document 1

Abstract

Night vision devices provide enormous benefits. They enable

personnel to carry out operations under conditions that would

not otherwise be possible. However, these benefits carry

considerable risks. For instance, individuals often become over

confident about their ability to use image intensification and

infrared devices. In consequence, the use of night vision

equipment is an increasingly common factor in military

incidents and accidents. This paper uses an analysis of

incident and accident data to identify requirements for the

successful deployment of night vision equipment. It is argued

that these applications must be integrated more closely with

existing navigational systems. The successful application of

this technology also depends upon adequate risk assessment

and team-based training.

_______________

Oct. 16 Al Qaeda soldiers may know the terrain better and

they may be able to navigate hidden networks of underground

tunnels. But once night falls, any American troops in

Afghanistan will have at least one advantage:

They can see in the dark.

"Clearly night vision technology is essential. It's one of the

real trump cards we have in the battle with al Qaeda," said

Michael O'Hanlon, a defense specialist at the Brookings

Institution in Washington, D.C. "Otherwise, it would be a small

number of forces fighting a small number of troops on their

own turf. This is an important edge and we need every edge

we can get."

Night vision devices were invented during World War II for use

by American, British and Soviet soldiers and pilots. Since then,

the technology has evolved from bulky devices that amplify

light about 1,000 times to compact equipment that can

amplify any light source (including faint starlight) up to 50,000

times, and eyewear that allows soldiers to see in complete

darkness (such as in caves) by detecting heat differences.

Taliban May Have Some Night Vision Tech

Taliban and al Qaeda forces may have access to some night

vision equipment, bought from other countries in the past.

Last February, for example, a U.S. pilot of Egyptian origin

recounted to a New York court how he flew a private jet for

Saudi exile and alleged terrorist mastermind Osama bin Laden

and transported in equipment from Britain including night-

vision goggles.

Night vision equipment has also long been available to

consumers in the United States and elsewhere, although it is a

felony to leave the United States with the technology without

a permit.

But experts believe that any equipment al Qaeda forces may

have is scarce, and inferior to U.S. technology.

"The Taliban doesn't seem to have experience with night

vision equipment," said Anthony Cordesman, an ABCNEWS

defense consultant and senior fellow at the Center for

Strategic and International Studies. "So this equipment offers

a lot of advantages."

Some have pointed out that the Soviets had access to night

vision equipment during their drawn-out conflict with

Afghanistan in the 1980s and still the Soviets were forced to

withdraw from that conflict. But Cordesman says equipment

and training among U.S. forces far exceeds whatever Soviet

troops had more than 20 years ago.

"We have the technology," he said. "So 'We own the night'

could take on new meaning."

Already, U.S. pilots have used night vision equipment to

navigate and find targets during night bombings of

Afghanistan. Infrared lasers are also used to illuminate

targets with a light invisible to the naked eye, but visible to

those using infrared detection technology. Infrared images are

portrayed in shades of color onto a TV screen in the cockpit.

"Being able to operate around the clock, in the day and the

night, is vital for the air forces because it places great

uncertainty in the minds of the opposition," said Nick Cook,

aviation consultant for Jane's Defense Weekly.

Amplifying Light, Seeing by Temperatures

Night vision equipment falls into two major categories: image

intensification systems and thermal devices.

Even when a night appears completely dark, near-infrared

light is emitted by the moon and stars. A night vision device

amplifies this light to visible levels. The light, which is made

up of photons, is converted into electrical energy and then

accelerated through a thin disk called a microchannel plate.

As the converted photons strike a phosphorus screen as

electrons, they are perceived through an eyepiece in shades of

green.

"The reason it's in green is because when you put the unit

down, you want your eyes to remain dilated so you can see in

dim light," said Rich Urich, director of operations at Night

Vision Equipment Company in Prescott Valley, Ariz. "Use most

any other color and your pupils will constrict when you take

off the unit."

