An Cosantóir

www.military.ie THE DEFENCE FORCES MAGAZINE | 15 ORDNANCE CORPS ARTICLE SERIES - HOW YOUR EQUIPMENT WORKS BY ORDNANCE SCHOOL, DFTC T he ability to fight at night is of great importance to mod- ern military forces. The lack of visible light at night affects the soldier's ability to observe friendly troop movements, understand terrain, and affects perception of enemy movements and positions. DF personnel have two technologies at their dis- posal to assist them to operate in low-light environments: image intensification and thermal imaging. To understand these technologies, we must understand electromagnetic radiation, which refers to waves propagating through space at the speed of light carrying electromagnetic energy. Visible light, radio waves, microwaves, infrared, ultra- violet, X-rays and gamma rays are all forms of electromagnetic radiation, differing by frequency and wavelength. Our eyes have adapted to seeing the small portion of this spectrum (0.4 - 0.7µm) that corresponds with the most intense radiation emitted from the sun. However, in the absence of visible light we can use technology to take advantage of non-visible sources of electromagnetic radiation. The most well-known technology is image intensification, or night vision, which works by amplifying available light in the visible and near-infrared (0.7 - 2.5µm) spectrums. At the heart of the system is the image intensification tube. First designed in the 1960s, this device has undergone several generation changes but still relies on the original concept, in which available photons of light strike a photo-emissive surface, or photocathode, at the front of the tube. These are converted into electrons that are then amplified along the tube using high voltage and a micro-channel plate. The amplified electrons strike a phosphor screen at the back of the tube where their energy is converted to photons that create a visible green image of the area. Image intensifiers are passive systems but can also detect ac- tive, non-visible infrared sources to improve imaging and lasers. Passive sources like IR paint, tape and patches, along with active sources like IR beacons and 'chem lights' allow identification of friendly forces through image intensifiers, helping to avoid blue- on-blue incidents. Image-intensification equipment available to DF personnel include the Thales LUCIE night-vision goggles and the KITE weapon- mounted sight for the Steyr and FN MAG. In contrast to image intensification systems that use reflected energy, thermal imag- ing depends on emitted energy. All ob- jects with temperatures above absolute zero (-273 o C) emit electro- magnetic radiation, with the emitted wavelength directly related to the object's temperature. For example, a fighter jet's exhaust plume will emit radiation in the near IR and visual spectrum, while humans and vehicles emit radiation in the far IR (8 to 14µm). To produce a thermal image the small temperature differences observed by the detector are converted into a visual picture that is equally effective by day or night. The thermal imager lens, typically made of germanium, focuses the object's emitted radiation onto a phased array of infrared detector elements to produce a tempera- ture pattern, which is then displayed in colours proportional to the intensity of the infrared. Two types of IR detectors are used in thermal imaging: thermal and photon detectors. Thermal detectors, such as the Kongsberg RWS Protector, do not need to be cooled and conse- quently are small, light weight, and provide output on start up. Photon detectors, which use multiple semiconductors, have much higher response time and sensitivity compared to thermal detectors, but must be cooled. The FGM-148 Javelin anti-tank missile system and the FLIR B2-FO RECON both use photon detectors. Troops from 2 STA BTY, 1 BAR on a patrolling exercise in Kilworth. Photograph taken using the FLIR B2-FO RECON, a key component of the new artillery OP suite. Kongsberg M151 Protector RWS (remote weapon station) mounted on a Mowag Piranha in UNIFIL. Note the bottom mirror-like lens belonging to its thermal imager. ARW operators during Exercise 'Ullamh'. Note the dual, helmet-mounted NVE and weapon-mounted visible/IR light and laser.

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