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Electro-Optical SystemsElectro-Optical Systems
The almost last lecture of Weapons Class
What are we talking about?What are we talking about?
• Optically guided weapons• Night vision goggles• Thermal Imaging• Laser Guided Munitions
Learning ObjectivesLearning Objectives
• The student will understand the properties of Infrared radiation.
• The student will understand detector features and their effect on performance.
Electro-Optical SpectrumElectro-Optical Spectrum
• Electro-Optical Band 1011-1016 Hz• Visible ~1015 Hz• Infrared ~1011-1014
Hz
• Portion of the EM spectrum that lies between X-rays and microwaves
Sources of EO Radiation
• Turbojet exhaust, a tank engine, or a person
• Lasers may serve as illuminator for an IR weapon’s guidance
• Man-made artificial illumination (lights, flares, etc)
• Natural sources
Sources (Radiators)Sources (Radiators)• Selective Emitters
– Narrow wavelength band – line spectra– Excitation of individual atoms or
molecules• Thermal
– Continuous spectrum of wavelengths with some max radiated energy at some particular λ
– Radiates in proportion to the absolute temperature (Kelvin).
LasersLasers
• Laser is light – a form of EM radiation
• Light Amplification by Stimulated Emission of Radiation
• Can emit in the ultraviolet, visible, and infrared portions of the spectrum
Lasers – Military Applications• Targeting tool
– Absorbed by target – thermal radiator– Reflected by target – selective radiator
• Modulated– Different lasers of the same frequency to be
deconflicted and limits enemy interference
• Weapon Systems: Hellfire, Maverick, Rockeye
• Stand alone: Laser Range finders, Beam riders, and laser target designators (LTD)
Infrared
• Can not be detected with the human eye
• Passive system that collects thermal radiation emitted from the target.
• Used in military and law enforcement applications.
IR image of a snake eating a mouse
Characteristics of Thermal Energy
• Attenuation – propagation losses primarily through:– Uneven spreading– Absorption– Scattering– Turbulence
• Refractive index fluctuations (Temp, pressure, density)
Detectors
• Photon – Convert absorbed photon energy into
released electrons
• Themal– Absorb energy over a broad band of
wavelengths– Causes tempurature of material to
increase• At least one inherent electrical property
that changes with temperature
Military Uses
• Laser guided munitions– Designated from air or ground
• Thermal homing missiles• Optical Guidance• Night Vision
Night Vision Devices (NVD)
• Low light level image intensifiers• Improve night vision
– Increase amount of light reaching the eye
– Light amplification• NVIS• FLIR
Night Vision Scopes
• “Amplify” existing light• Available light (photons) is
collected and focused on the image intensifier
• Conversion of photon to electron• CAN NOT see in complete dark
– IR illuminator
Image intensifier tube
Converts photons to electrons and back again
Thermal Imaging
LGB
TOW
TOW
Questions?