Night vision instrument - eagle eye for the night
(1) Working mode
Night vision instruments can be divided into microwave night vision instruments and infrared night vision instruments according to the types of light they process. The former deals with natural light and the latter deals with infrared light.
The low light level night vision instrument can enhance and amplify a small amount of natural light (Moonlight, starlight, atmospheric glow) reflected by the target under dark conditions, so as to realize human observation and detection of objects and environment under low light level at night. Because the low light level night vision system works by using the night sky light, it works in a passive way, so it can better hide itself. It is very suitable for special work departments, such as military, criminal investigation, drug collection, private collection, night monitoring, security, etc.
Infrared night vision instruments are divided into "active infrared night vision instrument" and "passive infrared night vision instrument".
"Active infrared night vision" forms an image by receiving the infrared reflected by the target, which requires that active infrared night vision should have the function of emitting infrared. Although the emitted infrared beam is invisible to the human eye, there will still be a red dot in the emission section, which is easy to reveal the user's position. Therefore, active infrared night vision is more used for civil use.
"Passive infrared night vision instrument" relies on the infrared radiation of the target itself to form a "thermal image", so it is also called "thermal imager". Infrared ray can be divided into near infrared ray (near IR, with a wavelength range of 0.7-1.3 μ m, adjacent to visible light), medium infrared ray (medium IR, with a wavelength range of 1.3-3 μ m), and thermal infrared ray (thermal IR, with a wavelength range of 3-30 μ m). Near infrared and mid infrared are mainly reflected from objects and are mainly used in various electronic devices, such as remote controls and active infrared night vision devices. The thermal infrared ray is emitted from objects. The "passive infrared night vision instrument" observes the thermal infrared ray without additional power supply. Therefore, it has better concealment, is not easy to be found by the enemy and prey, and is more suitable for the military and police.
(2) Operating principle
Microwave night vision system and active infrared night vision system both use image enhancement technology to magnify the target image, also known as image intensifier tube night vision system. At present, the microwave night vision instruments we see in the market also have the function of active infrared night vision, and some manufacturers call them microwave infrared night vision instruments.
The low light level night vision instrument consists of four main components: strong light force objective lens, image intensifier, eyepiece and power supply. In terms of optical principle, low light level night vision system is a special telescope with image intensifier. The image intensifier is used to collect and amplify infrared and visible light, and the process of converting light into electricity and then into light is used to realize image amplification. Weak natural light and infrared ray are reflected from the target surface and enter the night vision instrument through the objective lens; Under the strong light force of the objective lens, the light focuses on the image intensifier and excites photoelectrons; The photoelectron is accelerated, focused and imaged under the action of the internal electronic optical system of the image intensifier, and bombards the connected fluorescent screen at a very high speed. Finally, it excites enough visible light to turn a remote target under weak natural light conditions into a visible light image suitable for human observation and present it in the eyepiece.
According to the image intensifier technology, the LLL night vision system can be divided into the first generation, the second generation and the third generation.
The first generation low light level night vision instrument uses cathode vacuum tube as photoelectric coupling multiplier and cascade image intensifier. The image enhancement magnification is about 120-900 times. Most of the first generation products can only clearly observe the central area, while the image resolution at the boundary is low and the image is distorted. At the same time, when the first generation night vision instrument suddenly appears a bright light source within the observation field of vision, the equipment may be burned, so it is strictly prohibited to use the first generation product in a strong light environment. Generation plus is an improvement from the first generation. It corrects the image distortion formed by photoelectric coupling elements and improves the resolution by adding optical lens components, so as to reduce the image distortion and enhance the magnification by about 1000 times. The technology of accelerating electronics adopted by the first generation and the first generation of enhanced night vision instruments has obviously led to the reduction of image quality and the shortening of the life of picture tubes.
The second generation low light level night vision instrument uses an image intensifier with a microchannel plate. Photons enter the night vision instrument and hit the metal plate to convert photons into electrons. These electrons pass through a thin disk called microchannel plate placed in front of the light screen. There are millions of microchannels on the disk. After entering the microchannel, the electrons are multiplied by high pressure. Therefore, the image distortion of the LLL night vision instrument is significantly reduced, with high spatial resolution and good image visibility. At the same time, it also has the characteristics of automatic anti glare performance and long observation distance, and its service life is also extended.
The outstanding mark of the third generation LLL night vision instrument is the image intensifier with a very sensitive GaAs photocathode coating. Its image is clearer and its service life is longer, but its process is complex and its cost is expensive. Even in developed countries, only a few models have been successfully developed. During the transition from the second generation to the third generation, a super second generation photocell called the second generation plus has been developed, and its technical performance is second only to that of the third generation products.
At present, the highest night vision instruments seen in the Chinese market are the second-generation plus products. The third-generation products are generally military products of the United States. Their sales in the international market need to obtain an export license from the U.S. State Department, and the prices have reached more than 100000 yuan.
