Night Vision

Night vision is the ability to see in a dark environment. Whether by biological or technological means, night vision is made possible by a combination of two approaches: sufficient spectral range, and sufficient intensity range. Humans have poor night vision compared to many animals, in part because the human eye lacks a tapetum lucidum.

                                                      

Two American Soldiers pictured during the  2003 Iraq War seen through an image intensifier

                                                                            

 

Types of ranges

NightSpectral

range-useful spectral range techniques can sense radiation that is invisible to a human observer. Human vision is confined to a small portion of the electromagnetic spectrum called visible light. Enhanced spectral range allows the viewer to take advantage of non-visible sources of electromagnetic radiation (such as near-infrared or ultraviolet radiation). Some animals can see using much more of the infrared and/or ultraviolet spectrum than humans.

Intensity range

Sufficient intensity range is simply the ability to see with very small quantities of light. Although the human visual system can, in theory, detect single photons under ideal conditions, the neurological noise filters limit sensitivity to a few tens of photons, even in ideal conditions.^[2]

Many animals have better night vision than humans do, the result of one or more differences in the morphology and anatomy of their eyes. These include having a larger eyeball, a larger lens, a larger optical aperture (the pupils may expand to the physical limit of the eyelids), more rods than cones (or rods exclusively) in the retina, a tapetum lucidum.

Enhanced intensity range is achieved via technological means through the use of an image intensifier, gain multiplication CCD, or other very low-noise and high-sensitivity array of photodetectors.

Biological night vision

In biological night vision, molecules of rhodopsin in the rods of the eye undergo a change in shape as they absorb light. Rhodopsin is the chemical that allows night-vision, and is extremely sensitive to light. Exposed to a spectrum of light, the pigment immediately bleaches, and it takes about 30 minutes to regenerate fully, but most of the adaptation occurs within the first five or ten minutes in the dark. Rhodopsin in the human rods is less sensitive to the longer red wavelengths of light, so many people use red light to help preserve night vision as it only slowly depletes the eye's rhodopsin stores in the rods and instead is viewed by the cones.

Many animals have a tissue layer called the tapetum lucidum in the back of the eye that reflects light back through the retina, increasing the amount of light available for it to capture. This is found in many nocturnal animals and some deep sea animals, and is the cause of eyeshine. Humans lack a tapetum lucidum.

Nocturnal mammals have rods with unique properties that make enhanced night vision possible. The nuclear pattern of their rods changes shortly after birth to become inverted. In contrast to contemporary rods, inverted rods have heterochromatin in the center of their nuclei and euchromatin and other transcription factors along the border. In addition, the outer nuclear layer (ONL) in nocturnal mammals is thick due to the millions of rods present to process the lower light intensities of a few photons. Rather than being scattered, the light is passed to each nucleus individually.^[3] In fact, an animal's ability to see in low light levels may be similar to what humans see when using first- or perhaps second-generation image intensifiers.^{[citation needed]}

A larger size of pupil relative to the rest of the eye, also aids night vision.^{[citation needed]}

Night vision technologies

Night vision technologies can be broadly divided into three main categories:

Image intensification

Image intensification technologies work on the principle of magnifying the amount of received photons from various natural sources such as starlight or moonlight. Examples of such technologies include night glasses and low light cameras.

Active illumination

Active illumination technologies work on the principle of coupling imaging intensification technology with an active source of illumination in the near infrared (NIR) or shortwave infrared (SWIR) band. Examples of such technologies include low light cameras.

Thermal imaging

Thermal imaging technologies work by detecting the temperature difference between the background and the foreground objects.

Night glasses

Binoculars (night vision goggles on flight helmet) Note: the green color of the objective lenses is the reflection of the Light Interference Filters, not a glow.

Night glasses are telescopes or binoculars with a large diameter objective. Large lenses can gather and concentrate light, thus intensifying light with purely optical means and enabling the user to see better in the dark than with the naked eye alone. Often night glasses also have a fairly large exit pupil of 7 mm or more to let all gathered light into the user's eye. However, many people can't take advantage of this because of the limited dilation of the human pupil. To overcome this, soldiers were sometimes issued atropine eye drops to dilate pupils. Before the introduction of image intensifiers, night glasses were the only method of night vision, and thus were widely utilized, especially at sea. Second World War era night glasses usually had a lens diameter of 56 mm or more with magnification of seven or eight. Major drawbacks of night glasses are their large size and weight.

