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By David Maxwell

We have described the spread of airborne electro-optic/infrared (EO/IR) sensor turrets sensors used by unmanned aerial vehicles (UAVs) in previous issues of Battlespace. This feature will look at some of the latest sensor configurations and what they bring to the overall ISR (Intelligence, Surveillance and Reconnaissance) user community.

One of the benefits of on-going operations is that armed forces tend to realize that some equipment they have in service may not be quite as capable as they could be and, thus, either new kit is procured or existing kit is upgraded. This is usually via some form of what the UK refers to as an Urgent Operational Requirement (UOR). Such procurement has become more evident in the UAV field.

A year ago, in June 2011, Raytheon Space and Airborne Systems revealed that it had received a contract from the US Air Force (USAF) to develop a hyperspectral detection system for UAV applications. Known as the AN/DSQ-68 Airborne Cueing and Exploitation System Hyperspectral (ACES HY), the company was producing an evaluation batch of nine units to be fitted to USAF MQ-1 Predator UAVs in an under-fuselage mounting, aft of the standard AN/AAS-52 Multispectral Targeting System-A sensor turret. It is assumed that some of these have now been delivered, installed and have been or are still under evaluation.

Beyond the fact that it builds upon earlier work undertaken by the company for the US Environmental Protection Agency, Raytheon has revealed little of the detail involved. Hyperspectral sensors, using the different reflectivity properties in the sub-bands across the IR spectrum, already exist as space-based systems. They are used to detect different types of ‘targets’, such as the presence of chemicals or disturbed earth, based on their spectral characteristics. According to Raytheon, ACES HY is the first time that hyperspectral technology has been brought ‘closer to the ground’ in a UAV application. It is a reasonable speculation that ACES HY is being applied in the Counter-Improvised Explosive Device (C-IED) role.

Perchance, the up-coming Eurosatory exhibition (in June) or the Farnborough air show (in July) will reveal more on this programme. However, what this does illustrate is that users are becoming more conversant with the application of the infrared spectrum and the way in which greater attention to specific areas can reveal more detailed information of value, or create a better image.

Of particular note has been the introduction, over the recent past, of Short-Wave InfraRed (SWIR) detectors, operating in the 1.4 to 3 micron range allows the generation of images in darker conditions. Operating on a wavelength band that carries more photons at night than does the visible wavelength, SWIR detects reflected light at wavelengths that are invisible to the human eye, and that reside in wavelength bands between visible and traditional thermal ranges of Mid-Wave InfraRed (MWIR – 3 to 8 microns) and Long-Wave InfraRed (LWIR – 8 to 14 microns) .

SWIR offers the user not only the traditional ability to see at night but also in poor atmospheric conditions. Additonally, it can also see many of the battlefield lasers used for targeting, such as those used for laser range-finding or to mark targets for laser-guided munitions.

Among the several companies producing SWIR cameras, Raytheon notes that its SWIR camera uses indium gallium arsenide (InGaAs) detectors, both the current ultra-low dark-current models circuits. Both FLIR Systems/Government Systems and L-3 Wescam offer SWIR cameras as part of the sensor suites for various models of their turret systems.

The advantage of using another part of the spectral range is that images can be blended together to form a composite picture, showing the best elements of each in a ‘fused’ image. This subject has been dealt with on these pages before both in relation to airborne sensors and, also, to infa

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