Infrared countermeasures: a point of view.
There is an increasingly widespread employment of optical and IR guided weapons around the world. We in the United States in particular are applying EO/IR sensors to more and more of our weapons. This trend has been made possible by significant advances in EO/IR sensor technology - both in performance at reduced cost and in the signal processing capacity necessary to make such systems practical. The long-held myth that EO/IR weapons can only function in good weather has in many cases been dispelled. Many recent tests have demonstrated' that EO/IR sensors operate far better than expected in humid, cloudy and wet conditions. Furthermore, advances achieved in the fabrication of IR focal plane arrays will provide an inherent resistance in missile systems facing the most extensively used IR countermeasures - flares. We can expect our adversaries to experience a parallel growth in IR technology and the attendant deployment of advanced sensors possessing IR imaging capabilities. The emergence of hostile weapons with IR imaging abilities will pose a unique and severe challenge to the EW community, because conventional IR countermeasures will be ineffective against this class of seekers. We will need to harness the combined power of IR imaging systems with lasers to defeat future generations of IR missile threats. However, before addressing advanced technologies, a brief look at some of the past and current EO/IR developments is appropriate.
When the space shuttle Columbia first roared off into space April 12, 1981, many of us sat comfortably in our living rooms watching this momentous event on television, not fully aware of the miracle of optical tracking taking place before our eyes. Clearly visible, and legible at 20 miles, were the NASA markings on the side of the space vehicle. While we have come to expect such marvels as commonplace, they serve to demonstrate how far we have advanced in our ability to use precision optics to track missiles at long ranges.
Since the Columbia launch, developments in optical and IR sensing technologies have been progressing at a staggering pace. Innovations in IR sensing materials, coupled with improved optics and associated signal processing are occurring almost daily, with a profound impact on the performance of EO/IR systems.
Some of us may not fully appreciate the impact of IR guided weapons in modern warfare. While most of us are aware of the spectacular history and effectiveness of the Sidewinder air-to-air missile in combat because of the extensive television and print news coverage, many believe that RF guided missiles have accounted for the majority of kills on hostile aircraft in recent years. However, such is not the case. Originally published in 1985 in a DOD/AOC study on IR countermeasures) clearly illustrates, in the time period between 1979 and 1985, 90% of all known aircraft losses were attributed to IR missiles ! Note that in action over the Bekaa Valley in Lebanon, Israeli aircraft using AIM-9G/L air-to-air, heat-seeking missiles downed 89 Syrian MiG aircraft in one day's fighting! If we were to update this chart by adding the number of Soviet helicopter kills attributed to the Stinger missile used in Afghanistan, the percentage of aircraft killed by an IR missile would increase to greater than 95%. It has been reported that from the introduction of the Stinger missile in Afghanistan in 1987, an average of one Soviet helicopter was destroyed for each day of the war thereafter. The bottom line is clear - in spite of the criticism that IR weapons are only effective in good weather, during the past 11 years, the weather has been good enough for IR missiles to destroy more than 95% of all aircraft downed by missiles and gunfire ! But this message has not been lost on the suppliers of weapons for the world's armed forces. The new generation of weapons is bursting at the seams with EO/IR sensors and guidance systems. Consider the massive use of night-sights for foot-soldiers, the extensive use of IR night-vision devices on tanks, the employment of FLIRS on LANTIRN, the guidance system on the IR Maverick, the use of IR guidance techniques on the ADATS and the AWS-M - just to name a few. The reason for this is clear: EO/IR sensor technology produces the ideal weapon in a world where the complexion of warfare is dramatically changing.
Certainly no one would argue with the prediction that most future military engagements will be limited to low intensity conflicts in various hot spots around the world. Such engagements will place a premium on the flexibility and intrinsic covertness offered by EO/IR sensors. The nature of low intensity conflicts often ensures they will occur in areas and over terrain where line-of-sight weapons are essential, or night operations are desirable and this is precisely where EO/IR weapons are best. Even in areas where poor weather conditions exist, IR sensors have performed well.