Active infrared

Imaging results with and without active-infrared.

Active infrared night vision combines infrared illumination of spectral range 0.7–1 μm (just below the visible spectrum of the human eye) with CCD cameras sensitive to this light. The resulting scene, which is apparently dark to a human observer, appears as a monochrome image on a normal display device.^[4]

Because active infrared night vision systems can incorporate illuminators that produce high levels of infrared light, the resulting images are typically higher resolution than other night vision technologies.^[5][6] Active infrared night vision is now commonly found in commercial, residential and government security applications, where it enables effective night time imaging under low light conditions. However, since active infrared light can be detected by night vision goggles, it is generally not used in tactical military operations.

Laser range gated imaging

Laser range gated imaging is another form of active night vision which utilizes a high powered pulsed light source for illumination and imaging. Range gating is a technique which controls the laser pulses in conjunction with the shutter speed of the camera's detectors.^[7] Gated imaging technology can be divided into single shot, where the detector captures the image from a single light pulse to multi-shot, where the detector integrates the light pulses from multiple shots to form an image.

One of the key advantages of this technique is the ability to perform target recognition as opposed to detection with thermal imaging.

Thermal vision

Thermal imaging cameras are excellent tools for night vision. They perceive 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. Thermal imaging cameras are widely used to complement new or existing security networks.

Image intensifier

The image intensifier is a vacuum-tube based device that converts visible light from an image so that a dimly lit scene can be viewed by a camera or the naked eye. While many believe the light is "amplified," it is not. When light strikes a charged photocathode plate, electrons are emitted through a vacuum tube that strike the microchannel plate that cause the image screen to illuminate with a picture in the same pattern as the light that strikes the photocathode, and is on a frequency that the human eye can see. This is much like a CRT television, but instead of color guns the photocathode does the emitting.

The image is said to become "intensified" because the output visible light is brighter than the incoming IR light, and this effect directly relates to the difference in passive and active night vision goggles. Currently, the most popular image intensifier is the drop-in ANVIS module, though many other models and sizes are available at the market.

Night vision devices

A night vision device (NVD) is a device comprising an image intensifier tube in a rigid casing, commonly used by military forces. Lately night vision technology has become more widely available for civilian use, for example, EVS, or enhanced vision systems, which are included in the latest avionics packages in cirrus and Cessna planes to help pilots with situational awareness and avoid accidents. eVS is also available for rotary wing operators.

A specific type of NVD, the night vision goggle (or NVG) is a night vision device with dual eyepieces; the device can utilize either one intensifier tube with the same image sent to both eyes, or a separate image intensifier tube for each eye. Night vision goggle combined with magnification lenses constitutes night vision binoculars. Other types include monocular night vision devices with only one eyepiece which may be mounted to firearms as night sights. NVG and EVS technologies are becoming standard operating products on helicopter operations to improve safety. The NTSB is considering EVS as recommended equipment for safety features.

