Night Vision-Abhisek Bilas

8/3/2019 Night Vision-Abhisek Bilas

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ABHISEK BILAS

REDG. No : 0501212646


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INTRODUCTION

Night Vision Technology enables us to see objects clearly inlevels of light approaching total darkness in the absence of anyartificial light.

Night vision technology refers to the quality of the imageintensifier tube housed by the night vision device (NVD).

The total landscape viewed through a modern night visionsystem appear almost illuminated while the same objectsviewed with a naked eye would appear only as indistinct

shadow.

Depending upon the way it is implemented it is broadlyclassified into two types

(i) Biological Night vision

(ii) Technical Night vision


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Enhanced spectral range

Enhanced spectral range techniques make the viewersensitive to types of light that would be invisible to ahuman observer.

Human vision is confined to a small portion of theelectromagnetic spectrum called visible range.

Enhanced spectral range allows the viewer to take

advantage of non-visible sources of electromagneticradiation (such as near-infrared or UV radiation)


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Enhanced intensity range

Enhanced intensity range is simply the ability to see with verysmall quantities of light. Although the human visual systemcan, in theory,detect single photons under ideal conditions.

Some animals have evolved better night vision through the useof a larger optical aperture, improved retina composition that

can detect weaker light over a larger spectral range, morephoto efficient optics in the eye, and improved neurologicalability.

Enhanced intensity range is achieved via technological meansthrough the use of an image intensifier,gain multiplication or

other very low-noise and high-sensitivity array ofphotodetectors.


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Biological night vision

In biological night vision, molecules of rhodopsin in the rods ofthe eye undergo a change in shape as light is absorbed bythem.

Rhodopsin in the human rods is insensitive to the longer red

wavelengths of light,so many people use red light to preservenight vision as it will not deplete the eye's rhodopsin stores inthe rods and instead is viewed by the cones.

Some animals,such as cats, dogs, and deer,have a structure

called the tapetum in the back of the eye that reflects light foreven better night vision than humans,in which only 10% of thelight that enters the eye falls on photosensitive parts of theretina.


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TECHNICAL NIGHTVISION

It is based upon theprinciples of photo electriceffect.

E = hf

E = W + KE

Where E=Energy of theradiation.

W=Work function.

KE=Kinetic energy of theelectrons.

h=Plancks constant.

f=Frequency of theradiation.

BASIC PRINCIPLE

PHOTOELECTRIC EFFECT

EMMISION OF ELECTRON FROM PHOTO CATHODE WHEN PHOTON

STRIKES ON THE SURFACE


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NIGHT VISION DEVICES

Night vision device (NVD) is an optical instrument thatallows images to be produced in levels of light

approaching total darkness.

The term usually refers to a complete unit, includingan image intensifier tube, a protective and generally

water-resistant housing, and some type of mounting

system.

Night vision device can work in two very differentways,depending on technology,

Image Enhancement Technique.

Thermal Imaging Technique.


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IMAGE ENHANCEMENTTECHNIQUE

Image-enhancement technology is the most importantaspect of night vision technique.

NVDs rely on a special tube, called an image-

intensifier tube, to collect and amplify infrared andvisible light.

It works by collecting the tiny amounts of light,including the lower portion of the infrared light

spectrum, that are imperceptible to our eyes, andamplify it to the point so that we can easily observethe image.


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Continues

Its working as follows..1.A conventional lens, called the objective lens, captures

ambient light and some near-infrared light.

2.The gathered light is sent to the image-intensifier tube. Inmost NVDs, the power supply for the image-intensifiertube receives power from two N-Cell batteries. The tubeoutputs a high voltage, about 5,000 volts, to the image-tube component

3.The image-intensifier tube has a photocathode, which isused to convert the photons of light energy into electrons.


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4.As the electrons pass through the tube, similar electrons

are released from atoms in the tube, multiplying the

original number of electrons by a factor of thousands

through the use of a micro channel plate (MCP) in thetube.MCP acts as electron multiplier.

5. At the end of the image-intensifier tube, the electrons hit a

screen coated with phosphors. The energy of theelectrons causes the phosphors to reach an excited state

and release photons.

