Night Vision
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#1
21-09-2008, 10:00 AM


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.
The Micro Channel Plates are applicable only to image enhancement type of night vision equipments.


The original purpose of night vision was to locate enemy targets at night. Added advantages provided by the micro channel plate technology has helped in constructing night vision equipments with reduced size, weight and improved performance characteristics compared to conventional cascade tube based image intensifiers.


New generation image intensifier tubes have improved gains, and yet are one-tenth the size and one-third the cost of earlier tubes. The application of micro channel plates in night vision equipments will certainly help to improve the chances of safety and security provided to the user...
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#2
11-02-2009, 04:17 PM


.pdf   NIGHT VISION TECHNOLOGY seminar report.pdf (Size: 425.92 KB / Downloads: 608)
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Night Vision Technology
Definition
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. 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.

To study about night vision technology we should first know about ligt.
The amount of energy in a light wave is related to its wavelength: Shorter wavelengths have higher energy. Of visible light, violet has the most energy, and red has the least. Just next to the visible light spectrum is the infrared spectrum.
Night vision technology consists of two major types: light amplification (or intensification) and thermal (infrared).
Most consumer night vision products are light amplifying devices. All ITT Night Vision products use light-amplifying technology.

This technology takes the small amount of light that's in the surrounding area (such as moonlight or starlight), and converts the light energy (scientists call it photons) into electrical energy (electrons).
These electrons pass through a thin disk that's about the size of a quarter and contains more than 10 million channels. As the electrons go through the channels, they strike the channel walls and thousands more electrons are released. These multiplied electrons then bounce off of a phosphor screen which converts the electrons back into photons and lets you see an impressive nighttime view even when it's really dark.

In night vision, thermal imaging takes advantage of this infrared emission.

Thermal imaging works as
1. A special lens focuses the infrared light emitted by all of the objects in view.
2. 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 in the field of view of the detector array.
3. The thermogram created by the detector elements is translated into electric impulses.
4. 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.
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 the elements creates the image.

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


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#3
15-02-2009, 12:16 AM

he 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.

In this article, you will learn about the two major night-vision technologies. We'll also discuss the various types of night-vision equipment and applications. But first, let's talk about infrared light.
Infrared Light

In order to understand night vision, it is important to understand something about light. The amount of energy in a light wave is related to its wavelength: Shorter wavelengths have higher energy. Of visible light, violet has the most energy, and red has the least. Just next to the visible light spectrum is the infrared spectrum.
[img]static.howstuffworksgif/nightvision2.gif[/img]
light spectrum
Infrared light is a small part of the light spectrum.

Infrared light can be split into three categories:

* Near-infrared (near-IR) - Closest to visible light, near-IR has wavelengths that range from 0.7 to 1.3 microns, or 700 billionths to 1,300 billionths of a meter.
* Mid-infrared (mid-IR) - Mid-IR has wavelengths ranging from 1.3 to 3 microns. Both near-IR and mid-IR are used by a variety of electronic devices, including remote controls.
* Thermal-infrared (thermal-IR) - Occupying the largest part of the infrared spectrum, thermal-IR has wavelengths ranging from 3 microns to over 30 microns.

The key difference between thermal-IR and the other two is that thermal-IR is emitted by an object instead of reflected off it. Infrared light is emitted by an object because of what is happening at the atomic level.

Atoms
Atoms are constantly in motion. They continuously vibrate, move and rotate. Even the atoms that make up the chairs that we sit in are moving around. Solids are actually in motion! Atoms can be in different states of excitation. In other words, they can have different energies. If we apply a lot of energy to an atom, it can leave what is called the ground-state energy level and move to an excited level. The level of excitation depends on the amount of energy applied to the atom via heat, light or electricity.

An atom consists of a nucleus (containing the protons and neutrons) and an electron cloud. Think of the electrons in this cloud as circling the nucleus in many different orbits. Although more modern views of the atom do not depict discrete orbits for the electrons, it can be useful to think of these orbits as the different energy levels of the atom. In other words, if we apply some heat to an atom, we might expect that some of the electrons in the lower energy orbitals would transition to higher energy orbitals, moving farther from the nucleus.
[img]static.howstuffworksgif/nightvision-atom.jpg[/img]
atom
An atom has a nucleus and an electron cloud.

