Night Vision Technologies: Types, Characteristics, Operating Principles & Applications
Night vision signifies the ability to see in dark in night. This capability is normally possessed the by owls and cats, but with the development of science and technology devices has been develop which can enables human being to the see in dark night as well an in adverse atmospheric conditions such as the fog, rain, dust etc. The muscles in the human eye have the ability to the stretch or contract automatically, depending upon the intensity of the light falling on the eye. When we go for out in bright sunlight, the pupil gets contracted. Alternatively, when we enter the shaded or dark room at that time the muscles of the eye relax and make the aperture of the eye lens big enough to the allow sufficient amount of the light to pass through, therefore the objects in the room appear are blurred. Because of this human eye have the limitations. The muscles of the eye cannot be increase the aperture indefinitely.
Therefore, in poor night light we are unable to see the objects because of the image cannot be formed on the retina clearly. The capability to be detect and identify targets at the night and under the poor visibility conditions has been the essential military requirement. The modern army’s need to be operate at night and the under conditions of extremely poor visibility, Since the soldiers have to often fight in the dark at the night, they have to face a severe stress as far as the location of the target is concerned. Also various type wild life observer have to face problems of the low light because many wild animals are the more active during night time than day, therefore to the observe there lifestyle and study it night vision is the important. Therefore to be make human being unable to see in dark by technological means, night vision technology has been the developed. This paper describes various techniques and different devices are developed to enable viewing in dark night.
Types of Night Vision Technologies
- Image intensification
- Active illumination
- Thermal imaging
Image intensification systems support direct observations by the amplifying low levels of the available light. They do not ‘Turn night into day’ Nor do they overcomes the problems that effect on vision in low light environments. The image intensifier is a vacuum tube based device that converts into invisible light from the image to visible light so that an objects in the dark can be viewed by the camera or the naked eye. When light strikes a charged photocathode plate, electrons are the emitted through a vacuum tube that strike the micro channel plate that cause the image screen to be illuminate with a picture in the same pattern as the light that strikes the photocathode, This is a much like a CRT television, but instead of the colour guns the photocathode does the emitting. The intensified image is typically viewed on a phosphor screen that creates the monochrome, video like image, on the user’s eyepieces.
- Excellent low night light level sensitivity.
- Enhanced visible imaging yields the best possible. Recognition and the identification of the performance.
- The High resolution.
- Low power and the cost.
- Ability to be identify people.
- Because they are the based on the amplification methods, some light is required. This method is not useful when there is the essentially no light.
- Inferior daytime performance when compared to the daylight only methods.
- Possibility of the blooming and the damage when observing bright sources under low light conditions.
Active illumination technologies are work on the principle of the coupling imaging intensification with an active source of the illumination in the near infrared (NIR) band. Infrared is the used in night vision technology when there is insufficient visible light to see, active illumination involves the conversion of ambient light photons into electrons which are the amplified by a chemical and the electrical process and then converted back into visible light. Active infrared night vision combines infrared illumination in the spectral range 0.7–1 μm.
Due to the scene, which appears dark to a human observer now appears as the monochrome image on a normal display device. Since active infrared night vision systems can be incorporate illuminators that produce high levels of the infrared light, the resulting images are typically higher resolution than other night vision technologies. The use of the infrared light and night vision devices should not be the confused with thermal imaging which creates images based on the differences in surface temperature by detecting infrared radiation that emanates from the objects and their surrounding environment.
In the order to understand thermal imaging, it is the important to understand something about light. The amount of the energy in a light wave is related to its wavelength. Shorter wave lengths have the higher energy of visible light, violet has the most energy, and red has the least. Just next to the visible night light spectrum is the infrared spectrum.
A special lens focuses on the infrared light emitted by all of the objects in view. The focused light is scanned by a phased array of the infrared detector elements. The detector elements create a very detailed temperature pattern called as thermo gram. It is only takes about one-thirtieth of a second for the detector array to the obtain the temperature information to make the thermo gram. This information is the obtained from several thousand points in the field of the view detector array. The thermo gram created by the detector elements are the translated into electric impulses.
The impulses are sent to the signal processing unit, a circuit board with a dedicated chip that translates the information from the elements into data for the display. The signal processing unit sends the information to the display, where it is appears as the various colours depending on the intensity of the infrared emission. The combination of the all the impulses from all of the elements creates the image.
Applications for night vision technologies
Common applications for the night vision include
- Application for Military
- Application for Law enforcement
- Application for Hunting
- Application for Wildlife observation
- Application for Surveillance
- Application for Security
- Application for Navigation
- Application for Hidden object detection
- Application for Entertainment
Technical characteristics of night vision
Using intensified night light vision is different from using regular binoculars and & or your own eyes. Below are the some of the aspects of night vision that you should be aware of the when you are using an image intensified night vision system.
