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1. What Is Infrared Radiation
In nature, all objects whose temperature is higher than absolute zero (-273.15 ° C) can radiate infrared energy. The physical essence of infrared radiation is thermal radiation, which is also an electromagnetic wave.
Infrared ray is a kind of light invisible to the naked eye, which was discovered by British astronomer William Herschel in 1800, also known as infrared thermal radiation.红外辐射本质是一种电磁辐射，在物理学上定义波长在0.75~1000μm的电磁波。
2. Wavelength Classification Of Infrared Radiation
The wavelength of infrared radiation is between visible light and microwave, its short wave is adjacent to the red light in visible light band, and its long wave band is connected with microwave.
According to the generation mechanism of infrared radiation, the application and development of infrared radiation, and considering the transmission characteristics of infrared radiation in the earth's atmosphere, it is further reduced to 0.75~1000 μ The infrared radiation of M is divided into four bands:
（1）Near Infrared, NIR : 0.75~1 μm
(2) Short wave infrared, with wavelength range of 1~3 μm；
(3) Medium infrared or medium wave infrared, with a wavelength range of 3~5 μm;
(4) Far infrared or long wave infrared, with a wavelength range of 7.5~14 μm；
3. Infrared Atmospheric Window
Infrared detectors use infrared radiation for imaging. Based on the "atmospheric window" of infrared transmission in the atmosphere, the application of infrared is divided intoshortwave infrared、medium wave infraredandlong wave infraredthree categories. Short wave infrared uses the short wave infrared radiation that is common in the target reflection environment, which is similar to the visible light image in resolution and detail; Long wave and medium wave infrared imaging uses the thermal radiation emitted by the target itself at room temperature for various infrared thermovision devices.
When infrared ray is in the atmosphere or penetrates the atmosphere, it will be affected by the radiation transmission from the atmosphere, resulting in the attenuation of the ability of light, which is also called atmospheric extinction. The influence of atmospheric extinction on infrared radiation is related to wavelength and has obvious selectivity.Infrared has high transmittance in three bands in the atmosphere, which is called "atmospheric window",respectively: 1~3 of short wave infrared region μ M-band, mid infrared region 3~5 μm-band and far infrared region 8~14 μm。
4. Characteristics Of Infrared Imaging
Infrared thermal imager uses photoelectric technology to passively detect the infrared radiation emitted by the object, calculate the temperature of each point on the surface of the object, and display different temperatures in different colors, so as to convert it into images and graphics that can be distinguished by human vision. Infrared thermal imager can break through the barrier of human vision, detect objects in a completely dark environment, even in the case of smoke and dust, and does not need light source illumination, so it can be used all day.Because infrared thermal imaging has the characteristics of good concealment, strong anti-interference, strong target recognition ability, all-weather work and so on, it plays an increasingly important role in military and civil fields.