Once an electron moves to a higher-energy orbit, it eventually wants to return to the ground state. When it does, it releases its energy as a photon -- a particle of light. You see atoms releasing energy as photons all the time. For example, when the heating element in a toaster turns bright red, the red color is caused by atoms excited by heat, releasing red photons. An excited electron has more energy than a relaxed electron, and just as the electron absorbed some amount of energy to reach this excited level, it can release this energy to return to the ground state. This emitted energy is in the form of photons (light energy). The photon emitted has a very specific wavelength (color) that depends on the state of the electron's energy when the photon is released.

Anything that is alive uses energy, and so do many inanimate items such as engines and rockets. Energy consumption generates heat. In turn, heat causes the atoms in an object to fire off photons in the thermal-infrared spectrum. The hotter the object, the shorter the wavelength of the infrared photon it releases. An object that is very hot will even begin to emit photons in the visible spectrum, glowing red and then moving up through orange, yellow, blue and eventually white. Be sure to read How Light Bulbs Work, How Lasers Work and How Light Works for more detailed information on light and photon emission.

In night vision, thermal imaging takes advantage of this infrared emission. In the next section, we'll see just how it does this.
Thermal Imaging
Here's how thermal imaging works:

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

2. 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 in the field of view of the detector array.

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

4. 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.

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 the elements creates the image.
[img]static.howstuffworksgif/nightvision-thermal.jpg[/img]
thermal imaging system
Image courtesy of Infrared, Inc.
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 (2,000 C), and can normally detect changes in temperature of about 0.4 F (0.2 C).
[img]static.howstuffworksgif/nightvision-normal.jpg[/img][img]static.howstuffworksgif/nightvision-night2.jpg[/img][img]static.howstuffworksgif/nightvision-night.jpg[/img]
day
Image courtesy of Infrared, Inc.
It is quite easy to see everything during the day...

night
Image courtesy of Infrared, Inc.
...but at night, you can see very little.
thermal imaging
Image courtesy of Infrared, Inc.
Thermal imaging lets you see again.

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 darkness, most night-vision equipment uses image-enhancement 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.
[img]static.howstuffworksgif/nightvision-tube.jpg[/img]
image intensifier tube
The image-intensifier tube changes photons to electrons and back again.

Here's how image enhancement works:

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. 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.

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

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 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.
[img]static.howstuffworksgif/nightvision-caught.jpg[/img]
night vision image
Photo courtesy of B.E. Meyers Company
Night-vision images are known for their eerie green tint.
5. At the end of the image-intensifier 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.

6. 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.
Generations
NVDs have been around for more than 40 years. They are categorized by generation. Each substantial change in NVD technology establishes a new generation.
7. Generation 0 - The original night-vision system created by the United States Army and used in World War II and the Korean War, these NVDs use active infrared. This means that a project and implimentationion unit, called an IR Illuminator, is attached to the NVD. The unit project and implimentations a beam of near-infrared light, similar to the beam of a normal flashlight. Invisible to the naked eye, this beam reflects off objects and bounces back to the lens of the NVD. These systems use an anode in conjunction with the cathode to accelerate the electrons. The problem with that approach is that the acceleration of the electrons distorts the image and greatly decreases the life of the tube. Another major problem with this technology in its original military use was that it was quickly duplicated by hostile nations, which allowed enemy soldiers to use their own NVDs to see the infrared beam project and implimentationed by the device.

8. Generation 1 - The next generation of NVDs moved away from active infrared, using passive infrared instead. Once dubbed Starlight by the U.S. Army, these NVDs use ambient light provided by the moon and stars to augment the normal amounts of reflected infrared in the environment. This means that they did not require a source of project and implimentationed infrared light. This also means that they do not work very well on cloudy or moonless nights. Generation-1 NVDs use the same image-intensifier tube technology as Generation 0, with both cathode and anode, so image distortion and short tube life are still a problem.

9. Generation 2 - Major improvements in image-intensifier tubes resulted in Generation-2 NVDs. They offer improved resolution and performance over Generation-1 devices, and are considerably more reliable. The biggest gain in Generation 2 is the ability to see in extremely low light conditions, such as a moonless night. This increased sensitivity is due to the addition of the microchannel plate to the image-intensifier tube. Since the MCP actually increases the number of electrons instead of just accelerating the original ones, the images are significantly less distorted and brighter than earlier-generation NVDs.