STARING THROUGH THE FOG
Recent tests have begun to dispel the myth that IR sensors only perform well in good weather. A headline in the November 20, 1989 Defense News reported, "ADATS Works in Adverse Weather, Tests by Industry Team Conclude." The ADATS using its laser in conjunction with TV camera or forward-looking IR sensor, consistently tracked and hit aircraft and missiles flying in rain, snow, fog and freezing drizzle. Tests such as these and many others are graphically demonstrating that emerging EO/IR sensors can operate in inclement weather conditions. However, if one single advancement in IR sensors could be named which will revolutionize the future course of IR weapons, it would certainly be the emergence of the IR focal plane array (IRFPA).
These postage stamp sized arrays contain tens of thousands of IR detector elements called "pixels." When an IR scene is focussed on the IRFPA, the scene information on each pixel can be rapidly read out to a signal processor, where the IR scene can be inspected to detect and track targets such as enemy tanks or missiles. The ability to use high-speed processors to pick targets out of noisy backgrounds is a formidable task which needs continued improvement in R&D, but significant progress is being achieved.
Another advantage of the IRF-PA is a "staring" device and hence has no mechanically moving parts such as scanning mirrors used in Infra-Red Search and Track Sets. Hence, it is intrinsically rugged, reliable and suitable for operation in high-vibration environments. Since it is a staring device, the IRFPA actually "sees" or creates an image of the scene much like a television. It therefore can be much less susceptible to conventional IR countermeasures (such as flares) because of its visual ability to discriminate between targets and flares.
There is an even better reason for employing IRFPAs - with its signal processor, the device promises a solution to the problem that has historically been the bane of IR sensing systems: high false alarm rates. Because IR systems must pick up targets of interest from backgrounds containing thousands of possible IR signals (e.g., sun reflection off clouds and water, hot smoke stacks, fires, explosions, etc.), they often mistake background reflections and emissions for real targets. Obviously, high false alarm rates are intolerable, and hence many previous IR systems (warning systems in particular) were unusable in combat conditions. However, the IRFPA promises to solve this problem, since by virtue of "staring" at the IR scene, its processor can employ temporal, spectral and spatial processing to help eliminate false alarms and pick valid targets for tracking.
Why then, with all of these advantages, have IRFPAs not seen wider application in military systems? The fundamental problem has been their high cost, brought on by the difficulty to produce large quantities of IRFPAs with high yield. Today, an IRFPA composed of a 64 x 64 element array of indium antiminide detectors typically costs in the neighborhood of $50,000. Larger arrays cost even more. Stated another way, in 1986 dollars the average cost per pixel was about $10. At this cost, IRFPAs were unaffordable for most military systems, and this has placed the DOD on the horns of a dilemma.
In 1986, the under secretary of defense requested the DOD product Engineering Services Office (DPESO) to assess the requirements for IRFPAs in military systems. DPESO reported that more than $10 Billion of R&D was planned for systems requiring IRFPAs during fiscal 1988 1992 as shown in the accompanying chart. Although no longer accurate, the chart does indicate the magnitude of the potential for IR focal plane arrays.
DPESO further estimated that the combined needs for IRFPAs in military systems between 1991 and 1996 totaled more than 340,000 IRFPAs (based on a 64 x 64 element array). A back of the envelope estimate quickly showed that at a cost of $10 per pixel, about $14 billion would be necessary just to purchase the needed arrays! These astronomical cost projections led the Office of the Secretary of Defense to initiate a producibility program aimed at significantly reducing the cost of IRFPAS. The program was named the "Infrared Focal Plane Array Initiative."
After a stormy beginning, during which the fate of the IRFPA initiative was debated by Congress, the program was finally started in 1989 with limited funding under the direction of DARPA. Three companies - Rockwell, Hughes and Fairchild were placed under contract to develop low-cost IRFPAs fabricated from three detector materials (InSb, HgCd Te, PiSi) aimed primarily at tactical applications. The goal of the IRFPA initiative is to reduce the cost to 0.10 per pixel, thereby reducing the price of a $50,000 array to $500. These new low-cost IRFPAS, when they become available, will give rise to a whole new generation of highly sophisticated and capable IR sensors and weapons.
