#Pelco
D. Karneev.
Thermal imager. The choice of a professional (MiB No. 6/2007)
«Peace and Security» No. 6 for 2007
You can't hide your warmth!
If there is an intruder, then he is warm!
As security professionals, we have a lot of technology under our belts, from cameras to ID badges. We use various systems to control access to the businesses we protect, while keeping up with technological advances and new developments in our field. So, I’m writing this article to tell you that we have a new game: security thermal imaging cameras! Part One. There’s a New Player in Town
Unlike the human eye, thermal imagers do not use visible light to form an image, thermal imagers use heat. This gives them a particular advantage over low-level and daylight cameras when lighting is impractical, expensive, or long range is required. For years, thermal imagers have been very expensive and we have been approached with cheaper, less capable options — night vision and IR illuminators. Why? With high-quality thermal imagers available on the market for $5,000 to $10,000, we are selling ourselves short if we do not clearly understand this technology, and there will be few who will pay us to protect themselves.
Why do I care?
The simple answer to this question is… range. In this business, range is the equivalent of time: time to react, time to decide, time to respond. Security thermal imagers are constantly detecting the slightest changes in the heating of everything around us. This thermal energy is much easier to detect at greater distances than visible light, which gives thermal imagers a direct advantage. In Figure 1
The thermal imager clearly shows that someone is trying to break down a car door. A small boat is shown in Figure 2. The corresponding images from a camera with IR illumination and a night vision device show their capabilities from a distance of 150 m.
But the advantages of thermal imagers don't end there. Thermal imagers not only see further, but they are also immune to most countermeasures open to those who counter means based on visible or reflected light: camouflage. Why? The answer is simple: you can't hide your heat.
A camera with an IR illuminator was closer than 150m from a person dressed in dark clothes on a moonless night. The result is disappointing. The same thing happens with a night vision device — the result is zero. But a thermal imager easily detects an intruder.
Sure, you might say that with a camera with an IR illuminator you can better identify the offender than with a thermal imager. That's true, but think about it: if the offender is close enough that you can identify him, you might have to look for a new job, and the offender might already be eating in your cafeteria. Use a thermal imager and identify the offender when he is in handcuffs!
Thermal security cameras are very useful in cases where they force cameras with other technologies to fight for second place. Large enterprises usually have areas without fences and unlit areas due to economic and other reasons. Thermal imagers see far enough to make this a “no-brainer” and, what’s more, they do the job for less money than building the infrastructure for low-level cameras and cameras with IR illuminators.
How does it work?
It may seem incredible, but this is not nanotechnology or the space industry. Thermal imagers work on simple natural laws.
We see reflected light. Cameras with IR floodlights, night vision devices and the human eye all work on the same principle: light radiation hits something and is reflected back. A detector then receives the reflected wave and turns it into an image. The ability of any detector, be it an eye or a camera, to create an image is directly dependent on the amount of available light.
Fig.3. At night there is no sunlight that reflects off all objects, so we are limited to the light of the stars, the moon and artificial lighting. If there is not enough light, it is difficult to see. Cameras with IR illuminators compensate for this by emitting energy that is reflected off everything in the camera's field of view and returns back, creating such an image. Unfortunately, as a result we have serious limitations in range, since reasonably powered IR illuminators are weak and their range, based on the reflection of light energy, is determined by the power of the reflected energy.
Why? Think about it – the energy emitted from these tiny emitters has to travel to the target and back before the camera has a chance to detect it. Unfortunately, the poor emitted photons simply don’t have a chance to travel more than 150m. By the time they reach the target, they’ve suffered enough and simply disappear into the ether. (By the way, if you installed IR floodlights powerful enough to work as thermal imagers, you could turn your business into a microwave oven.)
Like your eyes, IR illuminators work by detecting reflected light. Just like your eyes, IR illuminators will have a better picture if the object you are watching contrasts with the background. If the object does not contrast, you cannot see it. Do you know another word for this? Camouflage. That's right, camouflage essentially reduces the visible contrast between an object and its surrounding background.
Thermal imagers don't have any of these drawbacks. First, they have nothing to do with reflected light: they see the heat of everything on our planet (Really!). Everything you see in your daily life creates thermal energy — day and night, good weather or bad. Just think about it: you are sitting here reading this article, and at the same time you are creating a beautiful thermal image of yourself.
Thermal images of people, cars, buildings and other objects have even greater contrast at night than during the day. During the day, thermal imagers just work and do their job by seeing the smallest temperature differences on objects, and at night they work just fine. So now you know that not all cats are gray at night!
So, what have we learned today? We have learned that night vision devices and cameras with IR illuminators have serious limitations in terms of range, and this applies to all such products, since they are based on the perception of reflected light radiation. We have also learned that these cameras work the worst, actually, when we need them most — at night! Thermal imagers, on the other hand, do not depend on lighting, work by receiving thermal radiation and work best when we need them most.
And finally, most importantly, we have learned the main word that describes an object without thermal imagers guarding its perimeter — «target».
Part two. Every player is different.
Thermal imagers have currently become very popular among video surveillance professionals, as their cost has been steadily decreasing, allowing them to solve complex problems with very high efficiency and a high cost/efficiency ratio.