Infrared technology measures fraction of a degree differences

of heat given off by objects. All living things and many objects

people, animals, recently used cars emit heat in the form

of infrared radiation. Infrared radiation is a part of the

electromagnetic spectrum just below ("infra") the frequency of

red light. Infrared devices read heat by absorbing infrared

light, converting it into a grid of video signals and creating a

picture the viewer can see.

Effective in Winter

Urich explains, while viewing through an infrared device:

"you'll see varying shades of gray or black, with the whitest

segments representing those giving off the most heat." Some

reports have suggested that infrared technology will become

more effective as winter arrives in Afghanistan, since

contrasts between body temperatures and the external

temperatures will increase. But Urich claims the contrast

doesn't necessarily enhance infrared images, and once snow

falls, the opposite is true.

"Infrared systems are very sensitive to white," he says. "The

images can be compromised if there is snow everywhere."

Infrared devices might not only prove useful to ground troops

and pilots for vision, they can also help detect recent

footprints or tire tracks that could still be emitting heat. Even

objects that have recently been touched, like a desk or door,

can show traces of the recent activity.

Besides military use, infrared technology has proven useful in

many other applications. Law enforcement use it to detect

criminals operating at night, border patrol use it to monitor for

illegal crossings, ranchers use it to hunt nocturnal predators

such as coyotes and drivers in some specially-outfitted

automobiles use it for better vision during night driving. The

technology can also help create a thermal image of a home to

find leaks and improve insulation.

____________

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.

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.

Biometrics, Fire Alarms, Wireless

The use of night vision cameras continues to expand as home

owners in particular realize the importance of maintaining

total coverage of their property. Night time conditons provide

an ideal scenario for intruders to invade your space and steal

your property but with the right equipment, they are kept

under a watchful eye. The other important use for night vision

cameras is keeping an eye on children. Young infants can be

monitored in virtual total darkness. In this article, we'll

examine some solutions for both the exterior and interior of

your property.Indoor Wireless Camera CoverageThe IR

wireless Night Vison camera is ideal for indoor surveillance. At

less than $300, it's manoevrability makes it practical for

keeping an eye on areas of the house which are difficult to

survey with cabled cameras.As mentioned above, keeping a

close watch on infants especially during times when there are

concerns about their health is always a challenge for parents.

A wireless security camera with infrared capability can ease a

lot of that concern.Outdoor Night Vision CoverageThere are

areas around most homes which are considered prime entry

spots for intruders. During daytime conditions, there is less

concern but when the sun sets, that concern will be

heightened.These "blind spots" can be monitored with night

vision security cameras. When looking for the right camera,

make sure it has weather resistant qualities. Security cameras

such as the Weatherproof Day/Night Bullet Color Camera are

serviceable in these situations especially with a little natural

light or some street lighting.One of the important features to

look at when selecting a night vision camera is it's Lux

rating. The closer to zero this is, the better it's ability to

perform in "lightless" conditions. A zero rating would mean it

can see in total darkness. How much should you spend on a

camera with night vision ability? There is a suggestion you

can get away with good performance for less than $300

however , make sure the quality is there.There is no point in

going to the trouble of extending your security camera

coverage if you install inferior equipment. Go for good to high

quality as this can only increase your peace of mind.

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used.





observe the image.









infrared light.

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used.





observe the image.









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.

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.

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.

The basic components of a thermal-imaging system

Image courtesy of Infrared, Inc.

It is quite easy to see

everything during the

day...

Image courtesy of Infrared,

Inc.

...but at night, you can

see very little.


Inc.

Thermal imaging lets you

see again.


Inc.

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.

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).

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.

The image-intensifier tube changes photons to electrons and

back again.

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.

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.

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.

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 projection unit, called an IR Illuminator, is attached to the

NVD. The unit projects 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 projected by the device.

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 projected 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.

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.

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.

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 wouldnt 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.

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 .

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

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.

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.

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Whats The Difference between Thermal

Imaging and Night Vision?

Lets start with a little background. Our eyes see reflected

light. Daylight cameras, night vision devices, and the human

eye all work on the same basic principle: visible light energy

hits something and bounces off it, a detector then receives it

and turns it into an image.