10. Generation 3 - Generation 3 is currently used by the U.S. military. While there are no substantial changes in the underlying technology from Generation 2, these NVDs have even better resolution and sensitivity. This is because the photo cathode is made using gallium arsenide, which is very efficient at converting photons to electrons. Additionally, the MCP is coated with an ion barrier, which dramatically increases the life of the tube.

11. Generation 4 - What is generally known as Generation 4 or "filmless and gated" technology shows significant overall improvement in both low- and high-level light environments.

The removal of the ion barrier from the MCP that was added in Generation 3 technology reduces the background noise and thereby enhances the signal to noise ratio. Removing the ion film actually allows more electrons to reach the amplification stage so that the images are significantly less distorted and brighter.

The addition of an automatic gated power supply system allows the photocathode voltage to switch on and off rapidly, thereby enabling the NVD to respond to a fluctuation in lighting conditions in an instant. This capability is a critical advance in NVD systems, in that it allows the NVD user to quickly move from high-light to low-light (or from low-light to high-light) environments without any halting effects. For example, consider the ubiquitous movie scene where an agent using night vision goggles is sightless when someone turns on a light nearby. With the new, gated power feature, the change in lighting wouldnâ„¢t have the same impact; the improved NVD would respond immediately to the lighting change.

Many of the so-called "bargain" night-vision scopes use Generation-0 or Generation-1 technology, and may be disappointing if you expect the sensitivity of the devices used by professionals. Generation-2, Generation-3 and Generation 4 NVDs are typically expensive to purchase, but they will last if properly cared for. Also, any NVD can benefit from the use of an IR Illuminator in very dark areas where there is almost no ambient light to collect.
[img]static.howstuffworksgif/nightvision-lens.jpg[/img]
NVD camera
Photo courtesy of B.E. Meyers Company
NVDs come in a variety of styles, including ones that can be mounted to cameras.

A cool thing to note is that every single image-intensifier tube is put through rigorous tests to see if it meets the requirements set forth by the military. Tubes that do are classified as MILSPEC. Tubes that fail to meet military requirements in even a single category are classified as COMSPEC.
Night Vision Equipment and Applications
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.
[img]static.howstuffworksgif/nightvision3.jpg[/img]
pocketscope
Photo courtesy of B.E. Meyers Company
DARK INVADER Multi-purpose Pocketscope

* 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.

goggles
Photo courtesy of B.E. Meyers Company
DARK INVADER Night-vision Goggles 4501

* 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.
[img]static.howstuffworksgif/nightvision-camera.jpg[/img][img]static.howstuffworksgif/nightvision-goggles.jpg[/img]
video camera
Photo courtesy of B.E. Meyers Company
Stealth 301 Series Day/Night Video Camera

Applications
soldier goggles
Photo courtesy of B.E. Meyers Company
This soldier is using DARK INVADER night-vision goggles.
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.

camcorder
Photo courtesy of B.E. Meyers Company
Camcorders are a fast-growing segment
of the night-vision industry.

Many people are beginning to discover the unique world that can be found after darkness falls. If you're out camping or hunting a lot, chances are that night-vision devices can be useful to you -- just be sure to get the right type for your needs.

For more information on night vision and related topics, check out the links on the next page.
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22-02-2010, 06:04 AM

Thanks for making such a contribution. Here i contribute my seminar and presentation power point presentation on topic night vision technology.
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15-03-2010, 08:05 PM


.ppt   Night Vision Technology.ppt (Size: 2.7 MB / Downloads: 1,197)

Night Vision Technology
Development through Military History into Modern Daily Use.
Introduction