6. The green phosphor image is viewed through anotherlens, called the ocular lens, which allows you to magnify

and focus the image. The NVD may be connected to an

electronic display, such as a monitor, or the image may

be viewed directly through the ocular lens.


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THERMAL IMAGING

Properties of thermal device:

Most thermal-imaging devices scan at a rate of 30

times per second.

They can sense temperatures ranging from -4 degrees

Fahrenheit (-20 degrees Celsius) to 3,600 F (2,000 C).

It can normally detect changes in temperature of

about 0.4F(0.2).


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TYPES OF THERMAL IMAGING

Un-cooled: The infrared-detector elements arecontained in a unit that operates at room temperature.This type of system is completely quiet, activatesimmediately and has the battery built right in.

Cryogenically cooled: These systems have theelements sealed inside a container that cools them tobelow 32 F (zero C). It has incredible resolution andsensitivity that result from cooling the elements.Cryogenically-cooled systems can "see" a differenceas small as 0.2 F (0.1 C) from more than 1,000 ft (300m) away.


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Continues..

Its working as follows1. A special lens focuses the infrared light emitted by

all of the objects in view.

2. The focused light is scanned by infrared-detectorelements. The detector elements create a verydetailed temperature pattern called a thermogram.

3. The thermogram created by the detector elements is

translated into electric impulses.

4. The impulses are sent to a signal-processing unit, acircuit board with a dedicated chip that translates theinformation from the elements into data for the

display.


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5. The signal-processing unit sends the information to

the display, where it appears as various colors

depending on the intensity of the infrared emission.

The combination of all the impulses from all of theelements creates the image.


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DIFFERENT GENERATIONSOF NVD

GENERATION 0 :

1. These NVDsuseactive infrared devices, using a large infraredlight source to illuminate targets.

2. A projection unit, called an IR Illuminator, is attached to the NVD.The unit projects a beam of near-infrared light.

3. Their image intensifier tubes function using an anode and an S-1photocathode, made primarily of silver, caesium, and oxygen toaccelerate the electrons.

4. Generation 0 devices took a lot of power to use, for both the tubeand the IR illuminator.

5. Had a very distorted picture due to a cone-shaped electrodedesign, and a short tube life due to the high electrical voltage.


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GENERATION1 :

1. These NVDs use ambient light provided by the moon and

stars in the environment so also called Starlight scopes.

2. They are much more power efficient, amplify light better,

and produced a superior image.

3. Generation-1 NVDs use the same image-intensifier tube

technology as Generation 0, with both cathode and anode.

4. These devices do not work very well on cloudy or

moonless nights.

5. Image distortion and short tube life are still a problem.


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GENERATION 2:

1. Major improvements was in image-intensifier tubes.

2. Increased sensitivity is due to the addition of the

microchannel plate to the image-intensifier tube.

3. MCP actually increases the number of electrons

instead of just accelerating the original electrons.

4. Light amplification was around 20000x

5. The images are significantly less distorted and

brighter than earlier-generation NVDs.


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GENERATION 3 :

1. It is essentially generation 2 technology with a

new photocathode material gallium arsenide and abetter MCP.

2. Gallium arsenide provides far better response to

near-infrared light and is very efficient atconverting photons to electrons.

3. the MCP is coated with an ion barrier film forincreased tube life

4. The light amplification is also improved, to around30000-50000x.


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GENERATION 4:

It significant overall improvement in both low andhigh level light environments.

The ion barrier is removed from the MCP that reduces

the background noise and enhances signal to noiseratio.

Automatic gated power supply system regulates the

photocathode voltage allowing the NVD toinstantaneously adapt to changing light conditions.

Images are significantly less distorted and brighter.


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VIEW THROUGH NVD

Through the use of NVD we can have a detailed view of the

landscape.

1. It is quite easy to see everything during the

day...

2. ...but at night, you can see very little.

3. View through Night vision devices.


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CONCLUSION

Night vision is one of the

emerging technology which is

used in different fields like in

industry, by the military persons.

So more sophisticated

technology needs to be

developed to get undistorted

images with high resolution.


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Night Vision-Abhisek Bilas

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