The Night Challenge.

Considering that special forces often have to carry out their missions under cover of darkness and one of their primary functions is observation, night vision equipment is of paramount importance to them. Yet there are few night vision devices currently produced specifically for special forces, although several items seem to be eminently suitable.

As with many other items of equipment, special operations services -- particularly outside the United States -- have to take their choice from what is available, and that covers a wide field.

Current vision devices rely on one of two base systems, image intensification and thermal imaging. Both are widely employed, the image intensification technique being widespread and relatively inexpensive.

Image Intensifiers

Image intensification is a technique that relies on amplifying available light, for even on the darkest night there are few instances when there is no ambient light to be utilised, such as starlight.

We are now in the third and fourth generation of image intensifiers following the introduction of what are known as channel plates that provide better all-round image resolution.

No matter what intensification generation is involved, two assets are inherent:

* one is that image intensifiers require very little power, supplied by small commercial-pattern batteries.

* the second is the constant miniaturisation of electronic components means the circuits for these devices can be compressed into small confines, and small usually means light.

The latest innovation, also available with thermal imagers, is that the image displays can also be connected to video cameras, allowing images to be transmitted to others in the local team or to commanders at remote locations. Image intensifiers, like thermal imagers, can also be used in weapon sights as well as general night vision applications.

Without going too far into the details of how they operate (this will soon be the subject of an in-depth report in Armada International) it might be useful here to give an overview of their principle to understand what differentiates Gen III from the upcoming Gen IV.

Very schematically, a Gen III tube operates as follows: available photons strike a photocathode plate that in turn generates a proportional amount of electrons. These penetrate a microchannel plate which is in fact a grid of very small tubes that are slightly canted so that the an electron that enters one tube will inevitably hit its sides and will start wiggling its way down, triggering off as many more electrons each time it scores a hit; the triggered electrons will do the same, so a massive numbers of electrons will thus exit the channel plate before striking the phosphor screen that will finally recreate the image -- amplified. The drawback of this system if it were left as described is that the photocathode can be contaminated by the electrostatically discharged ions inside the tube, meaning that a special coating or absorbing film (ion barrier film) has to be applied on the input side of the microchannel plate. A barrier is a barrier, so the US Army Night Vision and Electronic Sensor Directorate sponsored a programme in late 1997 in which both Litton and ITT participated to develop an `unfilmed' microchannel plate-based tube that would last -- the Gen IV tube.

Schematically, the solution retained by Litton was to produce a gated system whereby the photocathode's voltage is turned on and off at rates of about 30 Hz to minimise the contamination effects. Litton's solution was to slave the gating system to an external gating trigger enabling the system to automatically adjust itself to the ambient light, i.e. constantly adjust the requirements on the tube to the actual needs.

As said above, ITT also took part in the development of Gen IV intensification tubes and was awarded a $13 million contract by the US Navy in mid August 2000 to supply 2252 AN/AVS-9 sets fitted with Gen IV tubes. However, as these latest tube generations are not exportable, ITT has introduced what it terms the `Pinnacle' that can be used as a drop-in replacement to retrofit both US and foreign military forces Gen III night vision devices. For the specialists, it provides a signal-to-noise ratio of up to 24 per cent while halo is reduced from 1.25 to 0.90 mm.

Thermal Imagers

Contrary to Image intensifiers, thermal imagers do not require any light at all to operate effectively. They passively detect and process images in the medium and far infrared bands, in frequencies normally associated with heat that are invisible to the naked eye. They can also `see' through haze, dust and smoke as well as being able to penetrate camouflage and some levels of foliage. One asset of the thermal imager is that it can continue to detect where vehicles or personnel have been, even after they have moved away, as the heat `shadows' produced by them can remain detectable for some time. The performance of a thermal imager is directly related to its capability to detect minute temperature differences. One of the authors distinctly remembers the sight of a business aircraft parked one morning at the Dubai Air Show that revealed all its under-skin ribbing of its wings and fuselage: the sun had warmed up the aluminium surfaces but any component that was in contact with them underneath were still slightly cooler.

As usual, there are potential shortcomings. Thermal imagers tend to be larger, heavier and more delicate than image intensifiers and some of them require their sensors to be cooled using compressed gases, with all the attendant logistical difficulties this induces. In addition, during certain weather conditions their image performance can be variable to the point of uselessness. They are also expensive, although their costs are reducing all the time.

Products

Few manufacturers can possibly produce a larger range of image intensifiers than Litton Electro-Optical Systems. The firm produces head-mounted monocular and binocular systems of just about every conceivable kind, shape and form, the latter being available as a true binocular or with a single tube supplying images to both eyes, as well as weapon sights. For many of the Litton products an image intensifier element can have more than one application. For instance, the M983 can be employed either as a monocular or mounted as a weapon sight without the need for drastic modification.

On the other hand, ITT Industries Night Vision says that it has "received more US military contracts for Generation III image intensifier devices since the early 1980s than any other night vision supplier". Turning to exports, the manufacturer claims that "in 1997 alone, the company received two major international contracts: one from Switzerland for $26 million and the other from Australia for $80 million. Each of these contracts exceeded the value of any other international order ever received by the Night Vision division".

In Britain, Pilkington offers weapon sights and observation devices based around the Kite, a small sight unit that can be configured to produce the MaxiKite with increased image magnification and the corresponding Bino-Kite and Maxi-Bino-Kite for observation purposes.

Perhaps the most compact of the image intensifiers come from the Dutch-Belgian Delft Sensor Systems with the Munos (Multiple Use Night Observation System) range. The Munos WS4/6 is the weapon sight version with the image magnification alterable from x4 to x6 by changing a lens element. The Munos OS series has the same facility for x1 or x4 magnification and can mounted on a head harness. To round off the Munos family there is the Mark III, that acts as a x1 weapon sight or head-mounted monocular.

On the thermal imager side, the Raytheon AN/Pas-13 thermal weapon sight is now the standard US Army model in its class and it is reported to have been issued to US special forces. The base AN/Pas-13 weighs in at 1.72 kg so its weight and bulk can make quite a difference to the handling of some rifle-type weapons. There is also a Heavy Model for mounting on heavy machine guns and automatic grenade launchers.

Raytheon has also developed a hand-held thermal imager, the Mag 2400, intended to observe targets at long ranges; it has been procured by the Danish Army. US Special Operations Command has ordered the DRS Optronics Advanced Nightstar binoculars that can also provide target range, azimuth and elevation data to combat computers. A European hand-held night vision equivalent is the Signaal Usfa and Delft Sensor Systems Light-weight Infrared Observation Night sight (Lion).

There are many other image intensifier and thermal imager manufacturers with products that would appeal to special forces but those mentioned above serve as an indication of what is available.

All the devices mentioned above have one thing in common, they all require batteries to operate. In the future, supply quartermasters will not have just food, water, fuel and ammunition to worry about -- they will also have to maintain a constant supply of batteries.