Electro-Optical Systems The almost last lecture of Weapons Class

What are we talking about? Optically guided weapons Night vision goggles Thermal Imaging Laser Guided Munitions

Learning Objectives The student will understand the properties of Infrared radiation. The student will understand detector features and their effect on performance.

Electro-Optical Spectrum Electro-Optical Band Hz Visible ~10 15 Hz Infrared ~ 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) 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).

Lasers 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

Questions?