However, not all thermal imagers are the same, and there are a number of important features that need to be taken into account when choosing equipment, along with the standard approaches used when choosing video surveillance equipment. Let's try to figure out what's what, consistently analyzing what the market currently offers, taking as a basis the fundamental provisions of thermal imaging theory and the common sense of the buyer and integrator.
Existing thermal imagers and systems with thermal imagers can be divided into the following classes:
• Stationary thermal imagers
• Rotating thermal imagers
• Multi-channel rotating systems
Before considering the designated classes of devices, we will outline some theoretical provisions that will help evaluate the quality of the thermal imaging channel as such, and then, on this basis, we will evaluate the finished products.
A thermal imager, like other optical-electronic devices, consists of 3 main blocks: a lens, a matrix, and an electronics block. Thermal imager lenses are made of germanium, since this material transmits long-wave IR waves, can be machined, and is strong enough to work in security systems.
What are the main parameters of a thermal imager that you should pay attention to? Is the lens athermal and its aperture ratio. If the lens is athermal, then the image will remain in focus when the ambient temperature changes. Aperture ratio. This is more complicated. A more aperture lens will provide a contrast image with a not very sensitive matrix, but a less aperture lens will provide a greater depth of field. Matrix. Here you need to look at the resolution, sensitivity, detector material, the presence (it is better not to have it) of a thermoelectric cooler, the operating temperature range. At the moment, the de facto standard for the resolution of thermal imager matrices is 320×240 pixels. However, there are cameras with a resolution of 160×120 or 640×480 and even more, 640×480 matrices are not very common due to their very high cost, and 160×120 matrices are almost never used (although they are sold) because they provide images of obviously worse quality than matrices with a resolution of 320×240 at a comparable cost. If a 160×120 thermal imager is significantly cheaper than a 230×240 device to provide the required range, then this is also a suitable option. Note that the specified input data on matrix resolutions apply to uncooled matrices (microbolometers, ferroelectrics). Cooled matrices and «rulers» are a separate class.
Stationary thermal imagers.
Selection criteria: Sensitivity, matrix resolution, choice of lenses, performance class, connection and control interfaces, operating and storage temperature ranges.
Let's describe a thermal imager that would be ideal for our Russian conditions. Sensitivity — the more sensitive, the better. The best models on the market provide a sensitivity of about 0.035ºС. Resolution — at least 320×240 pixels. No thermoelectric cooler. Athermal lens. Operating temperature range for the middle zone is -30 … + 50ºС, for the northern and eastern parts of the country — -50 … + 50ºС. Particular attention should be paid to the storage temperature, since thermal imaging detectors are sensitive to the effects of negative temperatures and they degrade when stored in conditions below the rated ones. The widest temperature range is possessed by devices on vanadium oxide matrices — VOx (-50 … + 80ºС). The device must be supplied in a casing, since standard casings for thermal imagers are not suitable due to the fact that glass for a thermal imager is like a mirror for a video camera. Thermal imagers use special input windows that transmit the long-wave IR range. If the thermal imager has control capabilities, then standard interfaces and protocols must be supported, such as RS422/485 and at least Pelco-D, as one of the most common protocols. The most responsible manufacturers supply turnkey solutions, where installers only connect the connectors on the thermal imager, without the need for R&D to find special casings and interface converters.
Rotating thermal imagers.
Selection criteria: Thermal imaging channel – the same as for stationary thermal imagers. Pan/Tilt device: if a complex thermal imager-pan/tilt device system is selected, and not just a stationary thermal imager that the user has installed on a familiar pan/tilt device, then most likely there are requirements that are difficult to meet using standard pan/tilt devices. These may be rotation angles, rotation speed, positioning accuracy, minimum rotation increment. As a rule, the entire system is subject to requirements for video control and transmission. It is better to give preference to systems that implement standard PTZ device control protocols, and the pan/tilt device has slip rings, which allows creating systems without a bundle of wires running from the bottom of the pan/tilt device to the thermal imager. Integrated thermal imager/video camera/pan/tilt device systems are becoming increasingly popular. Here, the zoom capability of the video camera should be added to the listed requirements, as this increases the tactical capabilities of the system. For example, a thermal imager can detect something at a great distance, and the video camera zoom lens can zoom in on this object to detail the image. In fact, a video camera without a zoom lens on a rotary device raises serious doubts about its effectiveness throughout the entire operating area of the system.
Multi-channel rotary systems.
Multichannel PTZ systems are systems with two or more optical channels on one PTZ device. Typically, this is a thermal imager and a video camera with a zoom lens, to which can be added: a laser rangefinder, a low-level channel, an active-pulse channel. In most cases, such systems are equipped with cooled thermal imagers installed on specialized PTZ platforms that combine high rotation speed with low, high positioning accuracy with high load capacity, and the most advanced systems include a control and digitization/video compression server. This is an extremely interesting class of devices and we will consider them in more detail in the next publication.
In conclusion, I would like to say that thermal imagers have already entered the circle of technical means that have begun to be actively used to organize video surveillance and perimeter protection of objects. And this is just the beginning. The snowball has just started rolling down the mountain and it will be here soon!
Karneev Dmitry Vladimirovich
Head of the Security Systems Department
OJSC Pergam-Engineering