2023-06-29 14:34:18

Fog Penetration of SWIR Camera

Visible imaging systems are often affected by atmospheric environments, such as fog and haze. Why is visible light subject to this constraint? The atmospheric transmittance curve shown in Figure 1 is a globally recognized measurement result. It can be seen from the figure that at a distance of 1.8km, with 17mm of water vapor, the atmospheric transmittance in the 0.4~1.3um band can reach 70%. This indicates that visible light can 'penetrate fog'.

Figure 1 Atmospheric transmittance at a distance of 1.8km

Let's start with the imaging principle of visible light: objects themselves do not emit light, they are imaged by reflecting sunlight. Reflected light is transmitted through the atmosphere, absorbed and scattered by particles in the atmosphere (300-800nm light can reach the ground through the atmosphere, including what we call visible light). Although visible light is not absorbed during transmission, there may be scattering phenomena. According to the Rayleigh scattering law, the intensity of Rayleigh scattering is inversely proportional to the fourth power of the wavelength, indicating that the dispersion of short wave light is greater than that of long wave light. So the atmospheric phenomenon of haze that we can see is due to light scattering.
The imaging principle of shortwave infrared is similar to that of visible light, and the wavelength of shortwave infrared is longer than that of visible light, making it less prone to scattering and thus achieving fog penetration. And shortwave infrared is different from medium wave infrared and long wave infrared. The imaging of shortwave infrared is more like visible light than thermal imaging. In contrast, the transparent fog of shortwave infrared is more suitable for our human visual characteristics, and can effectively observe target characteristics in foggy weather observation, highway monitoring, and sea surface detection.

The above shortwave infrared imaging images were all taken by the Gatherstar GS-SW6401715-C camera.

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Xi'an Gatherstar Optoelectronic System Co.,Ltd is specialized in infrared and laser photoelectric system products and module, components and elements. we are not only confident in supplying qualified optoelectronic products to all of our customers, but also concentrating on offering continuous innovations and reliable service.