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 Warning Sensor? 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. Two classes of passive detectors • • PAGE 2 Ultraviolet Infrared . typically from the missile motor plume. Passive/Optical detection – relies on the signals emitted from the threat. Number of Line Replaceable units.Requirements for Optical Missile Detection Field of view • • Cover 360° in azimuth. Dwell time • • PAGE 3 The higher the scan rate the shorter the dwell time Need staring arrays. Min 90° (preferably 180°) in elevation. LRUs • 4 to 6 sensors for spherical coverage. Frame rate • Frame rate of at least 10ms. . condensation and icing should not significantly affect the operation of the sensors. .Requirements for Optical Missile Detection Distance Estimation • • Needed for optimal counter-measure deployment. fog. at best. Passive systems provide an estimate of distance and time to impact. All-weather operation • PAGE 4 Rain. IR vs UV Wavelength Choice IR – Two traditional Wavelengths • • • 3-5µ Band • CO2 absorption limits useful bandwidth. Low false alarm rate from background radiation. 8-12µ Band • • Number of problems. . Circumvents limiting factors of IR. High false alarm rate. UV – Solar blind • • • PAGE 5 Technical challenge to create. Wavelength related pixel size requires large detector arrays and optics of impractically large size. Possible with significant amounts of processing and tracking.IR vs UV Pixel Resolution IR – Needs High Resolution detector • • • Cluttered background – Surface to Air scenario. Source below the ozone layer can be detected using a low resolution detector. . Clutter rejection is a major issue. UV – Low resolution detector sufficient • • PAGE 6 Solar Blind system – no background radiation or reflections. increases exponentially in day light due to solar illumination. IR vs UV Detection and Tracking IR – Can track missile after motor burn-out • • Possible for air to air. Dense. . UV – Rocket motor must be burning • PAGE 7 Track initiated as soon as any energy is detected. background radiation. low-altitude atmosphere. Surface to air – Low seeker head heat. IR vs UV Spectral Discrimination IR – Two/Multi-Colour detection • • • Needed to assist with suppression of background clutter. . revert back to highresolution with its attendant technical challenges UV – Single-colour detection • PAGE 8 Few sources hot enough to radiate significant amounts of short-wavelength – does include the threat to be detected. Measuring in two colours doubles the pixel count needed. Target smaller that 1 pixel. wide-angle optics mounted outside of an aircraft in an operational environment. Not necessary for high resolution across the FOV. Difficult to protect exposed large-aperture. IR optical materials are expensive and fragile. UV – Extremely robust • • • PAGE 9 Optics made mostly from fused silica (quartz). Low resolution – simple manufacturing process. .IR vs UV Optical Implications IR – Physically large detectors to accommodate required pixel array • • • Low optical image – pixel image blurred – reduced sensitivity and scene resolution. Cooling – mechanical refrigeration or thermo-electrical. Uncooled – less sensitive. . UV. complexity and life-cycle costs. Increases power consumption. Decreases system reliability. Thermal noise does not approach the high energy of the UV photons that are detected.Uncooled • • PAGE 10 No cooling needed.IR vs UV Cooling IR – Cooled • • • • • Need to reduce detector noise. weight. bit depth and single colour spectral resolution.4 trillion bits per second – Not currently practical for a cost-effective airborne or mobile application. . Readout of four 2-colour 16000 x 16000 pixel detectors at 100Hz and 12 bits per pixel – 2.IR vs UV Data Rates IR – WOW! • • Assumption – Large area IR detector that can read out the required frame rate and the resultant data rates can be computed. Lower spatial resolution. UV – No WOW factor • • PAGE 11 Effective data rate of a UV system is at least 5 orders of magnitude lower than an IR system. .IR vs UV Comparison IR Band • • • • Physical constraints – You can’t argue with physics. All weather capability – not affected by water or moisture in the atmosphere. Significantly cheaper and more durable. High cost and complexity vs reduced reliability and performance. Solar radiation saturates and blinds sensors– impacts POW. All weather operation not practical. UV Band • • • PAGE 12 Solar blind phenomenon removes need for high detector resolution and large dynamic range. PAGE 13 . it is not suitable as a missile warning application against surface launched missiles in the real world. 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. all-weather scenario.Conclusion IR technology delivers excellent results when its strengths are correctly exploited.
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