1. Electro-optic electronic countermeasures (ECM) and electronic protection measures (EPM) are required to deal with threats in the Electro-optic Spectrum; this includes the Visual and IR wavebands and the threat from Laser based systems.
2. Within the Electro-optic Spectrum, the Near IR, Visual and Near UV wavelengths from 3m to below 0.4m are considered.
3. This lesson will be dealt with in two halves:
a. Part 1: The Visual and IR threat.
b. Part 2: The Laser Systems threat.
OBJECTIVE
4. The aim of this lesson is to describe the techniques and defensive measures that will prevent the enemy from exploiting the Electro-optic Spectrum.
THE VISUAL AND IR THREAT
5. The sources of IR and UV energy have been discussed in previous lessons. All matter emits IR energy; the rate of emission and frequency is subject to Plank's Law. The main source of UV energy is from the Sun; there are very few other natural sources. The range of detection of UV wavelengths is significantly less, in comparable conditions, than the range at which IR wavelengths will be received because of attenuation in the atmosphere.
6. The source of IR and UV energy that is considered as a threat is mainly associated with missiles. UV energy is generated in the launch and boost phase of flight; IR energy is generated by the missile propulsion system (shorter wavelengths) and from the missile body (natural and kinetic heating- longer wavelengths).
7. The main threat to surface vessels today is the Anti-Ship Missile. Missile flight profiles vary from high flying cruise phases with a steep terminal dive, to the sea skimming missile. The missiles can be active or passive, with a mixture of active and/or passive sensors. TV and IR sensors are being used to complement Active Radar in the terminal phase to help to discriminate against decoys. Any means of reducing the ship signature, whether visual, noise, IR or RCS based, can only serve to make the platform a smaller and therefore a more elusive target.
8. The main threat to aircraft is, once again, the missile. Today's high-tech generation of passive air-to-air missiles, IRIS-T, AIM-9X, AA11 and Python 5 almost claim immunity against the full range of countermeasures. Shoulder launched missiles, available in huge numbers around the world, have forced combat aircraft to operate at altitudes above 15,000 feet. Radar guided missiles are capable of engaging targets above 70,000 feet. Integrated defensive aids suites in aircraft consist of Radar Warning Receivers (RWR), Missile Launch Warners (MLW), Missile Approach Warners (MAWS) which utilise sensors to detect an active radar or UV/IR sources. These systems can react automatically, dispersing chaff or flares, if a threat is detected. Because of the 'no escape zone' and decoy discrimination capabilities of modern generation missiles, laser based defensive systems are in use in helicopters, transport and commercial aircraft and under development for fighter aircraft.
9. On the ground, one of the most recent threat innovations in the past decade has been the use of laser guided weapons, laser designators and range finders and anti-personnel laser weapons. Personal protection measures are available against the latter and laser warning systems are now fitted to armoured vehicles to indicate the targeting process.
10. Initial detection, with the advent of satellite and UAV surveillance platforms, is of concern; the use of IR Imaging systems, high resolution optics and synthetic aperture radar (SAR) together with real time, high data and communication exchange systems makes concealment more difficult.
COUNTERMEASURES
11. The measures taken to prevent a platform from being detected begin in the conceptual stage of design. Modelling computers for both ships and aircraft ensure that the radar cross section, IR and EM signatures are optimised before build begins.
12. Contrast reduction measures, in the form of IR Paint or Camouflage, can be taken to ensure that the platform blends in with the background as deception measure. IR Paint is used to absorb the tell-tail wavelengths and re-emit them at a different frequency which is more easily attenuated. Camouflage is conventionally considered to defeat visual detection however, Low Light/Visibility and IR systems can also be camouflaged against threats
13. The colour and pattern of camouflage is important to defeat Low Light and IR systems. In the 1991 Gulf War, American forces using desert camouflage, coloured not to contrast with the background and of a material that emitted the natural IR wavelengths, was effective concealment. The Iraqi forces used camouflage that emitted a distinctive IR wavelength which contrasted to the background and made their positions more easily detectable.
14. The use of Decoy Flares to seduce the missile seeker is considered in depth Radiation Shielding is generally used to suppress an IR signature or to reduce a ship's RCS. In addition to IR Paint, IR Screens are used to simply block EO wavelengths. The IR signature from a ship's exhaust plume can be reduced by mixing cold air with the gas turbine engine exhaust before it is vented to the atmosphere through the funnel. Different engine options have been considered; diesel engine exhausts can be discharged underwater (diesels are however noisier and do not have a surge speed capability); electric motors and hybrid systems are under evaluation. The speed at which an engine is run also generates a larger IR signature as hot spots in the hull (engine, gearbox and exhaust locations) and in the exhaust plume.