Whether an eyeball, or in a camera, these detectors must

receive enough light or they cant make an image. Obviously,

there isnt any sunlight to bounce off anything at night, so

theyre limited to the light provided by starlight, moonlight

and artificial lights. If there isnt enough, they wont do much

to help you see.

Thermal Imaging Cameras

Thermal imagers are altogether different. In fact, we call them

cameras but they are really sensors. To understand how

they work, the first thing you have to do is forget everything

you thought you knew about how cameras make pictures.

FLIRs make pictures from heat, not visible light. Heat (also

called infrared , or thermal , energy) and light are both parts of

the electromagnetic spectrum, but a camera that can detect

visible light wont see thermal energy, and vice versa.

Thermal cameras detect more than just heat though; they

detect tiny differences in heat as small as 0.01C and

display them as shades of grey in black and white TV video.

This can be a tricky idea to get across, and many people just

dont understand the concept, so well spend a little time

explaining it.

Everything we encounter in our day-to-day lives gives off

thermal energy, even ice. The hotter something is the more

thermal energy it emits. This emitted thermal energy is called

a heat signature. When two objects next to one another have

even subtly different heat signatures, they show up quite

clearly to a FLIR regardless of lighting conditions.

Thermal energy comes from a combination of sources,

depending on what you are viewing at the time. Some things

warm-blooded animals (including people!), engines, and

machinery, for example create their own heat, either

biologically or mechanically. Other things land, rocks, buoys,

vegetation absorb heat from the sun during the day and

radiate it off during the night.

Because different materials absorb and radiate thermal energy

at different rates, an area that we think of as being one

temperature is actually a mosaic of subtly different

temperatures. This is why a log thats been in the water for

days on end will appear to be a different temperature than the

water, and is therefore visible to a thermal imager. FLIRs

detect these temperature differences and translate them into

image detail.

While all this can seem rather complex, the reality is that

modern thermal cameras are extremely easy to use. Their

imagery is clear and easy to understand, requiring no training

or interpretation. If you can watch TV, you can use a FLIR

thermal camera.

Night Vision Devices

Those greenish pictures we see in the movies and on TV come

from night vision goggles (NVGs) or other devices that use

the same core technologies. NVGs take in small amounts of

visible light, magnify it greatly, and project that on a display.

Cameras made from NVG technology have the same

limitations as the naked eye: if there isnt enough visible light

available, they cant see well. The imaging performance of

anything that relies on reflected light is limited by the amount

and strength of the light being reflected.

NVG and other lowlight cameras are not very useful during

twilight hours, when there is too much light for them to work

effectively, but not enough light for you to see with the naked

eye. Thermal cameras arent affected by visible light, so they

can give you clear pictures even when you are looking into the

setting sun. In fact, you can aim a spotlight at a FLIR and still

get a perfect picture.

Infrared Illuminated (I ) Cameras

I cameras try to generate their own reflected light by

projecting a beam of near-infrared energy that their imager

can see when it bounces off an object. This works to a point,

but I cameras still rely on reflected light to make an image,

so they have the same limitations as any other night vision

camera that depends on reflected light energy short range,

and poor contrast.

Contrast

All of these visible light cameras daylight cameras, NVG

cameras, and I cameras work by detecting reflected light

energy. But the amount of reflected light they receive is not

the only factor that determines whether or not youll be able

to see with these cameras: image contrast matters, too.

If youre looking at something with lots of contrast compared

to its surroundings, youll have a better chance of seeing it

with a visible light camera. If it doesnt have good contrast,

you wont see it well, no matter how bright the sun is shining.

A white object seen against a dark background has lots of

contrast. A darker object, however, will be hard for these

cameras to see against a dark background. This is called

having poor contrast. At night, when the lack of visible light

naturally decreases image contrast, visible light camera

performance suffers even more.

Thermal imagers dont have any of these shortcomings. First,

they have nothing to do with reflected light energy: they see

heat. Everything you see in normal daily life has a heat

signature. This is why you have a much better chance of

seeing something at night with a thermal imager than you do

with visible light camera, even a night vision camera.