Night vision technology has shaped history.
Pre 1940â„¢s: Flares and spot lights were used for operations at night.
Introduction Cont.
Due to the nature of these early night vision devices (NVD), they gave away tactical positions.
Military scientists began to think of ways to improve night vision to gain a strategic advantage.
Introduction Cont.
A tank from World War II equipped with a search light used for night combat.
Early Development
The first night vision devices (NVD) were created during WWII.
Functioned by placing an infrared filter over a searchlight.
Fighters would use special binoculars to see using the light from the searchlights.
Many problems came from this night vision method.
NVD FUN POP QUIZ!
Why do NVD devices always show images in hues of green
And the answer is¦¦
C
The screen was purposefully colored green due to the scientific fact that the human eye can differentiate more shades of green that any other color.
Early Development Cont.
There were many disadvantages to using the searchlights and flares.
The actual searchlight was massive and had to be mounted on a truck or tank.
Both the Allies and Naziâ„¢s had this technology, so they each could see the others light.
Early Development Cont.
The images created were streaky and distorted.
The acceleration of electrons cut the life of the image intensification tube, which was the most important and expensive part of the NVD, very short.
Military scientists began planning a revised design.
Generation 1
Post WWII NVD technology focused on the ability to see without creating additional light.
During this time period the first Generation of NVD began using intensified natural lighting.
Generation 1 Cont.
Military scientists created a two-stage cascade image tube.
This tube intensified the natural lighting and created a superior image for the viewer.
The power of Generation 1 NVD was put to the test in the Vietnam War.
NVD FUN POP QUIZ 2
Generation 1 NVD were commonly called what during their use in the Vietnam War
And the Answer is¦
A
Star-Tron Scopes was the common name given to the NVD in Vietnam.
There were still many problems military scientists wanted to work on.
Generation 1 Cont.
Star Tron Scopes intensification tubes were as heavy as the rifles they were mounted on.
They were not sensitive enough to give clear images in anything less than full moonlight.
The NVD emitted a whiney noise.
They would shut down if they were exposed to a sudden burst of bright light.
Generation 2
There were two major developments in NVD technology after their test in Vietnam.
The first was a new micro-channel plate (MPC) that was light weight, and more effective at focusing light into clear images.
The second major development was the invention of thermal imagining.
Generation 2 Cont.
Thermal imaging allowed for NV even through low natural lighted conditions.
It also allowed for NV through smoky, dusty, and foggy conditions.
These thermal imagers were expensive, so in 1973 scientists created a common module that made it less expensive, and more ideal for military use.
Generation 2 Cont.
The generation 2 NVD were first put to the test by US forces in the early 1990â„¢s during Operation Desert Storm in Kuwait.
The dark nights and harsh dusty conditions were perfect for implementing the new technology.
Current Generations
The currently generations of NVS are generations 3 and 4.
Generation 3 is much like generation 2 except for it has a substantially longer life, as well as more defined images.
Generation 4 has less noise than generation 3, however it has shorter life.
Current Generations Cont.
Here is a chart comparing the life in hours of the intensification tube for generations 1-3
LAST NVD FUN POP QUIZ!
Which of the 4 Generations of NVD is the current model used by the U.S. Military
And the answer is¦
General Public Use
Development of NVD up until the 1980â„¢s was completely focused around military purposes.
In the 80â„¢s, companies in the US and Europe took NVT and found ways to improve everyday civilian life.
General Public Use Cont.
There are many practical everyday uses for NVD, some of which are:
Law Enforcement
Hunting
Surveillance
General Public Use Cont.
Security
Navigation
Hidden-Object detection
Entertainment
Conclusion

In conclusion I believe that is wonderful how something originally designed for destruction, can now help people on an every-day basis.
Personally, NVD have saved my brother-in-law from harm in his job through NVD navigation technology.
This is truly amazing technology.
References
Unknown author, Night Vision Devices. BookRags. 11/12/2008
<bookrags.com>
Unknown author, Night Vision Goggles. GlobalSecurity. 11/10/2008
<global securities.org>
Unknown author, How Night Vision Works. How Stuff Works. 11/11/2008
<electronics.howstuffworks.com>
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10-04-2010, 10:02 PM

please read topicideashow-to-night-vision-technology-a-seminar and presentation-report for more of Night Vision Related information
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14-04-2011, 03:15 PM


.doc   night vision.doc (Size: 857 KB / Downloads: 49)
PAPER PRESENTATION-2011
NIGHT VISION TECHNOLOGY


PRESENTED BY:
RAHAMATH ALI.S/2K9675
CSE DEPT-2nd YEAR
CAHCET
VELLORE




ABSTRACT:

