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Missile Approach WarningThe Infrared vs Ultraviolet Debate
Geoff van Hees
10 March 2014
EW Asia 2014, The Prince Hotel, Kuala Lumpur
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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
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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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