Night Vision Report page 7 of 7

Future Scope

The Army is pushing night-vision technologies into the digital realm. Future night-vision goggles are being designed not just to see better at night but also to allow soldiers to share images of what they see with other soldiers who may be miles away.
Technologists agree that the goal is feasible, but contractors currently working on these next-generation goggles are encountering challenges in meeting the Army’s requirements for power, size and weight.
The technical difficulties may delay Army plans to award a production contract next year. 
Soldiers currently use image intensification. They also employ infrared thermal sensors, which sense temperature differences. Warmer items appear brighter on a display.
The fusion of both technologies would result in night-vision goggles that merge the strengths of image intensification — a clear, sharp green-tinted picture — with the advantages of infrared — the ability to see practically under any environmental condition. Green is the color that the human eye sees most easily.
The combination of the two systems into a single optical device resulted in what the Army calls an “enhanced night vision goggle,” or ENVG.
The current ENVG, however, is analog, and does not pipe data into the soldier’s radio, as the Army wanted.
The Army has awarded several contracts for the development of digital ENVGs. It plans to evaluate the designs in July to see how the technologies have matured from the previous test last year.
Soldiers will test the goggles in a variety of environments, including in urban training facilities and on woodland patrols.
The largest provider of night-vision technology to the military, Roanoke, Va.-based ITT Night Vision, manufactures the ENVG for the Army. Engineers there are developing a digital version.
For the digital ENVG, the company has replaced the standard image intensifier tube with a new digital sensor, the MicroChannel Plate Complimentary Metal-Oxide Semiconductor, or MCP-CMOS. The microchannel plate sits inside a vacuum package between the photocathode and the electron-collecting semiconductor array.
The Army believes that by 2014, the digital ENVG-D will be ready for production, says Kang.
The Army’s program executive officer for soldier equipment, Brig. Gen. Peter N. Fuller, says he is confident that contractors can overcome the technical difficulties. But he says he is not surprised by the troubles experienced by ENVG because the technology is such a huge leap from the current systems.
A request for proposals is expected this fall.
According to Fuller, the Army estimates that ENVGs will cost $18,000 apiece.   

References

1. Night Vision & Electronic Sensors Directorate - Fort Belvoir, Virginia
2. Night Vision by Ronald Munson
3. Electronics technology handbook by By Neil Sclater
4. Themal Night Vision Technology by John Eargle
5. http://en.wikipedia.org/wiki/Night_vision
6. http://en.wikipedia.org/wiki/Night_vision_device
7. http://electronics.howstuffworks.com/nightvision3.html
8. http://www.nightvision.com/military/militaryhome.html
9. http://www.physics.ohio-state.edu/~wilki...index.html
10. http://www.physics.ohio-state.edu/~wilki...index.html
11. http://www.atncorp.com/HowNightVisionWorks
12. http://www.morovision.com/hownightvisionworks.htm
13. http://www.alanaecology.com/acatalog/Introduction_to_ Nightvision.html
14. www.hownightvisionworks.com
15. http://www.morovision.com/hownightvisionworks.htm
16. http://www.photonis.com/nightvision/technology/image_intensifier_glossary
17. http://www.yachtingmagazine.com/article/Heated-Discussions
18. http://www.nationaldefensemagazine.org/archive/2009/October/Pages/FutureNightVisionDevicesMoreThanJustGoggles.aspx

Night Vision Report page 6 of 7

Applications

Common applications for night vision include:

• Military

• Law enforcement

• Hunting

• Wildlife observation

• Surveillance

• Security

• Navigation

• Hidden-object detection

• Entertainment

The original purpose of night vision was to locate

enemy targets at night. It is still used extensively by the military for that purpose, as well as for navigation, surveillance and targeting. Police and security often use both thermal-imaging and image-enhancement technology, particularly for surveillance. Hunters and nature enthusiasts use NVDs to maneuver through the woods at night. Detectives and private investigators use night vision to watch people they are assigned to track. Many businesses have permanently-mounted cameras equipped with night vision to monitor the surroundings. A really amazing ability of thermal imaging is that it reveals whether an area has been disturbed -- it can show that the ground has been dug up to bury something, even if there is no obvious sign to the naked eye. Law enforcement has used this to discover items that have been hidden by criminals, including money, drugs and bodies. Also, recent changes to areas such as walls can be seen using thermal imaging, which has provided important clues in several cases.

Advantages

· High sensitivity in low-light

· High speed imaging capability

· Able to detect people and vehicles at at great distances

· Eliminates shadows and reveal identifying lettering numbers and Objects

Disadvantages

— Near illumination is required

— U can get blind if u look at something bright

— Optical distortion-classic & manufacturing

— Night vision does not present normal depth perception.

— Black Spots

— Honeycomb

Conclusion

— Night vision technology was developed by the US defense department mainly for defense purposes

— Night Vision Technologies are now used in the daily lives.

— While thermal imaging is great for detecting people or working in near-absolute darkness, most night-vision equipment uses image-enhancement technology.