15. Similar concerns apply to aircraft. The type of engine, use of afterburners (Plank's Law) and whether operating at supersonic or sub-sonic speeds also affect the IR signature in both the amount of energy that is emitted and the frequency at which it is emitted.
16. In another lesson however, the importance of the timely deployment and rate of expenditure of the stock of flares has tactical considerations.
17. Tactically, avoiding detection may be the priority that determines the routing of a mission and the manoeuvring around known threat locations. However it must be remembered that shoulder launched IR SAMs may be anywhere in the area. Low level flying and the use of terrain masking will also make detection more difficult, or if you have air superiority you may wish to fly at medium level above IR missiles MEZ.
18. First generation IR missiles were only successful when fired directly from behind the target; they were stern aspect only missiles. More modern missiles will detect an IR signature from a number of sources on the airframe, not just the exhaust plume.
19. IR energy is attenuated by water vapour and carbon dioxide. Warships can take advantage of these characteristics by hiding within a self-generated moisture or smoke screen. Most warships have a pre-wet system, originally installed to wash away nuclear, biological and chemical agents, that would be effective in reducing the ship IR signature.
20. In addition to expendable decoys such as flares, IR Jammers are available. These operate on the same principle as a radar noise jammer and are mainly fitted to armoured vehicles, transport aircraft and helicopters.
THE LASER THREAT
21. Lasers are being used more frequently on the battlefield as laser range finders and target designators. There is a significant and growing use of lasers as intentional or unintentional dazzle weapons against personnel. Systems are available for use on the battlefield and against aircrew piloting aircraft.
22. The range of injuries that can be sustained range from Glare, a flash blindness where permanent damage is done to the eye, to Retinal damage which can be permanent or Corneal damage which is usually temporary.
23. Eyes and skin are very sensitive to the shorter wavelengths of the Near IR and Visible waveband. The eye need protection in the bandwidth from 0.4m to 0.75m (here the light is visible) and 0.75m to 1.4m (source in near IR band is invisible to the eye). An Ng:YAG Laser operating at 1.06m is dangerous. Pulsed lasers are also more dangerous than CW lasers because of the power that can be discharged. Lasers are classed by using a measure known as the Normal Ocular Hazard Distance (NOHD). This is defined as the minimum distance at which that strength of laser will do no damage. Every individual has a natural aversion instinct; this gives a person a degree of protection against the weakest classes of laser, by quickly turning away, but will not protect against stronger classes of laser.
24. Protection can be achieved by fitting protective eyewear such as laser glasses that block the light by attenuation. Indirect viewing methods should also be employed. The STINGRAY battlefield laser locates an enemy optical system using a low power system and, when the location process is complete, fires a high energy laser into the enemy optical system.
25. Laser goggle protection in the Visible bandwidth requires a discolouring filter that makes target identification difficult. Protection technology ranges from Passive - absorbs or reflects the laser light, or Active - self actuating filter or external blanking. The ideal solution would be a protective system which would stop harmful energy from reaching the eye, block energy over a narrow bandwidth, work by day or night and be cheap. Current shortcomings are that protective goggles cannot protect against frequency agile laser weapons and cannot offer unrestricted viewing.
ELECTRO-OPTIC (EO) ECM AND EPM
26. Helmet visors are being developed that overcome some of these limitations by using 'Rugate Filter' technology. This filters out all light but the primary eye colours; transmission of light is reduced but proper perception of all colours allows for the mission to be accomplished.
27. Laser light can also be reflected by applying multi-layer thin dielectric film on a curved visor; transmission can be reduced by as much as 99%.
28. Blanking technology completely blanks out all radiation energy, once a warning is provided by the LWR.
29. The use of Smoke makes a target more difficult to acquire and, depending upon the wavelength of the laser, can diffuse and absorb the laser energy. Takes time to establish and effectiveness is dependent on the prevailing wind strength.
SUMMARY
30. Protection is based on preventing light reaching the eye; the more that is cut out, the less can be seen. It is not possible to cover all wavelength without increasing the limitations. Systems must be compatible with HUD, NVG and NBC. NVGs protect against Lasers but would be damaged themselves.
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