In fact, many of the objects you could be looking for, like

people, generate their own contrast because they generate

their own heat. Thermal imagers can see them well because

they dont just make pictures from heat; they make pictures

from the minute differences in heat between objects.

Night vision devices have the same drawbacks that daylight

and lowlight TV cameras do: they need enough light, and

enough contrast to create usable images. Thermal imagers, on

the other hand, see clearly day and night, while creating their

own contrast. Without a doubt, thermal cameras are the best

24-hour imaging option.

Whats The Difference between Thermal

Imaging and Night Vision?

Lets start with a little background. Our eyes see reflected

light. Daylight cameras, night vision devices, and the human

eye all work on the same basic principle: visible light energy

hits something and bounces off it, a detector then receives it

and turns it into an image.

Whether an eyeball, or in a camera, these detectors must

receive enough light or they cant make an image. Obviously,

there isnt any sunlight to bounce off anything at night, so

theyre limited to the light provided by starlight, moonlight

and artificial lights. If there isnt enough, they wont do much

to help you see.

Thermal Imaging Cameras

Thermal imagers are altogether different. In fact, we call them

cameras but they are really sensors. To understand how

they work, the first thing you have to do is forget everything

you thought you knew about how cameras make pictures.

FLIRs make pictures from heat, not visible light. Heat (also

called infrared , or thermal , energy) and light are both parts of

the electromagnetic spectrum, but a camera that can detect

visible light wont see thermal energy, and vice versa.

Thermal cameras detect more than just heat though; they

detect tiny differences in heat as small as 0.01C and

display them as shades of grey in black and white TV video.

This can be a tricky idea to get across, and many people just

dont understand the concept, so well spend a little time

explaining it.

Everything we encounter in our day-to-day lives gives off

thermal energy, even ice. The hotter something is the more

thermal energy it emits. This emitted thermal energy is called

a heat signature. When two objects next to one another have

even subtly different heat signatures, they show up quite

clearly to a FLIR regardless of lighting conditions.

Thermal energy comes from a combination of sources,

depending on what you are viewing at the time. Some things

warm-blooded animals (including people!), engines, and

machinery, for example create their own heat, either

biologically or mechanically. Other things land, rocks, buoys,

vegetation absorb heat from the sun during the day and

radiate it off during the night.

Because different materials absorb and radiate thermal energy

at different rates, an area that we think of as being one

temperature is actually a mosaic of subtly different

temperatures. This is why a log thats been in the water for

days on end will appear to be a different temperature than the

water, and is therefore visible to a thermal imager. FLIRs

detect these temperature differences and translate them into

image detail.

While all this can seem rather complex, the reality is that

modern thermal cameras are extremely easy to use. Their

imagery is clear and easy to understand, requiring no training

or interpretation. If you can watch TV, you can use a FLIR

thermal camera.

Night Vision Devices

Those greenish pictures we see in the movies and on TV come

from night vision goggles (NVGs) or other devices that use

the same core technologies. NVGs take in small amounts of

visible light, magnify it greatly, and project that on a display.

Cameras made from NVG technology have the same

limitations as the naked eye: if there isnt enough visible light

available, they cant see well. The imaging performance of

anything that relies on reflected light is limited by the amount

and strength of the light being reflected.

NVG and other lowlight cameras are not very useful during

twilight hours, when there is too much light for them to work

effectively, but not enough light for you to see with the naked

eye. Thermal cameras arent affected by visible light, so they

can give you clear pictures even when you are looking into the

setting sun. In fact, you can aim a spotlight at a FLIR and still

get a perfect picture.

Infrared Illuminated (I ) Cameras

I cameras try to generate their own reflected light by

projecting a beam of near-infrared energy that their imager

can see when it bounces off an object. This works to a point,

but I cameras still rely on reflected light to make an image,

so they have the same limitations as any other night vision

camera that depends on reflected light energy short range,

and poor contrast.