— Many people are beginning to discover the unique world that can be found after darkness falls

— One estimate shows an entire battalion could be outfitted with the ability to "own the night" for less than two million dollars

— In future many Other method will used for efficient way of working of Night Vision Technology

Night Vision report page 5 of 7

Characteristics of Night Vision

Using intensified night vision is different from using regular binoculars and/or your own

eyes. Below are some of the aspects of night vision that you should be aware of when you

are using an image intensified night vision system.

Textures, Light and Dark

Objects that appear light during the day but have a dull surface may appear darker,

through the night vision unit, than objects that are dark during the day but have a highly

reflective surface. For example, a shinny dark colored jacket may appear brighter than a

light colored jacket with a dull surface.

Depth Perception

Night vision does not present normal depth perception.

Fog and Rain

Night vision is very responsive to reflective ambient light; therefore, the light reflecting

off of fog or heavy rain causes much more light to go toward the night vision unit and

may degrade its performance.

Honeycomb

This is a faint hexagonal pattern which is the result of the manufacturing process.

Black Spots

A few black spots throughout the image area are also inherent characteristics of all night

vision technology. These spots will remain constant and should not increase in size or

number. See example below of an image with black spots.

Equipments

Night-vision equipment can be split into three broad categories:

Scopes - Normally handheld or mounted on a weapon, scopes are monocular (one eye-piece). Since scopes are handheld, not worn like goggles, they are good for when you want to get a better look at a specific object and then return to normal viewing conditions.

Goggles - While goggles can be handheld, they are most often worn on the head. Goggles are binocular (two eye-pieces) and may have a single lens or stereo lens, depending on the model. Goggles 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. When night-vision capability is desired in a permanent location, such as on a building or as part of the equipment in a helicopter, cameras are used. Many of the newer camcorders

have night vision built right in.

Night vision report page 4 of 7

Generation 2 - The micro channel plate (MCP) electron multiplier prompted Gen 2 development in the 1970s. The "gain" provided by the MCP eliminated the need for back-to-back tubes - thereby improving size and image quality. The MCP enabled development of hand held and helmet mounted goggles.

Second-generation image intensification significantly increased gain and resolution by employing a microchannel plate. Figure 2 depicts the basic configuration. The microchannel plate is composed of several million microscopic hollow glass channels fused into a disk. Each channel, approximately 0.0125 mm in diameter, is coated with a special semiconductor which easily liberates electrons. A single electron entering a channel initiates an avalanche process of secondary emission, under influence of an applied voltage, freeing hundreds of electrons. These electrons, effectively collimated by the channel, increase the resolution of the device. With additional electron optics, details as fine as 0.025 mm can be realized (half the diameter of a human hair).

Current image intensifiers incorporate their predecessor's resolution with additional light amplification. The multialkali photocathode is replaced with a gallium arsenide photocathode; this extends the wavelength sensitivity of the detector into the near infrared. The moon and stars provide light in these wavelengths, which boosts the effectively available light by approximately 30%, bringing the total gain of the system to

around 30,000.slightgreen tint similar to some sunglasses. The apparent lighting of the landscape on a darknight is comparable to what the unaided eye would see on a clear winter night with freshsnow on the ground and a full moon.

Generation 3 - Two major advancements characterized development of Gen 3 in the late 1970s and early 1980s: the gallium arsenide (GaAs) photocathode and the ion-barrier film on the MCP. The GaAs photocathode enabled detection of objects at greater distances under much darker conditions. The ion-barrier film increased the operational life of the tube from 2000 hours (Gen 2) to 10,000 (Gen 3), as demonstrated by actual testing and not extrapolation.

Generation 4 - for a good explanation of this commonly misunderstood advancement in night vision technology. When discussing night vision technology, you also may hear the term "Omnibus" or "OMNI". The U.S. Army procures night vision devices through multi-year/multi-product contracts referred to as "Omnibus" - abbreviated as "OMNI". For each successive OMNI

contract, ITT has provided Gen 3 devices with increasingly higher performance. ( See

range detection chart directly below) Therefore, Gen 3 devices may be further defined as

OMNI 3, 4, 5, etc. Current Omnibus contract as of 2006 is OMNI 7.

