Missile Approach WarningThe Infrared vs Ultraviolet Debate

Geoff van Hees

10 March 2014

EW Asia 2014, The Prince Hotel, Kuala Lumpur

What is a Missile Approach WarningSensor?

Purpose: To detect IR-guided missiles that pose

a threat to the platform

Two approaches

Active detection uses RF energy to illuminate environment and detect incoming threats.

Passive/Optical detection relies on the signals emitted from the threat, typically from the missile motor

plume.

Two classes of passive detectors

Ultraviolet Infrared

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Requirements for Optical MissileDetection

Field of view

Cover 360 in azimuth. Min 90 (preferably 180) in elevation.

Number of Line Replaceable units, LRUs

4 to 6 sensors for spherical coverage.

Frame rate

Frame rate of at least 10ms.

Dwell time

The higher the scan rate the shorter the dwell time Need staring arrays.

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Requirements for Optical MissileDetection

Distance Estimation

Needed for optimal counter-measure deployment. Passive systems provide an estimate of distance and

time to impact, at best.

All-weather operation

Rain, fog, condensation and icing should not significantly affect the operation of the sensors.

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IR vs UVWavelength Choice

IR Two traditional Wavelengths

3-5 Band CO2 absorption limits useful bandwidth.

8-12 Band Number of problems. Wavelength related pixel size requires large detector

arrays and optics of impractically large size.

High false alarm rate.

UV Solar blind

Technical challenge to create. Circumvents limiting factors of IR. Low false alarm rate from background radiation.

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IR vs UVPixel Resolution

IR Needs High Resolution detector

Cluttered background Surface to Air scenario. Clutter rejection is a major issue, increases

exponentially in day light due to solar illumination.

Possible with significant amounts of processing and tracking.

UV Low resolution detector sufficient

Solar Blind system no background radiation or reflections.

Source below the ozone layer can be detected using a low resolution detector.

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IR vs UVDetection and Tracking

IR Can track missile after motor burn-out

Possible for air to air. Surface to air Low seeker head heat, background

radiation. Dense, low-altitude atmosphere.

UV Rocket motor must be burning

Track initiated as soon as any energy is detected.

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IR vs UVSpectral Discrimination

IR Two/Multi-Colour detection

Needed to assist with suppression of background clutter.

Measuring in two colours doubles the pixel count needed.

Target smaller that 1 pixel, revert back to high-resolution with its attendant technical challenges

UV Single-colour detection

Few sources hot enough to radiate significant amounts of short-wavelength does include the threat to be

detected.

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IR vs UVOptical Implications

IR Physically large detectors to accommodate

required pixel array

Low optical image pixel image blurred reduced sensitivity and scene resolution.

IR optical materials are expensive and fragile. Difficult to protect exposed large-aperture, wide-angle

optics mounted outside of an aircraft in an operational

environment.

UV Extremely robust

Optics made mostly from fused silica (quartz). Low resolution simple manufacturing process. Not necessary for high resolution across the FOV.

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IR vs UVCooling

IR Cooled

Need to reduce detector noise. Uncooled less sensitive. Cooling mechanical refrigeration or thermo-electrical. Increases power consumption, weight, complexity and

life-cycle costs.

Decreases system reliability.

UV- Uncooled

No cooling needed. Thermal noise does not approach the high energy of

the UV photons that are detected.

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IR vs UVData Rates

IR WOW!

Assumption Large area IR detector that can read out the required frame rate and the resultant data rates can

be computed.

Readout of four 2-colour 16000 x 16000 pixel detectors at 100Hz and 12 bits per pixel 2.4 trillion bits per

second Not currently practical for a cost-effective

airborne or mobile application.

UV No WOW factor

Effective data rate of a UV system is at least 5 orders of magnitude lower than an IR system.

Lower spatial resolution, bit depth and single colourspectral resolution.

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IR vs UVComparison

IR Band

Physical constraints You cant argue with physics. All weather operation not practical. Solar radiation saturates and blinds sensors impacts

POW.

High cost and complexity vs reduced reliability and performance.

UV Band

Solar blind phenomenon removes need for high detector resolution and large dynamic range.

All weather capability not affected by water or moisture in the atmosphere.

Significantly cheaper and more durable.PAGE 12

Conclusion

IR technology delivers excellent results when its

strengths are correctly exploited, it is not suitable

as a missile warning application against surface

launched missiles in the real world, all-weather

scenario.

Has advantages over UV in the air to air

scenario based on ability for longer detection

range and ability to track a missile after the

motor has burnt out.

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