Contrast

All of these visible light cameras daylight cameras, NVG

cameras, and I cameras work by detecting reflected light

energy. But the amount of reflected light they receive is not

the only factor that determines whether or not youll be able

to see with these cameras: image contrast matters, too.

If youre looking at something with lots of contrast compared

to its surroundings, youll have a better chance of seeing it

with a visible light camera. If it doesnt have good contrast,

you wont see it well, no matter how bright the sun is shining.

A white object seen against a dark background has lots of

contrast. A darker object, however, will be hard for these

cameras to see against a dark background. This is called

having poor contrast. At night, when the lack of visible light

naturally decreases image contrast, visible light camera

performance suffers even more.

Thermal imagers dont have any of these shortcomings. First,

they have nothing to do with reflected light energy: they see

heat. Everything you see in normal daily life has a heat

signature. This is why you have a much better chance of

seeing something at night with a thermal imager than you do

with visible light camera, even a night vision camera.

In fact, many of the objects you could be looking for, like

people, generate their own contrast because they generate

their own heat. Thermal imagers can see them well because

they dont just make pictures from heat; they make pictures

from the minute differences in heat between objects.

Night vision devices have the same drawbacks that daylight

and lowlight TV cameras do: they need enough light, and

enough contrast to create usable images. Thermal imagers, on

the other hand, see clearly day and night, while creating their

own contrast. Without a doubt, thermal cameras are the best

24-hour imaging option.

______

"Night Vision" as referenced here is that technology that

provides us with the miracle of vision in total darkness and

the improvement of vision in low light environments.

This technology is an amalgam of several different methods

each having its own advantages and disadvantages. The

most common methods as described below are Low-Light

Imaging, Thermal Imaging and Near-infrared Illumination .

The most common applications include night driving or

flying, night security and surveillance, wildlife observation,

sleep lab monitoring and search and rescue. A wide range of

night vision products are available to suit the various

requirements that may exist for these applications:

Low-Light Imaging

Image intensifiers

On-chip gain multiplication cameras

Thermal Imaging

Cooled-detector infrared cameras

Uncooled-detector infrared cameras

Near Infrared Illumination

IR Illumination

Glossary of Night Vision Terms

Low-Light Imaging

Today, the most popular and well known method of performing

night vision is based on the use of image intensifiers. Image

intensifiers are commonly used in night vision goggles and

night scopes. More recently, on-chip gain multiplication CCD

cameras have become popularized for performing low-light

security, surveillance and astronomical observation.

Image Intensifiers

HOW THEY WORK: This method of night vision amplifies the

available light to achieve better vision. An objective lens

focuses available light (photons) on the photocathode of an

image intensifier. The light energy causes electrons to be

released from the cathode which are accelerated by an electric

field to increase their speed (energy level). These electrons

enter holes in a microchannel plate and bounce off the internal

specially-coated walls which generate more electrons as the

electrons bounce through. This creates a denser "cloud" of

electrons representing an intensified version of the original

image.

The final stage of the image intensifier involves electrons

hitting a phosphor screen. The energy of the electrons makes

the phosphor glow. The visual light shows the desired view to

the user or to an attached photographic camera or video

device. A green phosphor is used in these applications

because the human eye can differentiate more shades of green

than any other color, allowing for greater differentiation of

objects in the picture.

All image intensifiers operate in the above fashion.

Technological differences over the past 40 years have resulted

in substantial improvement to the performance of these

devices. The different paradigms of technology have been

commonly identified by distinct generations of image

intensifiers. Intensified camera systems usually incorporate an

image intensifier to create a brighter image of the low-light

scene which is then viewed by a traditional camera.

Image Intensifiers

Advantages Disadvantages

Excellent low-light level sensitivity.

Enhanced visible imaging yields the best possible.

recognition and identification performance.

High resolution.

Low power and cost.

Ability to identify people.

Because they are based on amplification methods,

some light is required. This method is not useful

when there is essentially no light.

Inferior daytime performance when compared to

daylight-only methods.