If you're using night vision to find a lost person in the woods, to locate boats or buoys on

the water, or to stargaze into the wilderness, you need Generation 3 because it creates the

best images when there is very little ambient light. Generation 2 may be the choice in

situations with higher levels of ambient light.

KEY GENERATION DEVELOPMENTS:

• GENERATION 1 (Developed in 1960's);

o Vacuum Tube Technology

o Full Moon Operation

o Amplification: 1,000

o Operating Life: 2,000 Hours

• GENERATION 2 (Developed in 1970's);

o First Micro channel Plate (MCP) Application

o One-Quarter Moon Operation

o Amplification: 20,000

o Operating Life: 2,500 Hours

• GENERATION 2+ (1970s)

o Development increased image tube bias voltage to improve gain.

o Additionally, a glass faceplate was added to improve resolution.

• GENERATION 3 (Developed in 1990's);

o Improved MCP & Photocathode

o Starlight Operation

o Amplification: 40,000

o Operating Life: 10,000 Hour

• GENERATION 4 Enhanced (2000's);

o Improvements in the photocathode and MCP resulted in increased gain

and resolution.

Night vision report page 3 of 7

There are two common types of thermal-imaging devices:

• Un-cooled - This is the most common type of thermal-imaging device. The infrared-detector elements are contained in a unit that operates at room temperature. This type of system is completely quiet, activates immediately and has the battery built right in.

• Cryogenically cooled - More expensive and more susceptible to damage from rugged use, these systems have the elements sealed inside a container that cools them to below 32 F (zero C). The advantage of such a system is the incredible resolution and sensitivity that result from cooling the elements. Cryogenically-cooled systems can "see" a difference as small as 0.2 F

(0.1 C) from more than 1,000 ft (300 m) away, which is enough to tell if a person is

holding a gun at that distance! While thermal imaging is great for detecting people or working in near-absolute

Generations

NVD Evolved from bulky optical instruments in lightweight goggles through the advancement of image intensification technology. Types of night vision Categorized by generations each substantial change NVT establishes a new generation Categorized into:

Generations	Invention Time	Uses
Generation 0	The earliest (1950's)	Created by US Army Uses active infrared.
Generation 1	1960's (Vietnam Era)	Uses passive infrared Uses ambient light provided by the moon and the stars.
Generation 2	late 1970s and early 1980s	Offer improved resolution and performance over Generation-1 devices.
Generation 3	1990	Uses the gallium arsenide (GaAs) photocathode and the ion-barrier Film on the MCP.
Generation 4	2000	Known as filmless and gated technology Shows significant improvement in both high- and low-level light environments.

Generation 0 - The earliest (1950's) night vision products were based on image conversion, rather than intensification. They required a source of invisible infrared (IR) light mounted on or near the device to illuminate the target area.

Generation 1 - The "starlight scopes" of the 1960's (Vietnam Era) have three image Intensifier tubes connected in a series. These systems are larger and heavier than Gen 2 and Gen 3. The Gen 1 image is clear at the center but may be distorted around the edges. (Low-cost Gen 1 imports are often mislabeled as a higher generation. Figure illustrates first-generation night vision. Incoming light is collimated by fiber optic plates before impacting a photocathode t which releases electrons, which in turn impact a phosphor screen. The excited screen emits green light into a second fiber optic plate, and the process is repeated. The complete process is repeated three times providing an overall gain of 10,000.

Night vision Report page 2 of 7

Types of Night Vision Technology

Image Enhancement

Image-enhancement technology is what most people think of when you talk about night

vision. In fact, image-enhancement systems are normally called night-vision devices

(NVDs). NVDs rely on a special tube, called an image-intensifier tube, to collect and

amplify infrared and visible light.

The image-intensifier tube changes photons to electrons and back again.

Here's how image enhancement works:

• A conventional lens, called the objective lens, captures ambient light and some near-infrared light.

• The gathered light is sent to the image-intensifier tube. In most NVDs, the power supply for the image-intensifier tube receives power from two N-Cell or two "AA" batteries. The tube outputs a high voltage, about 5,000 volts, to the image-tube components

.