But we must be wary, lest we become mesmerized into believing we are the only nation engaged in the pursuit of IRFPA technology. Other countries, most notably Japan and France, are also competing to produce affordable IRFPAS. The French government, for example, has sponsored SOFRADIR to establish a plant at Grenoble, France, dedicated to the production of low-cost IRFPAS. Current plans are for SOFRADIR to produce 100,000 IRFPAs for the sensors in the European anti-tank missile called TRIGAT.
Hence, we can readily conclude our adversaries will also soon be developing IRFPAs for their own use in future IR missiles and other weapons. Since IR missiles and sensors using IRFPAs are essentially immune to current-generation IR countermeasures, the challenge to us is clear if we wish to maintain our technical superiority in IRCM.
THE EO/IR CHALLENGE
We must aggressively pursue an accelerated program to address the severe problems posed by hostile weapons employing IR imaging sensors. Further, if we expect to be successful in the quest, we should harness the power of the laser to blind the new class of sensors. Certainly in the interim period, we must upgrade our existing IR countermeasures and can no longer rely on conventional free falling flares. We must accentuate the development of flares that exhibit realistic spectral emissions and possess aerodynamic flight characteristics which confuse hostile missiles that may employ flare rejection capabilities.
Regardless of the approach taken, the first order of business in defeating IR missiles is acquiring the capability to reliably detect an attack by SAM and air-to-air IR missiles. We do not do this job well. However, the service laboratories have two important programs addressing the missile warning problem. The Avionics Laboratory at WRDC is pursuing a scanning system named "SAWS," and the Naval Research Laboratory is capitalizing on the potential high pay-off of IRFPAs in a system named "Fly's Eye."
However, to realize the capability of missile warning systems employing staring IRFPAS, the ability to process the enormous amount of data from the focal plane must be achieved. For example, a typical 128 x 128 element focal plane array has 16,384 pixels. If the staring array is sampled 100 times per second and each pixel is digitized to 10 bits, this represents a data rate greater than 16 million bits per second. The number of computer operations necessary to perform temporal, spectral and spatial filtering and track IR targets can easily exceed 1 billion operations per second. The job of building such processors to match the constraints of tactical aircraft poses a formidable challenge and deserves high priority.
Finally, perhaps the most difficult challenge remaining is the development of efficient, low-cost, solid-state lasers and their associated pointing and tracking systems. The challenge is in the development of a relatively high power and affordable source of laser energy. Efforts are underway in the laser community to achieve this goal, with diode pumped, solid state lasers appearing to be the optimal solution.
In summary then, it is clear that EO/IR-guided weapons are becoming increasingly prevalent and capable in today's military scene. More than 95% of all aircraft losses to missiles and guns in the past 12 years have been caused by IR missiles. The United States is embarking on an intensified effort to produce affordable IRFPAS. The Japanese and French are also running well in this race, and we can expect our adversaries to develop and exploit IR guidance systems employing IRFPAs as well. IRFPAs will form the basis for developing IR missiles that are highly resistant to conventional IRCM. We must take the necessary steps now to accelerate the development of the technologies to produce IRCM techniques capable of countering IR imaging missile guidance systems. To accomplish this objective we should expedite our work on missile warning systems employing the emerging IRFPAs and their signal processors, and on technologies to develop low-cost, solid-state lasers with their associated pointing and tracking systems.
We have the technologies to build and field a new generation of advanced IR countermeasures, but we should not procrastinate in this quest. A thoughtful sage once said:
There are two things, which, when taken in small measure are good, but when taken in large measure are intolerable: salt and hesitation.
Let us not hesitate in the work we must accomplish to protect our military systems from the future generation IR missiles.
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|Title Annotation:||guest editorial|
|Author:||Nicholas, George; DeMonte, Vito|
|Publication:||Journal of Electronic Defense|
|Date:||Apr 1, 1990|
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