NIGHT VISION TECHNOLOGY(NVT)

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NIGHT VISION TECHNOLOGY(NVT):

NIGHT VISION TECHNOLOGY(NVT) MD.SALMAN.AHMED III YEAR E.C.E P.C.E.T NELLORE T.SRINADH III YEAR,E.C.E A.S.C.E.T GUDUR

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INTRODUCTION Night vision technology is a type of image processing where we get to see Images in the dark. With the proper night vision equipment you can see a person standing over 200 yards(183mtr) away on a moonless cloudy night. Night vision can work in two different ways depending on technology used. They are.. Thermal Image Image enhancement

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Basics of light The amount of energy in a light wave is related to its wavelength. Shorter wavelengths have higher energy. In visible light,violet has the most energy and red has the least. Infrared light is a small part of the light spectrum. Infrared light spectrum which 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 .

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THERMAL IMAGING

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A special lens focuses the infrared light emitted by all the objects in view. The focused light is scanned by a phased array of infrared-detector elements. The detector elements create a very detailed temperature pattern called a thermo-gram. The thermo gram created by the detector elements is translated into electric impulses, these impulses are sent to a signal processing unit. These signal processing unit sends the information to the display, where it appears as various colors depending on the intensity of the IR-emission. Finally, the combination of all the impulses from all of the elements creates the image.

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The first image shows when it was taken in darkness . The second image shows after using thermal image technique. Image devices scan at a rate of 30 times per sec. They can sense temp ranging from 20 deg C-2000 C. Two common types of thermal imaging devices are: Un-cooled Cryogenically cooled

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IMAGE ENHANCEMENT

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Image enhancement systems are normally called night vision devices.these devices relys on a special tube called an image intencifier tube,to collect and amplify infrared and visible light. A conventional lens called objective lense captures ambient light and some near IR- light.The gathered light is sent to the image intencifier tube. The image intencifier tube has a photo cathode which is used to convert the photons of light energy into electrons. Electrons pass to the tube simmilar electrons are released from atoms in the tube,multyplying the original num of electrons by a factor of thousands through the use of a micro channel plate(MCP). MCP is a tiny,glass disc that has millions of microsccopic holes in it,and it is made by using fiber optic technology.

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Each channel is about 45 times longer than it is wide, and it works as a electron multiplier. As electrons pass through micro channels they cause thousands of other electrons to be released in each channel using a process called cascaded secondary emission. At the end of image intensifier tube the electron hit a screen coated with phosphors, these phosphorus create a green image on the screen that has come to characterized night vision. The green phosphor image is viewed through another lens called ocular lens, which allows you to magnify and focus the image.

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GENERATIONS OF NVT There are four generations in NVT. They are… Generation 0; The original night vision system created by the united states army and used in world war ii and the Korean war, these nvt are active IR. This means that a projection unit called an IR illuminator is attached to the nvt. The problem with this approach is that the acceleration of the electron distorts the image and greatly decrease the life of the tube. Another problem with this technology is in its original military use was that it was quickly duplicated by hostile nations which allowed enemy soldiers to use their own nvt’s.

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Generation 1: The next generation of nvt”s moved away from active IR,using passive IR. These nvt”s use ambient light provided by the moon and stars to augment the normal amounts of reflected IR in the environment. This means that they do not work very well on cloudy or moonless nights. Gen 1 nvt”s use the same image intensifier tube technology as gen 0,so still a problem.

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Generation 2: Major improvements in image intensifier tubes resulted in gen 2. They offer improved resolution and performance over gen 1 devices. The gain in gen 2 is the ability to see in extremely low light condition, such as moonless night. This increased sensitivity is due to addition of MCP to the image intensifier tubes.

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Generation 3: It is the latest nvt technology ,it is currently used by U.S.A military. Here MCP is coated with an ion barrier, which dramatically increases the life of the tube. These nvt”s have batter resolution and sensitivity compare to gen 2,this is because the photo cathode is made using gallium arsenide, which is efficient in converting photons to electrons. Gen 3 nvt”s are considered as state-of-the-art they cannot be exported from U.S without a license from U.S. department.

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APPLICATIONS Common applications for night vision include: Military Navigation Surveillance Law enforcement

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conclusion

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