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

• 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 microchannel plate (MCP) in the tube. An MCP is a tiny glass disc that has millions of microscopic holes (microchannels) in it, made using fiber-optic technology. The MCP is

contained in a vacuum and has metal electrodes on either side of the disc. Each channel is about 45 times longer than it is wide, and it works as an electron multiplier. When the electrons from the photo cathode hit the first electrode of the MCP,

they are accelerated into the glass microchannels by the 5,000-V bursts being sent between the electrode pair. As electrons pass through the microchannels, they cause thousands of other electrons to be released in each channel using a process called cascaded secondary emission. Basically, the original electrons collide with the side of the channel, exciting atoms and causing other electrons to be released. These new electrons also collide with other atoms, creating a

chain reaction that results in thousands of electrons leaving the channel where only a few entered. An interesting fact is that the microchannels in the MCP are created at a slight angle (about a 5-degree to 8-degree bias) to encourage electron collisions and reduce both ion and direct-light feedback from the phosphors on the output side.

• At the end of the imageintensifier tube, the electrons hit a screen coated with phosphors.

These electrons maintain their position in relation to the channel they passed through, which

provides a perfect image since the electrons stay in the same alignment as the original photons.

The energy of the electrons causes the phosphors to reach an excited state and release photons.

These phosphors create the green image on the screen that has come to characterize night vision.

Night-vision images are known for their eerie green tint.

• The green phosphor image is viewed through another lens, 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.

Thermal Imaging

Here's how thermal imaging works:

• A special lens focuses the infrared light emitted by all of the objects in view.

• The focused light is scanned by a phased array of infrared-detector elements. The detector elements create a very detailed temperature pattern called a thermogram. It only takes about one-thirtieth of a second for the detector array to obtain the temperature information to make the

thermogram. This information is obtained from several thousand points inthe field of view of the detector array.

• The thermogram created by the detector elements is translated into electric impulses.

• The impulses are sent to a signal-processing unit, a circuit board with a dedicated chip that translates the information from the elements into data for the display.

• 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 the elements creates the image.

The basic components of a thermal-imaging system

Types of Thermal Imaging Devices

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

(2,000C) and can normally detect changes in temperature of about 0.4 F (0.2 C).

Night vision Report page 1 of 7

CONTENTS

Ø INTRODUCTION Ø WHAT IS NIGHT VISION Ø HISTORY Ø BASICS Ø HOW IT WORKS Ø IMAGE ENHANCEMENT Ø THERMAL IMAGING Ø GENERATIONS Ø EQUIPMENTS Ø APPLICATIONS Ø ADVANTAGES Ø DISADVANTAGES Ø CONCLUSION Ø FUTURE SCOPE

INTRODUCTION

Night vision technology, by definition, literally allows one to see in the dark. Originally

developed for military use, it has provided the United States with a strategic military

advantage, the value of which can be measured in lives. Federal and state agencies now

routinely utilize the technology for site security, surveillance as well as search and

rescue. Night vision equipment has evolved from bulky optical instruments in lightweight

goggles through the advancement of image intensification technology.

The first thing you probably think of when you see the words night vision is a spy or

action movie you've seen, in which someone straps on a pair of night-vision goggles to

find someone else in a dark building on a moonless night. And you may have wondered

"Do those things really work? Can you actually see in the dark?"

The answer is most definitely yes. With the proper night-vision equipment, you can see a

person standing over 200 yards (183 m) away on a moonless, cloudy night! Night vision

can work in two very different ways, depending on the technology used.

• Image enhancement - This works by collecting the tiny amounts of light,

including the lower portion of the infrared light spectrum, that are present but

may be imperceptible to our eyes, and amplifying it to the point that we can

easily observe the image.

• Thermal imaging - This technology operates by capturing the upper portion

of the infrared light spectrum, which is emitted as heat by objects instead of

simply reflected as light. Hotter objects, such as warm bodies, emit more of this

light than cooler objects like trees or buildings.

Night Vision approaches

Types of ranges

Spectral range

Night-useful spectral range techniques can sense radiation that is invisible to a human observer. Human vision is confined to a small portion of the electromagnetic spectrum called visible light. Enhanced spectral range allows the viewer to take advantage of non-visible sources of electromagnetic radiation (such as near-infrared or ultraviolet radiation). Some animals can see using much more of the infrared and/or ultraviolet spectrum than humans.

