NATO-SCI-139 and its predecessor groups have more than a decade of history in the evaluation and recommendation of EO and IR Countermeasures against anti-aircraft missiles. Surrogate Seekers have proven to be a valuable tool for this work. The use of surrogate seekers in international co-operations has several advantages over the use of an operational seeker, which is in service or in development: 1) the system is flexible, allowing both hardware and software modifications to be made in order to test the effectiveness of specific IRCM techniques; 2) the seeker design is openevery last parameter is available to the science team, allowing detailed, end-to-end validation of software models and simulations; 3) the availability of an unclassified seeker facilitates open discussions on CM issues between the participants in the NATO-group. Testing of high intensity countermeasures (for example based on lasers) needs a system with realistic seeker optics, with proper representation of optical scatter in seeker optics, which differs from scatter in commercial infrared camera optics. A technical description of the ISS is given: an overview of the optical design and the detector, the principle of the tracking software and the possibilities to implement alternative tracking algorithms in order to represent different threat CCM techniques. The ISS is built for use both in the laboratory and in the field. Finally, some experimental results will be presented.

ABSTRACT

There are many weapon systems in which a human operator acquires a target, tracks it and designates it. Optical countermeasures against this type of systems deny the operator the possibility to fulfill this visual task. We describe the different effects that result from stimulation of the human visual system with high intensity (visible) light, and the associated potential operational impact. Of practical use are flash blindness, where an intense flash of light produces a temporary "blind-spot" in (part of) the visual field, flicker distraction, where strong intensity and/or color changes at a discomfortable frequency are produced, and disability glare where a source of light leads to contrast reduction. Hence there are three possibilities to disrupt the visual task of an operator with optical countermeasures such as flares or lasers or a combination of these; namely, by an intense flash of light, by an annoying light flicker or by a glare source. A variety of flares for this purpose is now available or under development: high intensity flash flares, continuous burning flares or strobe flares which have an oscillating intensity. The use of flare arrays seems particularly promising as an optical countermeasure. Lasers are particularly suited to interfere with human vision, because they can easily be varied in intensity, color and size, but they have to be directed at the (human) target, and issues like pointing and eye-safety have to be taken into account. Here we discuss the design issues and the operational impact of optical countermeasures against human operators.

Reduction of the infrared signature of warships helps to increase their survivability. Two methods to reduce the infrared signature are discussed: the cooling of exhaust gases and the application of low emissivity paint. The infrared signature of a generic frigate has been calculated with and without signature reduction. The signature values are used to determine the lock-on range of four generic infrared seeker heads of anti ship missiles ranging from hot spot seekers to imaging seekers. From the reduction in lock-on range the reduction in hit probability is calculated. The results show that both exhaust gas cooling and low emissivity paint contribute to the survivability of a warship.

In recent years, much advance in the field of high-power femtosecond laser technology has been made. The high pulse power of femtosecond laser systems leads to various interesting phenomena, such as a very high power density and the formation of a plasma in the propagation medium, which is usually air. The possible application of femtosecond lasers for infrared countermeasure (CM) applications, other than direct illumination of the detector, was suggested by several authors. The goal of these countermeasures is to divert missiles from their interception course. We quantitatively examined several suggested CM applications of femtosecond lasers from the literature. Our analyses show that application of femtosecond laser beams for dazzling of missile seeker heads is not in any way promising, neither via white-light generation in the ultra-short laser pulses nor via glowing plasma. In both these cases the generated light intensity is too low to successfully compete with the signal of a typical target. Taking into account literature reports, we conclude that the most promising application of femtosecond laser beams in the field of countermeasure applications seems to be related to inducing damage of the optical components of the seeker system.