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Whether in combat or during peacetime there are many threats that persist for today’s military helicopters. These threats include hostile acts such as shoulder launched missiles, rocket propelled grenades (RPGs) and small arms fire. They also include degraded visual environments caused by dust, smoke, rain or snow that lead to collisions with other aircraft, power lines or the ground. DRS, along with several other companies, is working to develop infrared (IR) based solutions to protect our warfighters in each of these scenarios.
First, let us address man-made threats. The vast majority of our military’s helicopters have a threat detection suite for detecting missiles based on “seeing” the missile in the ultra-violet range of the electromagnetic spectrum. These sensors have been matured after many lessons learned and many years to provide improved performance, but they are still limited by certain atmospheric and environmental conditions. In particular, there is a fine line differentiating a missile from a “false” UV source (such as a halogen lamp). The UV landscape in any given location, elevation, time of day or season can also affect performance against these “false alarms”.
The advantages of IR over UV for these applications include detection of threats over much longer ranges resulting in more warning time and improved survivability. In the case of the IR solution, the sensors are detecting the heat emitted from the missile motors including the initial ejection from the missile launch tube/vehicle as well as the boost motor on the missile itself. Additionally, IR-based systems are better suited to adapt to emerging threats.
The challenges with fielding IR sensors for broader proliferation in the rotary-wing market have been cost and the harsh thermal environments these sensors must endure. IR cameras utilize cryogenically cooled detectors that have historically required operational temperatures on the order of -320°F to be effective. These coolers and corresponding sensor electronics draw significant power and without a viable thermal path to dissipate that power can self-heat to the point of failure. Improvements are being made to increase the operating temperatures for IR detectors and provide a path to lower power, higher reliability sensors that can operate in these harsh conditions.
Infrared sensors, much like their UV predecessors, contend with many “false” sources in the environment that have to be processed in order to avoid “false alarms” and yet still detect a true threat from an often cluttered view. Leading sources of IR signatures in our environment include industrial sites, power plants and solar reflections. DRS has developed 2-color IR missile warning sensors specifically to address these “false alarms”. By leveraging two different wavelength bands (or colors) of the Mid-Wave Infrared (MWIR) spectrum, these advanced sensors can more adeptly discriminate between a real threat and a “false alarm”. The graphic at the beginning of this article illustrates that the environment and a typical threat look very different in the two different colors and this information can be used in a straightforward algorithm to determine if the heat source has the correct thermal characteristics to be a threat.
In the paragraphs above, much is made of false alarms because in tactical use they add undue stress on the aircrew and much like the boy who cries wolf can cause hesitation when a true threat is realized. The use of IR for missile warning is gaining traction with new program starts on the horizon and the maturation of advanced 2-color hardware and techniques.
There are also exciting advancements in the use of specific regions of the IR wavelength band to allow the aircrew to see through airborne obscurants such as dust. These so-called Brownout conditions are as dangerous to the aircrews as wartime missions and account for nearly half of the aircraft losses during the last decade of conflicts in the Middle East. While the MWIR region of the IR spectrum is optimal for detecting missiles, the Long-Wave Infrared (LWIR) region is better for degraded environments.
In fact, ground vehicles have long utilized LWIR sensors for this very reason. In ground combat you operate in a relatively dirty battlefield with dust clouds stirred by heavy equipment or wind, smoke from munitions or burning vehicles/structures/vegetation and weather. LWIR performs better than MWIR under these conditions as well as in cold weather. While helicopters are less vulnerable to these conditions in higher altitude flight they are subject to heightened risk during landing and take-off. As a result, several companies have been developing large format LWIR sensors to be used specifically to provide pilot situational awareness in these degraded visual environments.
In summary, today’s IR industry is striving to develop state-of-the-art sensors and systems to protect our helicopter aircrews from all manner of current and emerging threats. From hostile fire to environmental conditions, IR technology provides an affordable, multi-function means to increasing surviveability in today’s fiscally constrained environment.