Intensity range

Sufficient intensity range is simply the ability to see with very small quantities of light. Although the human visual system can, in theory, detect single photons under ideal conditions, the neurological noise filters limit sensitivity to a few tens of photons, even in ideal conditions.

Many animals have better night vision than humans do, the result of one or more differences in the morphology and anatomy of their eyes. These include having a larger eyeball, a larger lens, a larger optical aperture (the pupils may expand to the physical limit of the eyelids), more rods than cones (or rods exclusively) in the retina, a tapetum lucidum.

Enhanced intensity range is achieved via technological means through the use of an image intensifier, gain multiplication CCD, or other very low-noise and high-sensitivity array of photodetectors.

NIGHT VISION TECHNOLOGY Slide layers

Introduction
Types of NVT
Thermal Imaging
Image Enhancement
Performance Attributes
Technical characteristics
Equipments
Applications
Conclusion
References

Introduction
NVT allows us to see in the dark
Originally developed for military use
Now used for site security, surveillance as well as search and rescue
Evolved from bulky optical instruments in lightweight goggles through the advancement of image intensification technology.
Types of night vision
Categorized by generations
Each substantial change NVT establishes a new generation
Categorized into:
Generation-0
Generation-1
Generation-2
Generation-3
Generation-4

Generation-0
Created by US Army
Uses active infrared
A projection unit called IR illuminator is attached
Full moon operation
Use anode in conjunction with cathode to accelerate the electrons
Problems “acceleration causes distortion of image as well as reduction of life of the tube
Also, it was quickly duplicated by the hostile nations

Generation-1 (1960™s)
Uses passive infrared
Uses ambient light provided by the moon and the stars
Don™t require a source of projected infrared light
Don™t work well on cloudy or moonless nights
One quarter moon operation
Uses same image-intensifier tube technology as Generation-0
Same problems as faced by the Generation-0

Generation-2 (1970™s)
Offer improved resolution and performance over Generation-1 devices
Considerably more reliable
Able to see in extreme low light conditions due to the addition of microchannel plate(MCP) to the image-intensifier tube
The images are less distorted and brighter

 

Generation-3 (1990™s)
Currently used by the US Army
Better resolution and sensitivity
Photocathode is made up of Gallium Arsenide
MCP is coated with an ion barrier
Tube life is increased
Generation-4 (2000™s)
Known as filmless and gated technology
Shows significant improvement in both high- and low-level light environments
No ion barrier in MCP
Responds quickly to different lightning conditions
Reduced background noise
Enhances signal to noise ratio
Images are less distorted and brighter

Thermal imaging
This technology operates by capturing upper portion of the infrared light spectrum, which is emitted as heat
Hotter objects emit more of this light than the cooler objects
These elements then create a thermogram
Thermogram electric pulses display data

Thermal imaging
Thermal imaging devices
Two types:
1. Uncooled.
2. Cryogenically cooled.

Great for detecting people or working in near-absolute darkness

Image Enhancement
Image Enhancement
It is also known as Image intensification
Relies on image intensifier tube to collect an amplify infrared and visible light
Lens captures the light which is then sent to image intensifier tube
It has photocathode that converts photons into electrons
When electrons pass through MCP ,more electrons are presented
This causes chain reaction where atoms are released
Electrons reach phosphor screen and photons are released
Those phosphor create green image

Performance Attributes
Sensitivity (photo response)- tube™s ability to detect the available light
Signal- plays a key role in night vision™s performance
Resolution- ability to dissolve detail in the image
Technical Characteristics
Textures, Light and Dark
Depth Perception
Fog and Rain
Honeycomb
Spots
Equipments
Three categories
Scopes
Goggles
Cameras

Equipments
Scopes- monocular, handheld, better look at a specific object and then return to normal viewing conditions.
Goggles- binocular, handheld or worn, excellent for constant viewing
Cameras- send the image to a monitor for display or to a VCR for recording.