Possibility of blooming and damage when observing

bright sources under low-light conditions.

Image Intensifier Based Products:

Night Vision Goggles Intensified Pro-sumer Camcorders

Night Vision Pocketscopes Intensified Nikon Cameras

Intensified Professional News Cameras Intensified Canon Cameras

Intensified Removable Lens Camcorders

On-chip Gain Multiplication Cameras

HOW THEY WORK: In order to overcome some of the

disadvantages of image intensifiers, CCD image detector

manufacturers have substantially improved the sensitivity of

certain CCD detectors by incorporating an on-chip

multiplication gain technology to multiply photon-generated

charge above the detector's noise levels. The multiplication

gain takes place after photons have been detected in the

device's active area but before one of the detector's primary

noise sources (e.g. readout noise). In a new multiplication

register, electrons are accelerated from pixel-to-pixel by

applying high CCD clock voltages. As a result, secondary

electrons are generated via an impact-ionization process. Gain

can be controlled by varying the clock voltages.

Because the signal boost occurs before the charge reaches

the on-chip readout amplifier and gets added to the primary

noise source, the signal-to-noise ratio for this device is

significantly improved over standard CCD cameras and yields

low-light imaging performance far superior than traditional

CCD cameras. However, since the CCD temperature also

affects the on-chip gain multiplication (lower temperatures

yield higher gain) and because other noise sources exist that

occur before the multiplication (i.e. dark noise), it is prudent

in these systems to temperature stabilize these detectors at

temperatures about of below room temperature.

Another method for improving a CCD camera's sensitivity is to

perform averaging to reduce noise either temporally (where

sequential video frames are averaged) or spatially (where

neighboring pixels are "binned" or added together).

On-chip Gain Multiplication Cameras


High sensitivity in low-light.

Reduced likelihood of damage to the imaging

detector due to viewing bright sources.

High speed imagin capability.

Good daytime imaging performance.

High power dissipation due to the necessity to have

a temperature stabilizer.

Blooming when viewing bright sources in dark

scenes.

On-chip Gain Multiplication Camera-based Products:

Day/night surveillance camera

Frame-averaged and binned low-light CCD camera

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Thermal Imaging

Different from low-light imaging methods of night vision

(which require some ambient light in order to produce an

image), thermal imaging night vision methods do not require

any ambient light at all. They operate on the principal that all

objects emit infrared energy as a function of their temperature.

In general, the hotter an object is, the more radiation it emits.

A thermal imager is a product that collects the infrared

radiation from objects in the scene and creates an electronic

image. Since they do not rely on reflected ambient light,

thermal imagers are entirely ambient light-level independent.

In addition, they also are able to penetrate obscurants such

as smoke, fog and haze. There are two types of thermal

imaging detectors: cooled and uncooled. Cooled detector

infrared cameras require cryogenic cooling to very cold

temperatures (below 200K). Uncooled detector infrared

cameras are normally either temperature stabilized (at room

temperatures) or entirely unstabilized.

Thermal images are normally black and white in nature, where

black objects are cold and white objects are hot. Some

thermal cameras show images in color. This false color is an

excellent way of better distinguishing between objects at

different temperatures.

Cooled-detector Infrared Cameras

HOW THEY WORK: Cooled infrared detectors are typically

housed in a vacuum-sealed case and cryogenically cooled.

The detector designs are similar to other more common

imaging detectors and use semiconductor materials. However,

it is the effect of absorbed infrared energy that causes

changes to detector carrier concentrations which in turn affect

the detector's electrical properties. Cooling the detectors

(typically to temperatures below 110K, a value much lower

than the temperature of objects being detected) greatly

increases their sensitivity. Without cooling, the detectors

would be flooded by their own self-radiation.

Materials used for infrared detection include a wide range of

narrow gap semiconductor devices, where mercury cadmium

telluride (HgCdTe) and indium antimonide (InSb) are the most

common.

Cooled-detector Thermal Imaging Cameras


The highest possible thermal sensitivity.

