Fog-penetrating camera is used for high-altitude viewing monitoring

In recent years, the rapid development of cities has brought a series of environmental pollution, such as automobile exhaust, industrial emissions, construction dust, garbage incineration, etc. These pollution sources are mixed to form "smog weather". In hazy weather, the color of the images monitored by most video surveillance systems will be dim and the contrast will be lower, so the details of some important objects will be submerged in the fog and difficult to find, which will lead to the normal video surveillance system. Functionality is affected. Although the smog is so serious, you may not be able to find your way home when you walk in the freezing cold wind, but why is the traffic system still generating revenue? This question puzzles many drivers. In fact, the principle is to use With the fog-penetrating camera, the general high-altitude observation monitoring is equipped with a fog-penetrating camera, so even in the case of heavy fog, it can still work with a high degree of clarity. So what is the principle of the fog-penetrating camera? Let’s analyze it below. . 1. The fog-penetrating principle of fog-penetrating camera Natural light is composed of light waves with different wavelengths. The visible range of the human eye is roughly 390nm-780nm. The wavelengths from long to short correspond to seven colors of red, orange, blue, green, green, orange, and purple. Among them, the wavelengths less than 390nm are called ultraviolet rays, and those with wavelengths greater than 780nm are called ultraviolet rays. called infrared. The small particles in the air such as fog and smoke block the light, so that the light cannot be reflected and cannot pass through. Therefore, the human eye who can only receive visible light cannot see the objects behind the smoke and fog. The longer the wavelength, the stronger the diffraction ability, that is, the stronger the ability to bypass the barrier, while the infrared rays are less affected by aerosols during propagation because of their longer wavelengths, and can pass through a certain concentration of fog and dust to achieve accurate focusing. , which is the basis for optical fog penetration. Three elements to achieve fog penetration: In the range of invisible light, light of a certain frequency can penetrate the fog, but due to the different wavelengths, it needs to be processed on the camera to achieve the purpose of focusing it, and it also needs to be redesigned on the camera to be used. The invisible light of this frequency is imaged. Since this invisible light has no corresponding visible light color map, the image presented on the monitor is black and white. (1) Lenses with chromatic aberration compensation In order to get a better fog penetration effect, the design of the lens is very important. In order to ensure that ideal images can be obtained before and after the visible light imaging system is fogged, the lens must ensure high transmittance in the visible light and near-infrared bands, and the chromatic aberration is corrected during the switching of the two bands to ensure that there is no need for further switching after switching. Adjust the focus. The central wavelength of the transmission spectrum of ordinary lenses is between 500 and 600 m, and the lens in the fog-transmitting system needs to have high transmittance at 500 to 600 nm and 780 to 900 nm. The transmittance of the lens in the 500-900 nm band is all greater than 80%. In principle, the wider the available near-infrared band, the better, but limited by the difficulty of the optical path design of the lens and the photosensitive ability of the CCD, the longest infrared band known to be used by the lens in the security industry is 1100nm. (2) CCD with high near-infrared sensitivity Ultra-high-sensitivity CCD cameras with good frequency response curves from the visible light band to the near-infrared band are a necessary condition for an excellent system, so that only one camera can be used, and the visible light band and the near-red band can be achieved by changing the filter. They are used separately for the purpose of improving the clarity of the image with the visible light band and increasing the viewing distance with the ability to penetrate the mist in the near-infrared band. (3) Image processing of black level stretching The scattering of water vapor and solid particles over oceans and cities results in flat, dark and white colors in the visible distance. Long-distance imaging cannot exceed the visible distance. The use of filters undoubtedly plays a big role, but it is necessary to To meet people's requirements for the clearer and better the long-distance observation image, and the farther the distance, the better. Electronic processing technology must be used to further filter out the gray-white film-like interference signal caused by scattering, and then process the useful white light or black and white signal to obtain excellent image signals of distant objects.