 

Applications
Military
Law enforcement
Hunting
Wild life observation
Surveillance
Security
Navigation
Hidden-object detection
Entertainment

Conclusions
Although the term ``night vision'' currently encompasses three distinct technologies, it is the evolution of image intensification technology that first made devices practical and widely used.

Their success was the result of advancements in light amplification and resolution techniques.
References

http://electronics.howstuffworks.com/nightvision3.html
http://www.nightvision.com/military/militaryhome.html
http://www.physics.ohio-state.edu/~wilki...index.html
http://www.atncorp.com/HowNightVisionWorks
http://www.morovision.com/hownightvisionworks.htm
http://www.alanaecology.com/acatalog/Introduction_to_ Nightvision.html

NIGHT VISION

ABSTRACT

Submitted by

Sadekur Rahaman ECE-29/08

Debayan Kabiraj ECE-37/08

Night vision technology, by definition, literally allows one to see in the dark, it helps humans see in what we call the dark. Humans see in only a small part of the light spectrum. Light is made of waves of energy and the longer the wave is, the less energy it has. The shorter a wave is, the more energy it contains which means that the visible light we see has a range of energy levels. Red is the lowest. Violet has the highest energy. The color spectrum increases in energy as you go from red, orange, yellow, green, blue, indigo, and the highest violet. Below the visible red waves, we can see are even lower energy waves called infrared. We can also call these heat waves. The infrared part of the light spectrum can be divided into three types. Near infrared is closest to visible red light. Mid infrared waves are longer and farther away from visible red light. Thermal infrared has longer wavelengths still. Violet is the highest visible wavelength, which humans can see. Above the violet colored waves, we see in the visible light spectrum, are the ultra violet waves, which has higher energy waves than

Visible violet light.
Night vision devices can help us to see a great distance away on a cloudy night when there is no moon light and it works in two ways.
One way uses light that that we cannot see toward the infrared end of the light spectrum. This light is amplified to the point where we can see images.
A lens focuses visible and infrared light into a special electronic tube that intensifies a dim image into a strong one. The few photons that exist in the dim light are converted to electrons. The electrons, pushed by a strong voltage within the tube, collide with the sides of the slightly bent tube to create thousands of electrons. Electrons hitting other electrons in the micro channels of the vacuum tube generate thousands more electrons than there were to start with. There is a screen covered with phosphors at the end of the tube. When the electrons hit the phosphors they become excited. A greenish light is given off in the image of what there is

to be seen.

Another way night vision is achieved is by using the heat objects give off. This is how thermal imaging works. The light given off by warm objects is focused by a specially designed lens. This infrared light hits an electronic detector device, which creates a detailed pattern of the differences in temperature. This pattern is called a thermogram. The information held in the thermogram is transformed into electrical impulses. A little computer creates usable data from the electrical impulses and the data is processed more and sent to a display where it is seen as various colors, depending on how much infrared light an object was giving off. There must be a temperature difference between objects and their surroundings to detect images. This image can be viewed through a scope like in a pair of binoculars or on a monitor screen.

NVD Evolved from bulky optical instruments in lightweight goggles through the advancement of image intensification technology. Types of night vision Categorized by generations each substantial change NVT establishes a new generation

Categorized into:

Generations	Invention Time	Uses
Generation 0	The earliest (1950's)	Created by US Army Uses active infrared.
Generation 1	1960's (Vietnam Era)	Uses passive infrared Uses ambient light provided by the moon and the stars.
Generation 2	late 1970s and early 1980s	Offer improved resolution and performance over Generation-1 devices.
Generation 3	1990	Uses the gallium arsenide (GaAs) photocathode and the ion-barrier Film on the MCP.
Generation 4	2000	Known as filmless and gated technology Shows significant improvement in both high- and low-level light environments.

The original purpose of night vision was to locate enemy targets at night. It is still used extensively by the military for that purpose, as well as for navigation, surveillance and targeting. Police and security often use both thermal-imaging and image-enhancement technology, particularly for surveillance. Hunters and nature enthusiasts use NVDs to maneuver through the woods at night. Detectives and private investigators use night vision to watch people they are assigned to track. Many businesses have permanently-mounted cameras equipped with night vision to monitor the surroundings.