 Ability to see in a dark environment  Night vision is made possible by the combination of two approaches : Sufficient spectral range Sufficient intensity range

 Spectral Range - Human vision is confined to visible light portion of spectrum.  Enhanced spectral range allows the viewer to take advantage of non-visible portion of spectrum.  Intensity Range - Sufficient intensity range is the ability to see with very small quantity of light.  Enhanced intensity range can be achieved by the use of an image intensifier and an array of photodetectors.

BIOLOGICAL NIGHT VISION  Rhodopsin – the chemical that allows night vision and extremely sensitive to light.  Rhodopsin in human rods are less sensitive to red light.  Many animals have a tissue layer called the tapetum lucidum.  Nocturnal mammals have Inverted rods, consists of heterochromatin and euchromatin.  Large size of eye and large size of pupil relative to eye contribute to night vision.

Night glasses are telescopes or binoculars with a large diameter objective. Large lenses can gather light and concentrate light. To overcome the limited dilation of human pupil, soldiers use atropine eye drops. Major drawback – they have large size and weight.

 Active infrared night vision combines infrared illumination of spectral range nm.  The resulting scene appears as a monochrome image on a normal display device.  Because these systems can incorporate illuminators that produce high levels of infrared light.  The resulting images are typically higher resolution than other night vision technologies.  It is now commonly found in security applications because of effective night time imaging under low light conditions.

Thermal imaging cameras are excellent tools for night vision. They detect thermal radiation and do not need a source of illumination. They produce an image in the darkest of nights and can see through light fog, rain and smoke. Thermal imaging cameras make small temperature differences visible.

It is a vacuum tube based device Converts visible light from an image This is much like CRT Television Instead of color guns the photocathode does the emitting. Image is intensified, because output visible light is brighter than the incoming IR light. Most popular image intensifier is drop-in ANVIS module.

INFRARED LIGHT  Near-infrared (near-IR) - Closest to visible light, range from 0.7 to 1.3 microns, or 700 billionths to 1,300 billionths of a meter.  Mid-infrared (mid-IR) - ranges from 1.3 to 3 microns. Both near-IR and mid-IR are used by remote controls.  Thermal-infrared (thermal-IR) - Occupying the largest part of the infrared spectrum. Wavelengths ranging from 3 microns to over 30 microns.

GENERATIONS Generation 0 : created original night vision system IR Illuminator attached to NVD Major Problem- Quickly duplicated by hostile nations in Military use Generation 1 : Use of Passive infrared instead of active They use ambient light from moon and stars No need of source of projected infrared Problem – image distortion and short tube life

Generation 2 :  improved resolution and performance  Ability to see in extremely low light  Sensitivity increased due to addition of microchannel plates  Less distorted and brighter Generation 3 :  Better resolution and sensitivity  Photocathode made using Gallium Arsenide, efficient in converting photons to electrons  MCP is coated with ion barrier increase the life of tube

Generation 4 :  Removal of ion barrier from MCP reduces background noise and enhances S/N ratio  Images are less distorted and brighter  Addition of an automatic gated power supply enables NVD to respond to fluctuations in lighting conditions  NVD can benefit from use of an IR Illuminator in very dark areas  Tubes that meet military requirements – MILSPEC  Tubes that fail to meet military requirements - COMSPEC

ATOM  States of excitation : Ground state and Excited State  Atom has a nucleus and an electron cloud.  Transition of electron from excited state to ground state release energy called photon  Emitted photon has a very specific wavelength(color)

 A special lens - focuses the infrared light emitted by all of the objects in view.  Infrared Detector - detector elements create a very detailed temperature pattern called a thermogram.  Created thermogram is translated into electric impulses.  Impulses are sent to a signal- processing unit  It translates the information from the elements into data for the display.  Signal-processing unit sends the information to the display.

 Two types of thermal imaging devices :  Un-cooled : o Most common type. o The infrared-detector elements operates at room temperature. o System is completely quiet, activates immediately and has the battery built right in.  Cryogenically cooled : o More expensive and more susceptible to damage from rugged use. o Systems have the elements sealed inside a container that cools them to below 32 F (zero C). o Incredible resolution and sensitivity.

o Objective lens : captures ambient light and some near-infrared light. o It is sent to the image- intensifier tube. o Photocathode : Used to convert the photons into electrons. o Microchannel plate (MCP): It multiplies the original number of released electrons by a factor of thousands. o It works as an electron multiplier.

 When electrons from the photo cathode hit the first electrode of the MCP, they are accelerated into the glass microchannels.  Microchannels cause thousands of other electrons to be released in each channel using a process - cascaded secondary emission.  A chain reaction results in thousands of electrons leaving the channel.

At the end of the image- intensifier tube, electrons hit a phosphor coated screen. Energy of the electrons causes the phosphors to reach an excited state and release photons. The green phosphor image is viewed through another lens, called the ocular lens.

Night-vision equipment can be split into three broad categories :  Scopes  Goggles  Cameras

Scopes :  Normally handheld or mounted on a weapon.  They are monocular (one eye-piece).  They are good to get a better look at a specific object.

Goggles :  Most often they are worn on head.  Goggles are binocular (two eye-pieces).  They have a single lens or stereo lens, depending on the model.  They are excellent for constant viewing, such as moving around in a dark building.

Cameras : Cameras with night-vision technology can send the image to a monitor for display or to a VCR for recording Used in buildings and helicopters Many of the newer camcorders have night vision built right in.

APPLICATIONS Military Law enforcement Hunting Wildlife Observation Surveillance Security Navigation Hidden object Detection Entertainment

CONCLUSION  Original purpose was to locate enemy targets at night  Detectives and private investigators use this to trace people  Many businesses have permanently-mounted cameras equipped with night vision to monitor surroundings  It has many advantages in commercial and military purposes