Hohenstein Institute: Invisibility During Daytime And Night-time Military Operations Can Be Tested

BOENNIGHEIM, Germany — October 12, 2015 — Camouflage plays a vital role in daytime and night-time military operations. The use of camouflage prints and special dyes ensures that people and equipment are hard to detect because they blend in with the surrounding terrain.

Since all bodies emit heat, known as infrared radiation (IR radiation for short), it is now possible with the help of thermal imaging cameras to “see” people even in complete darkness. In connection with this, the Hohenstein Institute in Boennigheim uses a spectrophotometer to test the chromaticity (colour saturation) and IR reflectance of various textile materials as used, for example, in desert or multi-terrain combat suits.

The institute has also developed textiles as part of a research project which provide effective screening against infrared radiation and are of interest for use in uniforms for the armed forces.

Daytime Operations: Improving The Optical Camouflage Effect
Military combat suits are usually made using the standard camouflage patterns of 3-5 colours in shades of brown and olive green. In daylight, these camouflage prints, when perfectly matched with the terrain, enable users to “melt” into the background and so protect them from being seen by the enemy. When white light such as sunlight falls on the uniform, certain parts of the light spectrum are absorbed and others reflected.

This is why the uniforms (and objects in general) appear multicoloured. Because the human eye can distinguish between over 350,000 different shades, colours have to be measured with a spectrophotometer. The colour measurement process investigates which parts of the white light are reflected by the sample of material that is being tested. These are measured statistically so that any deviations from the colour specifications can be identified. That is the only way to ensure that the colours in the camouflage pattern meet the technical requirements. The optical camouflage effect is tested when the textiles are new and after artificial ageing, using spectrophotometric colour measurement in accordance with DIN EN ISO 11664 and DIN 5033.

Night-time Operations: Effective Screening From Infrared Radiation
Night-time operations are a challenge not only for the soldiers but also for their clothing. Special materials ensure that the revealing infrared thermal radiation (IR radiation) produced by the warmth of the soldiers’ bodies is absorbed. That is why infrared-absorbing inorganic or organic pigments (special vat dyes) are
used for the camouflage prints on uniforms, to ensure that the wearers are largely “invisible” to the CCD sensors on night-vision devices. The Hohenstein Institute uses spectrophotometric reflectance measurements to test whether the maximum reflectance limits comply with the regulations (e.g. technical terms of delivery).

However, these dyes only cover short-wave infrared radiation. With the help of thermal imaging cameras which also capture long-wave infrared radiation, a person’s thermal signature can still be visible despite the special vat dyes. The Hohenstein experts wanted to counteract this effect and so as part of a research project (AiF-No. 15598) they developed some new materials. The textiles were impregnated or coated with chemical fibres containing indium tin oxide nanoparticles (ITO). ITO particles are transparent semiconductors that are familiar from their use in touchscreens and smartphones. The innovative textile finish ensures that the person’s thermal radiation is absorbed far more effectively, while the same level of wearing comfort is maintained.

Just how effectively the soldiers’ uniforms make them “invisible” during night-time operations can be tested by the spectrometric measurement of radiation absorption, reflection and transmission under DIN EN 410 that is carried out at the Hohenstein Institute.

Extensive Expertise Available To Support Military Users
In addition to its spectrometric testing of the effectiveness of camouflage materials for use in daytime and night-time operations, the Hohenstein Institute also offers other services that can be extremely useful to the armed forces in their work. These include testing the fit, skin-friendliness and comfort properties of items of uniform, since these have been shown to affect the mental performance of the soldiers. The institute also carries out testing for harmful substances in accordance with OEKO-TEX® Standard 100 and anti-insect protection testing, to prevent any risk to the soldiers’ health.

Posted October 16, 2015

Source: Hohenstein Institute