(3) Performance parameter index
The most important parameter of night vision instrument is the observation distance. The observation distance of low light level night vision instrument is mainly affected by its image intensifier algebra. Specifically, it is divided into low light level observation distance and all black observation distance. Measuring the quality of low light level night vision instrument mainly depends on the observation distance under low light level.
The low light level observation distance is generally based on the sunny weather and the 1/4 full moon. Generally, the low light level observation distance of the first generation or the first generation plus night vision instrument is 50 to 100 meters; The second and third generation night vision instruments have a low light level observation distance of about 400 meters in 100 cities. If the environment is bad or the light is weaker, the low light level observation distance will be closer. At present, the low light level night vision instruments with tens of thousands of yuan on the market can not observe at a distance of more than 400 meters under low light level. Generally, the low light level observation distance of a night vision instrument of about 1000 to 3000 yuan is about 50 meters.
In addition to the quality of night vision image intensifier, the total black observation distance is also the main factor. At present, the distance of infrared emission lamp equipped with night vision instrument is generally about 50 meters. That is to say, no matter how expensive the night vision instrument is, it can observe up to 50 meters away in the case of all darkness.
2 thermal imaging night vision instrument
(1) Operating principle
All objects whose temperature is above the absolute zero of thermodynamics emit electromagnetic radiation by themselves, while the radiation peak corresponding to the temperature of general natural objects is in the infrared band. The infrared thermal imager uses the infrared detector and optical imaging objective lens to reflect the infrared radiation energy distribution pattern of the measured target to the photosensitive element of the infrared detector, so as to obtain the infrared thermal image, which corresponds to the thermal distribution field on the object surface. Generally speaking, the infrared thermal imager is to convert the invisible infrared energy emitted by an object into a visible thermal image. The different colors on the thermal image represent the different temperatures of the measured object. At the same time, by detecting the emission and absorption of infrared radiation, it can be used to analyze the state, structure and state of substances. The thermal imaging night vision system can observe the target exactly the same in all dark and daytime, and is not affected by light.
(2) Performance parameter index
Detector resolution: one of the most important indicators of the thermal imaging night vision instrument is the detector resolution, generally 160*120336*256384x288640*480.
Resolution of built-in screen: the low light level night vision instrument directly observes the target through the lens, so the field of vision is the same as the telescope. The thermal imaging night vision device observes the target by observing its internal LCD screen. What our eyes see is the image on the internal LCD screen, rather than directly seeing the target. Therefore, the clarity of the thermal imaging night vision device depends on the built-in LCD screen. Generally, the built-in screens are color LCOS screens or LED screens, and the OLED 800x600 ultra clear LCD screen is the top built-in LCD screen.
Single and dual barrel: dual barrel is significantly better than single barrel in terms of comfort and observation effect. Of course, the price of dual barrel thermal imaging night vision instrument will also be much higher than that of single barrel thermal imaging night vision instrument.
Magnification: the night vision instrument can shorten the distance, shorten and enlarge the observed target. Generally, the magnification of the thermal imager is 2 or 4 times.
Objective lens aperture: generally, the objective lens aperture of night vision instruments on the market is between 14~75mm. The viewing effect and field of view of large lens are much better than that of small lens. The price of night vision instruments also varies greatly due to different objective lens aperture.
Frame rate: frame rate refers to the number of frames or images projected or displayed on the built-in screen per second. The higher the frame rate, the faster the animation will be. Too low frame rate will cause intermittent playback.
3 main differences between low light level night vision system and infrared thermal imaging night vision system
(1) The infrared thermal imaging night vision system has obvious advantages under the conditions of full darkness, harsh environment and large changes in light intensity
The infrared thermal imaging night vision device is not affected by visible light, so the observation distance of the infrared thermal imaging night vision device under all black and ordinary light is exactly the same, and it is not affected by fog, rain and other adverse environments. However, the LLL night vision system must rely on the auxiliary infrared light source when it is completely dark, and the distance of the auxiliary infrared light source can only reach 50 meters. The observation distance of traditional night vision instruments will be greatly reduced. However, the infrared thermal imaging night vision system will be little affected. At the same time, the low light level night vision device should not be used in the daytime. Strong light will damage the device components. It is also for this reason that the top vehicle night vision devices, such as those used in Mercedes Benz and BMW, all use thermal imagers.
(2) Low light level night vision system has advantages over infrared thermal imaging night vision system in the recognition of target details
Infrared thermal imaging night vision system can identify the category of the target by the shape and color of the target, and distinguish whether the target is human or animal. The low light level night vision instrument observes the target through the principle of image enhancement, and can clearly see the five features of the character when the definition is enough. At the end of 2015, a video of the U.S. military bombing the is army was widely circulated on the Internet, and more attention was paid to the infrared thermal imaging technology used by the U.S. military in this battle. Under the night vision lens, we can observe the environment around is armed forces and even the action track of military targets. It is reported that "is pickups are running around like white mice on the ground, and is armed personnel on the ground are as panicked and rash as white ants. The bright white is armed personnel and vehicles form a sharp contrast with the black background. "