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military and defence
Heat of battle
Greg Blackman explores the various imaging technologies deployed by soldiers on the battlefield
Of the many considerations defence contractors must make when developing devices for soldiers on the battlefield, the so- called SwaP ratio, or size, weight and power of the device, is a crucial one. The device must continue to work even under harsh battlefield conditions – but, for any battery-powered instrument, there is a trade-off between maximising operational life and making it small and light enough for the soldier to carry. ‘The weight of equipment soldiers carry on the battlefield is a real burden,’ comments Marc Larive, marketing manager at infrared detector manufacturer Sofradir. He adds that the total load a soldier might carry could reach 40kg. Sofradir has developed HOT (high operating temperature) infrared sensor technology, which potentially can reduce the size and weight of a cooled IR imager. Sofradir’s HOT detectors operate at a higher temperature compared to standard cooled IR sensors, thereby reducing the power consumption required to cool it. ‘A typical infrared detector has a power consumption around 4W, while HOT detectors
use less than 2W power consumption, which is really important for designing a small system,’ states Larive. Sofradir’s standard focal plane arrays, made with mercury cadmium telluride (MCT) technology, operate at around -183°C, while the HOT Scorpio TV-format MWIR prototype, also an MCT detector, is capable of operating at -123°C and consumes less than 2W of power. Handheld thermal imagers typically operate
in the mid-wave infrared (MWIR), as the power consumption is less than for detectors operating in the long-wave infrared (LWIR). And soldiers still require the range and performance of cooled IR detector technology. Systems used for the targeting and tracking
system onboard fighting vehicles, such as main battle tanks for example, typically operate in the LWIR, however. Sofradir’s LWIR detectors are part of a fire control system, developed by Thales, for the Nexter VBCI, a French Infantry Fighting Vehicle. Sofradir’s subsidiary, Ulis, has also supplied detectors for the vehicle: its uncooled infrared focal plane array is used for panoramic observation onboard Nexter VBCI. LWIR is well suited for fire control systems
as it allows soldiers to see better through dust and particles than in the MWIR. In addition, the blooming effect is less in LWIR than in MWIR, an aspect which is especially important for fire control systems in tanks and other
fighting vehicles. ‘An explosion or something very hot in the field of view can result in saturation of the pixel,’ explains Larive, adding that neighbouring pixels can also be affected to the point where a large part of the image is saturated for the duration of the explosion. This effect is less in the LWIR than the MWIR. ‘Military system developers want higher performance with a greater number of pixels without any significant increase in size of the detector,’ states Larive. ‘The previous generation of LW detectors [from Sofradir] had a pixel pitch of 30µm; current versions have a 15µm pixel pitch, so four times the number of pixels can be fitted in the same sized detector array. These new sensors have a higher resolution and can detect smaller objects further away.’
Eye in the sky SWaP considerations are also important for drones and unmanned vehicles to minimise energy utilisation. A team of engineers from Middlesex University has developed a lightweight unmanned aerial vehicle (UAV) designed to give the soldier a bird’s eye view of the surrounding area via a live video feed. The device is small enough to fit in a soldier’s backpack and Dr Stephen Prior, who led the development team at Middlesex University, comments that the main goal of the project
imaging and machine vision europe october/november 2011
www.imveurope.com
Image courtesy of Dan Peretz/Shutterstock
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