: Recognition of a heat source approximately 3pixels high on-screen
• Recognition: Distance at which the object can be recognised – person, animal or vehicle etc.
• Identification: Originally used by the military for identification of friend or foe - typically half the Recognition range.

This difference can be misleading for security installers and integrators who are not used to TI technology and can be confused by the specifications provided to them by manufacturers. For example ‘Detection’ in the CCTV world equates to an object being 10% of screen height. The equivalent on a thermal imaging camera would be 0.5% of screen height. And this is the reason why Thermal Cameras are able to ‘Detect’ at such great distances compared to conventional CCTV cameras.

Conventionally, the DRI ranges are stated as being for 50% probablilty of detecting a fixed target. In practice, a moving target is more easily detected by an observer. The DRI range is usually best-case and takes no account of atmospheric attenuation which can be a factor a longer ranges especially in mist or fog.

For practical CCTV type applications a reliable level of detection in a wide range of conditions will be achieved at 60-70% of the theoretical D range.

Night-time surveillance & ‘Dark Skies’
Thermal imaging benefits the user with the ability to keep their site in entire darkness during the night. This not only saves on power and maintenance bills for IR Lighting and floodlights but also contributes to the ‘eco-agenda’ by reducing unecessary light pollution in both urban and rural areas (referred to as the ‘Dark skies Initiative’ in many countries around the world – see http://www.darksky.org for further details).

Typical Applications
As it requires no external lighting and can provide images of intruders even when obscured by fog or smoke, the thermal imager is ideal for use as a security tool in a wide range of establishments. The deployment of thermal imaging may be within a site, to monitor the perimeter area or to protect specific high value assets. Common examples of such applications are:
• Government premises, embassies, parliament buildings, law courts, correctional facilities
• Public facilities, stadiums, schools, hospitals
• Commercial complexes - retail outlets, utilities, warehouses, factories, hotels, R&D Centres, car parks, cash centres, data centres
• CNI (Critical National Infrastructure) - airports, train stations, nuclear power plants, petrochemical facilities, pipelines, bridges
• Military establishments – barracks, airfields, fuel and ammunition depots.

* Information courtesy of Irisys