Able to detect people and vehicles at great

distances.

Not affected by bright light sources.

Able to perform high speed infrared imaging.

Able to perform multi-spectral infrared imaging.

Expensive to purchase and to operate.

Limited cooler operating lifetime.

May require several minutes to cool down upon

initiation.

Bulky

Cooled-detector Infrared Cameras

Short-wave Infrared Cameras

Mid-wave Infrared Cameras

Long-wave Infrared Cameras

Multi-spectral Infrared Camera

Uncooled-detector Cameras

HOW THEY WORK: Unlike the cryogenically cooled detectors

described above, uncooled infrared detectors operate at or

near room temperature rather than being cooled to extremely

low temperatures by bulky and expensive cryogenic coolers.

When infrared radiation from night-time scenes are focused

onto uncooled detectors, the heat absorbed causes changes to

the electrical properties of the detector material. These

changes are then compared to baseline values and a thermal

image is created. Despite lower image quality than cooled

detectors, uncooled detector technology makes infrared

cameras smaller and less costly and opens many viable

commercial applications.

Uncooled detectors are mostly based on materials that change

their electrical properties due to pyroelectric (capacitive)

effects or microbolometer (resistive) effects.

Uncooled-detector Thermal Imaging Cameras


Relatively inexpensive compared to other thermal

imaging technologies.

High contrast in most night-time scenarios.

Easily detects people and vehicles.

Not affected by bright light sources .

Higher reliability than cooled detector thermal

imagers .

Less sensitive than cooled detector thermal

imagers.

Cannot be used for multispectral or high-speed

infrared applications .

Uncooled-detector Thermal Imaging Products:

Uncooled thermal imaging camera (fixed mount)

Uncooled thermal imaging camera (portable)

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Near Infrared Illumination

A popular and sometimes inexpensive method for performing

night vision is by near infrared illumination. In this method, a

device that is sensitive to invisible near infrared radiation is

used in conjunction with an infrared illuminator. The Sony

Night Shot camcorder popularized this method. Because of the

IR sensitivity of the camcorder's CCD detector and since Sony

installed an infrared light source in the camcorder, infrared

illumination was available to augment otherwise low-light

video scenes and produce reasonable image quality in low-

light situations.

The method of near-infrared illumination has been used in a

variety of night vision applications including perimeter

protection where, by integrating with video motion detection

and intelligent scene analysis devices, a reliable low-light

video security system can be developed.

IR Illumination

HOW THEY WORK: Several different near infrared illumination

devices are available today, including:

Filtered incandescent lamps: A standard high power lamp that

is covered by an infrared filter designed to pass the lamp's

near infrared radiation and block the visible light component.

These devices typically need good heat transfer properties

since the intense visible light is internally absorbed and

dissipated as heat.

LED type illuminators: These illuminators utilize an array of

standard infrared emitting LEDs.

Laser type: The most efficient infrared illuminator, these

devices are based on an infrared laser diode that emits near

infrared energy.

Near infrared illuminators are typically available in a range of

wavelengths (e.g. 730nm, 830nm, 920nm). Providing

supplemental infrared illumination of an appropriate

wavelength not only eliminates the variability of available

ambient light, but also allows the observer to illuminate only

specific areas of interest while eliminating shadows and

enhancing image contrast. The supplemental near infrared

lighting not only improves the quality of image intensifier

devices (which have both a visible and a near-infrared

response), but also permits the use of solid state cameras,

which also have the ability to convert near infrared images to

visible.

IR Illumination


Lowest cost compared to other night vision

technologies.

Eliminate shadows and reveal identifying lettering,

numbers and objects. Can also be used to perform

facial identification.

Able to perform high-speed video capture (such as

reading license plates of moving vehicles).

IR illuminators can see through night-time fog, mist,

rain and snowfall as well as windows.

Eliminates the variability of ambient light.

Users of infrared illuminators can be detected by

others that have near-infrared viewing devices.

IR Illumination Products:

Wide area infrared laser illuminator

Portable Laser illuminator

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