Drilling the darkness.

The ability to see, and therefore fight, at night has revolutionised warfare. Those endowed with the required equipment definitely had an edge, but night vision systems are becoming more affordable and thus available to 'both sides'. A difference remains, though, and that is the performance of the systems depending on the age of the technology on which they are based.

Compared with the more traditional methods of fighting, the ability to be operational 24 hours a day also brings about an acute problem in that it requires a level of logistics that is able to follow troop movements. This is not the theme of this article but is perhaps worth mentioning in passing, as this aspect should not be overlooked.

There are two distinct methods of drilling some vision into the darkness. One is light intensification, the other infrared vision. In fact, a third method is now emerging, called image fusion, which, as the name implies, merges what is seen by the two aforementioned types of devices in an attempt to mutually compensate their intrinsic shortcomings. This is a very specific subject for the time being and will be examined in a dedicated article in Armada issue 4/2005.

Light Intensification

The objective of light intensification, as its name implies, is to capture whatever light is available and amplify it. In the first generation of systems the principle is in fact very close to that of a sound amplifier. The light particles, called photons, are converted into electrons as soon as they hit a photocathode tube; their numbers are multiplied and then sent to hit the back of a fluorescent screen where they regenerate the image. This is how the first generation works, and is known as Gen I. Like the old amplifiers though, they create distortion if one tries 'to turn the volume up' too high.

Enter Gen II. To reduce the fuzzy effect, someone had the idea of introducing a device called channel plate with a view not only to keep the electrons under a certain directional discipline, but also to enable then to literally multiply themselves. The channel plate is a disc pierced with myriad tiny tubes (the channels) through which the electrons are forced to travel, but in doing so, still hit the walls of their respective tubes as they wiggle their way down and generate a second electron as they do so. The more ordinate and powerful stream of electrons offers a sharper and brighter picture.

Gen III came along to solve yet another problem. As the 'volume button' is turned up again, the surface of the microchannel plate gets quickly polluted with drop out material that again fuzzies up the picture (but we are still at a very high improvement level over Gen I). To reduce this effect, a gallium arsenide film is deposited on the surface of the microchannel plate. To offer a very gross comparison, this has the same effect as using a Teflon frying pan: it stays clean, but as with the pan, it deteriorates with time and usage, as the author was able to once witness.

Gen IV is also known as 'gated filmless'. Filmless is easy to understand, it means that the film is gone. So gated? This simply means that the source of electrons is interrupted and switched on again at a frequency that is so high that it is not perceived by the eye. By doing this, not only a cleaner picture is generated, but also the life of the microchannel plate is preserved--and so is that of the battery, by the way. Basically, it is the same technique as used in modern diodeemitting light torches: the light is crisp and bright, but the eye never realises that the torch is actually switched off half of the time or more. Another advantage of the gating technique is that it enables a much faster reaction to varying external light levels.

Even if budget is no question, acquisition is not only a matter of price. While Gen I systems are now available at sports and hunting shops (and even on the Internet), Gen II are also available but are also far more expensive and generally used by police forces. Gen III, sorry, only to US and Nato forces, and in the latter case with certain restrictions. Gen IV is "US only".

It goes without saying that the better the amplification, the better the visual range, since multiplying lenses can be adapted (photographers in particular shall appreciate the meaning of this).

Infrared

In total contrast with light intensification, the infrared technique does not try to work from an existing picture, but builds one from the varying temperatures that constitute a scene in very much the same way that a hand can make the difference between hot and cold water. In our education, our brain interprets red and blue respectively--although an infrared sensor will translate this in a monochromatic way as bright and dark. In other words, a black panel in a snowfield is more likely to be seen as white because it is warmer, but the snow will be black.

The operating principle of infrared is theoretically simpler than that of light intensification, but requires more powerful peripherals, as one would now call them. Basically, one can compare an infrared camera with a normal digital photo camera in which the sensor would be replaced by a plate that is sensitive to rays that the eye can no longer see because they are well below the red end of the electromagnetic spectrum. The beauty of an infrared camera is that, conversely, it will not see what the human eye will. In other words, the camera will not be dazzled by the light of a normal vehicle headlamp. Yes, by now you will have also understood that the downside is that it can be dazzled by special high intensity flares or lamps radiating in the infrared spectrum, but on the other hand, and under normal conditions, an infrared camera will enable its user to see certain things that cannot be seen, including in daylight. For instance, a stopped vehicle at a distance: has it just parked or has it been there for hours? The brightness of the bonnet will very simply provide the quick answer.

In terms of image quality and camera performance (and except for details that will be described in the future article mentioned above), a straight comparison can be made with today's digital cameras: crucial are the sensitivity of the sensor (contrast) and density of its elements (resolution). The contrast level is very important, as the ability of a camera's electronics to perceive a difference of less than a tenth of a degree at an ambient temperature of 30 degrees can be rated as pretty good.