A night vision device (NVD) is an optical installment that allows images to be produced in levels of light approaching total darkness. They are most often used by the military and law enforcement agencies, but are available to civilian users. The term usually refers to a complete unit, including an image intensifier tube, a protective and generally water-resistant housing, and some type of mounting system. Many NVDs also include sacrificial lenses, IR illuminators, and telescopic lenses. NVDs are mounted appropriately for their specific purpose, with more general- purpose devices having more mounting options. For instance, the AN/PVS-14 is a monocular night vision device in use with the US military as well as by civilians. It may be mounted on the user's head for hands free use with a harness or helmet attachment, either as a monocular device, or in aligned pairs for binocular "night vision goggles" which provide a degree of depth perception as do optical binoculars. The AN/PVS-14 may also be attached to a rifle using a Pica tinny rail, in front of an existing telescopic or red dot sight, or attached to a single-lens reflex camera. Other systems, such as the AN/PVS-22 or Universal Night Sight, are designed for a specific purpose, integrating an image intensifier into, for example, a telescopic sight, resulting in a smaller and lighter but less versatile system
INTRDUCTION:
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 sanding 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.



In this article, you will learn about the two major night-vision technologies. We'll also
discuss the various types of night-vision equipment and applications. But first, let's talk about infrared light.
THE BASICS:

In order to understand night vision, it is important to understand something about light. The amount of energy in a light wave is related to its wavelength: Shorter wavelengths have higher energy. Of visible light, violet has the most energy, and red has the least. Just next to the visible light spectrum is the infrared spectrum.
Infrared light can be split into three categories:
• Near-infrared (near-IR) - Closest to visible light, near-IR has wavelengths
that range from 0.7 to 1.3 microns, or 700 billionths to 1,300 billionths of a
meter.
• Mid-infrared (mid-IR) - Mid-IR has wavelengths ranging from 1.3 to 3
microns. Both near-IR and mid-IR are used by a variety of electronic devices,
including remote controls.
• Thermal-infrared (thermal-IR) - Occupying the largest part of the infrared
spectrum, thermal-IR has wavelengths ranging from 3 microns to over 30
microns.


Generations:
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 1 illustrates first-generation night vision. [Not a great topic sentence but it does has the advantage of calling attention to the figure.] 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.

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. [These two
sentences could have been combined: "Figure2 depicts how second-generation image ...
plate."] 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.
[No topic sentence. Indeed one might have moved this material to the front in a more
dramatic way, perhaps by calling attention to the movie `Silence of the Lambs.'] slight
green tint similar to some sunglasses. The apparent lighting of the landscape on a dark night is comparable to what the unaided eye would see on a clear winter night with fresh snow 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.

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.
1. Textures, Light and Dark
2. Depth Perception
3. Fog and Rain
4. Honeycomb
5. Black Spots



Equipment and Applications:

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.

Applications:

Common applications for night vision include:
• Military
• Law enforcement
• Hunting
• Wildlife observation
• Surveillance
• Security
• Navigation
• Hidden-object detection
• Entertainment
Night vision Home Security Camera

ADVANTAGES & DISADVANTAGES OF NIGHT VISION TECHNOLOGY:
ADVANTAGES:

=>Night vision devices (NVDs) provide night fighters with the ability to see, maneuver and shoot at night or during periods of reduced visibility.
=>The Army used two different types of NVDs – image intensifiers and thermals. =>Image-Intensifying Devices are based upon light amplification and must have some light available.
=>These devices can amplify the available light from 2,000 to 5,000 times. Thermal Forward-Looking Infrared (FLIR) detectors – sometimes called “sensors” – work by sensing the temperature difference between an object and its environment.
=>FLIR systems are installed on certain combat vehicles and helicopters.
DIS-ADVANTAGES:

=>The main dis advantage is we are loosing our direct contact of eye by this technology.
=>The another dis advantage is we are forgetting the present world & thinking the entirely different future world so that we are not taking care of present world technology.
CONCLUTION:

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.
REFERENCE:

electronics.howstuffworksnightvision3.html
nightvisionmilitary/militaryhome.html
physics.ohio-state.edu/~wilki...index.html
atncorpHowNightVisionWorks
morovisionhownightvisionworks.htm
alanaecologyacatalog/Introduction_to_ Nightvision.html
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