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ABSTRACT
This paper describes the various Night vision techniques. “Night Vision" is referenced as 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 described here are Low-Light Imaging, Thermal Imaging and Illumination’s. This paper also give brief idea about various night vision device (NVD) that allows images to be produced in levels of light approaching total darkness, it also explains various applications where night vision technology is used to solve various problems due to low light conditions .
This system, implemented mainly by adopting infrared cameras and computer vision techniques, aims at enhancing safety and convenience of night driving by providing functionalities such as adaptive night vision, road sign detection and recognition, scene zooming and spotlight projection. We have tested the system in both simulated laboratory environments and in field highway environments. Initial results show the feasibility of constructing such a system.
1. INTRODUCTION
In fall 200, BMW introduced Night Vision on series – 7.This system processes far infrared radiation, which minimizes non-essential information placing a greater emphasis on pedestrian and animal, allows for a range of 300 meters or nearly 1,000 feet, and avoids “dazzle” from headlights, road lights and similar intense light sources. In fall of 2008, on the redesigned 7-series, BMW added a pedestrian detection system which flashes a caution symbol on navigation / information screen and head up display when it detects a pedestrian. The objective of the pedestrian warning algorithms is to accurately detect pedestrian and provide the driver with informative warning. In eyes of the driver, the end product of the good system provides the timely warning and possibly, additional information such as the position of the pedestrian or an overlaid on the night vision display. There are two different technologies in the market for night vision system. Far infrared (FIR) also called passive infrared And Near infrared (NIR) also called active infrared.
1. Night Vision System
The Bmw night vision system provides the driver with the black and white image of the driving environment ahead of the vehicle in the central information display (CID).BMW night vision is 100% passive system without active infrared illumination. Objects situated ahead of the vehicle are shown in varying degrees of the brightness depending upon the temp of these objects. This enables the driver to detect in good time heat emitting objects such as peoples. Animals and the other vehicles.
2. Use of the Night vision system in cars
This thermal image is recorded with a far Infrared camera (FIR) via a special imaging sensor which detects the infrared radiations in a specific wavelength range. The BMW system is distinguish from infrared system with active illumination by its long range, and its clearly structured image. Infrared energy coming from an object is focused by the optics onto an infrared detector. A thermal imaging camera can produce a comprehensive image on which the smallest of the temperature difference can be seen. Contrary to other technologies, such as e.g. light amplification, that at least small amount of light to generate an image, thermal imaging needs no light at all.
Improve vision in twilight and darkness and the display does not dazzle by the head lights of the oncoming vehicles. Pronounced highlighting of process, animals and warm objects as well greater overview of driving situation due to display of course of road beyond that illuminated by headlights. It gives magnified image of the distant objects when driving fast through zoom function improved recognisation of objects on bends in the road through horizontally adjustable image section. It enhances personal safety of dark ways and garage entrance through display of living creature.
A far infrared camera in the grill, just over an inch in diameter, senses the temperature of everything in front of the vehicles. A computer then converts the data into an image that appears on the navigation display unit into the dashboard. Warmer objects (a pedestrians, an animal) appears white; cooler objects (parked cars, detritus) appears black. When the car exceeds 25 mph, the system scans specifically for pedestrians by scanning the road up to 100 yards ahead of the vehicle. A pedestrian appears with the yellow tint.
Practically, drivers may experience more difficulties in identifying these objects during the night driving, leading to a much higher probability of traffic accident. Statistics shows that in US, more than 20% of fatal traffic accidents occurred between midnight and 6:00 in the morning, which accounts for only 2.4% of total traffic volume. Besides the drivers’ lacking of attention, largely reduced visual acuity and field of vision at night due to low illumination caused by factors such bad weathers, obscure street lamps and limited range of headlights is also a major reason for this situation. For example, dipped headlights only illuminate about 56 meters when the breaking distance at 100 km/h is about 80 meters.
NIGHT VISION TECHNOLOGY
1: Image intensification
2: Active illumination
3: Thermal imaging
1. Image Intensification System
Image intensification systems support direct observations by amplifying low levels of available light. They do not ‘turn night into day’ Nor do they overcomes the problems that affect vision in low light environments. The image intensifier is a vacuum-tube based device that converts invisible light from an image to visible light so that a objects in the dark can be viewed by a camera or the naked eye. When light strikes a charged photocathode plate, electrons are emitted through a vacuum tube that strike the micro channel plate that cause the image screen to illuminate with a picture in the same pattern as the light that strikes the photocathode, This is much like a CRT television, but instead of colour guns the photocathode does the emitting. The intensified image is, typically, viewed on a phosphor screen that creates a monochrome, video-like image, on the user’s eyepieces.
Fig 2: Image intensification systems
2. Active Illumination
Active illumination technologies work on the principle of coupling imaging active
Illumination in the near infrared (NIR) band. Infrared is used in night vision technology when there is insufficient visible light to see, active illumination involves conversion of ambient light photons into electrons which are then amplified by a chemical and electrical process and then converted back into visible light. Active infrared night vision combines infrared illumination in spectral range 0.7–1 μm. Due to which The scene, which appears dark to a human observer now appears as a monochrome image on a normal display device. Since active infrared night vision systems can incorporate illuminators that produce high levels of infrared light, the resulting images are typically higher resolution than other night vision technologies.
The use of infrared light and night vision devices should not be confused with thermal imaging which creates images based on differences in surface temperature by detecting infrared radiation (heat) that emanates from objects and their surrounding environment.
3. Thermal Imaging
In order to understand thermal imaging, it is important to understand something about light. The amount of energy in a light wave is related to 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.
Fig 3: spectrum of light
Infrared light can be split into three categories:
1. 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.
2. 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.
3. Thermal-infrared (thermal-IR) - Occupying the largest part of the infrared spectrum, thermal-IR has wavelength ranging from 3 microns to over 30 microns.
Working Of Thermal Imaging
A special lens focuses the infrared light emitted by all of the objects in view. The focused light is scanned by a phased array of infrared-detector elements. The detector elements create a very detailed temperature pattern called a thermo gram. It only takes about one-thirtieth of a second for the detector array to obtain the temperature information to make the thermo gram. This information is obtained from several thousand points in the field of view of the detector array. The thermo gram created by the detector elements are translated into electric impulses.
The impulses are sent to a signal-processing unit, a circuit board with a dedicated chip that translates the information from the elements into data for the display. The signal-processing unit sends the information to the display, where it appears as various colors depending on the intensity of the infrared emission. The combination of all the impulses from all of the elements creates the image.
Fig 4: Thermal imaging system
There are two common types of thermal-imaging devices:
i) 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.
ii) 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).