1.Textures, Light and Dark
Objects that appear light during the day but have the dull surface may appear darker through the night vision unit than objects that are the dark during the day but have a highly reflective of the surface. For example, a shiny, dark colour jacket may appear brighter than the light coloured jacket with the dull surface.
Night light vision does not present the normal depth perception.
3.Fog and Rain
Night vision is the very responsive to reflective ambient light; therefore, the light reflecting off of fog or heavy rain causes much more the light to go toward the night vision unit and may be degrade its performance. However advances in the latest night vision technologies help to offset these effects.
Honeycomb is the faint hexagonal pattern, which is the result of the manufacturing of the process.
A few black spots throughout the image area also are the inherent characteristics of all night vision technology. These spots will not be increase in size or the number. Do not be concerned if you they see this feature. It is an inherent characteristic found in the light amplification night vision systems that can be incorporate a micro channel plate in the intensifier.
Loss of the entire night vision image, parts of it, or small parts of it, due to the intensifier tube overloading by the bright light source. Also, known as the “halo” effect, when the viewer sees a “halo” effect around the visible light sources. When such a bright light source comes into the night vision device’s view, the entire night vision scene, or parts of it, becomes a much brighter, “whiting out” objects within the field of the view. Blooming is the common in Generation 0 and 1 devices. The night lights in the image to the right would be as considered to be “blooming”.
7.Bright-Source Protection (BSP)
High Light Cut Off, an electronic function that reduces the voltage to the photocathode when the night vision device is the exposed to bright light sources such as the room lights or carlights.BSP protects the image tube from damage and enhances its life; however, it also has the effect of the lowering resolution when functioning.
Types of ranges
Spectral range approaches that are the useful at night can be detect radiation that is undetectable to the naked eye. Visible light is a small fraction of the electromagnetic spectrum that humans can be seen. The viewer can be take advantage of the non-visible sources of the electromagnetic radiation because of the increased spectral range such as near infrared or ultraviolet radiation. Some creatures, such as the mantis shrimp and trout, can be see infrared and ultraviolet light in the far greater amounts than humans.
The ability to see with very small amounts of the light is referred to as sufficient intensity range. Because of the variations in the morphology and anatomy of their eyes, many animals have greater night vision than the humans. These include the larger eyeball, a larger lens, a greater optical aperture the pupils may be extend to the physical limit of the eyelids, a acetum lucid, and the more rods than cones in the retina. The employment of an image intensifier, gain multiplication CCD, or other very low noise and the high sensitivity arrays of photo detectors is used to be increase the intensity range.
I2 devices use components known as the photomultiplier tubes to enable visibility in very low light scenarios. The overall operating principle for the Gen 2 and 3 photomultiplier tubes is the illustrated in Figure. The photomultiplier tubes are use a lens to collect available light, including light from the infrared portion of the spectrum. Once past the lens, the light strikes the photocathode which causes the release of the electron.
The electrons travel through the tube, accelerating towards another plate and causing a cascade effect that increases the number of the electrons. These electrons strike a screen coated with a phosphorescent compound that will be glow as shown in Figure. When the using an I2 NVD, the operator views the scene through an ocular lens that focuses on the image. The separation between the ocular lens and the eye, known as the eye relief distance, is necessary. Many types of the phosphor screens are available on I2 devices, with the most common being designated P22 green, P43 yellow & green, and P45 white.
The P22 screen is the most of the commonly used, and is the popular choice for the military and law enforcement due to the wider visible spectrum. The P43 screen has the narrower visible spectrum and has become the popular among aviators for its fast decay time i.e. the time it takes for the image to fade on the screen. The P45 screen are provides similar decay times to P43, with the excellent recognition capability. The image presented to the user of a P45 screen is black and white, which results in the less eye fatigue, faster recognition especially in sandy/rocky terrain, and a slightly better discrimination of the shades of the intensity than the traditional green.
Various night vision innovations that are the accessible and in addition its research with a common end goal to be avoid various low light problems, this paper shows how efficiently an officer can be act in the middle of the night additionally untamed life eyewitness can be operate in the middle of the dull and also shows how to observation can be held in the low light. The oldest electro optical surveillance technology is the night vision based on light intensifier tube technology. How this old nature technology is still in a phase of the development, despite heavy competition from the thermal imagers, visible / NIR cameras and the digital night vision.
Night vision is the completely developed technology with applications and mass in the defence. Security and defence sectors. One of the international market NVDs are the provided in the form of a long series of the devices with different design configurations, type of the image intensifier tube, type of the night vision optics, and performance. The Night Vision System (NVD) is without doubt one of the auto industry’s most of the enduring apps. A phased array of infrared detector components scans the focussed light. The elements of the detector generate the very complex temp pattern called as thermo gram.