The target radiation can only reach through the air and be imaged on the infrared thermal imaging camera. In addition to attenuating the target's radiation, the air will also add some interference signals during the transmission process. In the infrared band, the atmosphere is transparent at some wavelengths and opaque or semi-transparent at other wavelengths. Therefore, the infrared radiation measured by a target at a close distance is different from the radiation emitted from the same target at a long distance.