Home System Design Thermal Imaging: The Tail Wagging the Dog?

Thermal Imaging: The Tail Wagging the Dog?

by Benchmark

Thermal imaging is enjoying a raised profile in the electronic security sector, and a number of manufacturers are now offering such devices. Benchmark wanted to look at the performance of some of the leading units, but before carrying out a full product analysis decided to investigate the potential on offer in security applications!

Thermal imaging has certainly arrived in the electronic security industry, and a mixture of dedicated imagers and hybrid units are available from a number of manufacturers. In the past few years, the technology has been increasingly promoted, and that – along with economies of scale driven by other industrial sectors – has put the topic of thermal-based surveillance firmly on the agenda. It is true that the technology carries a price premium, despite falling costs, and it is also true that the security industry didn’t go looking for thermal imaging. Indeed, the technology came to the security systems sector, and despite its track record in other theatres of operation, it is still establishing itself as a security-relevant option.

The real question is does the security industry need thermal imaging, or are manufacturers trying to force it into our thinking? Is this a case of a need being fulfilled, or is the tail wagging the dog?

It would be wrong to intimate that thermal imaging is a solution looking for a problem. Whilst the move towards emerging technologies has thrown up a few of those, thermal imaging clearly has benefits for the electronic security sector. However, history shows that benefits alone sometimes aren’t enough to see a technology adopted.

Thermal imaging has two main problems, according to integrators and end users that Benchmark has consulted. The first is that the sales story for thermography in security isn’t always compelling. The second is that the price premium does make some consider other options that are available, often with the ability to deliver a similar result at a lower cost.

Taking the first issue, the sales pitch for thermal imaging tends to take one of two routes, neither of which present the technology in the best way. Many tend to take the option of comparing thermal imagers to cameras, and highlight the fact that the units operate in total darkness, fog, smoke, etc.. Of course, whilst the devices can be used as an alternative to video cameras, the end results are very different, and such comparisons can actually understate the benefits of the thermal option.

Video is an optical technology, and uses light to create visual representations of a scene. The resulting images have high levels of detail, and replicate what we see with the human eye. Of course, if light levels are low, or if there is some type of environmental obscuration, the images will often be unusable. With video, if you can’t see it, there is nothing of value to capture or view!

Thermal imaging is not reliant upon light, because its image is not an optical one. Instead, the imagers use thermography, detecting the emission of radiation from objects. All objects over absolute zero emit electromagnetic radiation at differing levels, dependent upon their temperature. This radiation is what forms the thermal image.

The difference between the two technologies is significant, and any consideration of optical imaging and thermography on a ‘like for like’ basis will typically not be helpful, and could leave the final customer with a system that does not deliver what they expect.

The second approach often likens thermal imaging to long range detection. While thermal imagers can be used to detect, to pigeon-hole the technology in such a basic way is arguably less helpful than comparing it with video!

If you consider the perceived value of thermal imaging, the costs may seem high if the technology is compared to other product types that carry a lower price and have a proven track record in the field.

The reality is that thermal imaging does offer a wide range of benefits, and is also cost-effective. It’s not a low cost technology, but if employed correctly, and if understood by the integrator and the end user, it can represent value for money.

By understanding what thermal imaging can do – and what it cannot do – it is simpler to ascertain whether or not it fits into any given application. Because of the mixed messages in the market, Benchmark decided to assess the overall technology prior to testing the individual products.

Benefits viewed

To really dig into the benefits of thermal imaging, it is important to stop thinking about visual information, and to start thinking about heat. For example, a living being will typically generate more heat than an ambient location. A vehicle that has recently been driven will generate more heat than one which has been parked for some period of time. Even events which have occurred previously can leave a thermal imprint. For example, a heavy item being dragged creates friction, which in turn generates heat.

Thermal imagers aimed at the security market have less adjustability than higher spec units for other uses, and as they are uncooled they usually work best when there is a significant differential in temperatures. This makes them simple to deploy, but does rule out some of the more intelligent uses that other industries take advantage of.

However, when you start to consider large or open sites, protecting the perimeter with thermal imagers as a part of an overall solution does make sense.

For example, if an intruder conceals themselves in bushes or undergrowth, traditional video surveillance cannot detect them. Also, if an external detection system generates an alarm, the system operator can often be at a loss as to what has caused it. Even where video surveillance is linked to the detection device, environmental conditions might make it difficult to ascertain the cause.

Benchmark ran a series of basic assessments using the thermal imagers to be tested in the next issue. What was interesting was that when the technology was discussed with a few end users we were using for general feedback, they were initially very excited by it. Then, on viewing the test images, their enthusiasm quickly waned. If anything, they were disappointed with the results.

However, once the technology was used to tackle situations that other security devices simply could not address – concealed intruders, verification of alarm triggers during hours of darkness, target tracking, etc. – their enthusiasm quickly returned.

The reality is that the outputted images from a thermal imager are not high quality, and cannot be used for identification. At a time when end users are used to high definition video and megapixel cameras, a VGA resolution thermal image lacking visual detail can be a tad underwhelming. However, when the technology is applied in applications where heat differentials can deliver information that video simply cannot, the benefits are obvious.

Whilst thermal imaging does not deliver sufficient detail to positively identify individuals, it does give some details that might not be expected. Our general assessment showed that many vehicles with sign-writing can be identified. This is because vinyl lettering has different thermal properties to those of the vehicle body. Many materials have differing levels of emissivity, and this difference can be seen in a thermal image. Indeed, the more you understand emissivity, the more you can appreciate the various applications for thermal imaging devices!

Because the image quality cannot be used for identification purposes, thermal imagers can deliver longer ranges than traditional cameras. Thermal technology delivers the ability to verify that an event has occurred (or is occurring), rather than identifying the culprit. However, care should be taken to consider operational ranges, which can be an issue given the way that thermal performance is quoted – more about that in a moment. However, it is worth considering the larger areas that can be covered by these devices, because it does somewhat justify the price premium.

Caution advised

There are a number of elements relating to thermal imaging that must be treated with caution. One of the more important issues is that often you will see figures quoted for range. These include claims for ‘detection’ and ‘identification’, and can cover kilometres rather than metres!

It is very important to realise that these figures are based upon the Johnson Criteria, which was designed for military needs. Their definitions of detection and identification are very different to those of the security market!

For example, if you are involved in a military action in – for example – a desert at night, you will want to know if anyone is approaching. In the Johnson Criteria, the requirement for detection is just two pixels. All you need to know is that something, whatever it might be, is within a certain distance, so you can direct an ordnance strike. However, in a security application, you don’t want to be generating an alarm event for a fox or rabbit!

Whilst manufacturers might claim detection at two kilometres, for security purposes our assessments show that a target would need to be no more than 200 metres away if you were to be able to positively identify it as a human. If the target was crawling or moving in a unusual way, such as if the intruder was crouching or squatting, the distance would need to be further reduced.

Often, manufacturers will show thermal cameras still operating with the camera covered with a plastic refuse sack. Again, caution needs to be exercised. This can be achieved with relatively lightweight plastics, but most materials will actually obscure the view. It’s a demonstration gimmick, and the end user shouldn’t be given the impression that the unit will defeat attempts at blocking the lens.

It is also worth remembering that thermal imagers cannot see through glazing.

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