I. What is Infrared Radiation? All objects in nature with a temperature above absolute zero (-273.15°C) emit infrared energy. The physical nature of infrared radiation is electromagnetic radiation, meaning it is a form of electromagnetic wave. Infrared light is invisible to the human eye. It was discovered in 1800 by the British astronomer William Herschel, and is also known as infrared thermal radiation. In physics, infrared radiation is defined as electromagnetic waves with wavelengths ranging from 0.75 to 1000 micrometers (μm).

II. Wavelength Classification of Infrared Radiation The wavelength of infrared radiation lies between visible light and microwaves: its short-wave band is adjacent to red light in the visible spectrum, while its long-wave band connects with microwaves. Based on generation mechanism, applications and atmospheric transmission characteristics, infrared radiation can be divided into four bands: Band Categories: 1. Near-Infrared (NIR) Wavelength range: 0.75~1 μm Characteristics: adjacent to visible light 2. Short-Wave Infrared (SWIR) Wavelength range: 1~3 μm Characteristics: high-reflection imaging 3. Mid-Wave Infrared (MWIR) Wavelength range: 3~5 μm Characteristics: thermal radiation detection 4. Long-Wave Infrared (LWIR) Wavelength range: 7.5~14 μm Characteristics: imaging of room-temperature objects

III. Infrared Atmospheric Windows Infrared detectors form images using infrared radiation, and fall into three major categories based on the "atmospheric windows" in atmospheric transmission: - Short-wave infrared (SWIR): Relies on ambient reflected radiation, producing images similar to visible light. - Mid-wave / Long-wave infrared (MWIR / LWIR): Utilizes the thermal radiation of the target itself, used in thermal imaging equipment. When infrared radiation travels within or penetrates the atmosphere, its transmission is affected by atmospheric interference, resulting in optical energy attenuation — a phenomenon known as atmospheric extinction. The influence of atmospheric extinction on infrared radiation is wavelength-dependent and highly selective. Infrared radiation exhibits extremely high transmittance in three specific atmospheric bands, referred to as the atmospheric windows: - Short-wave infrared: 1–3 μm - Mid-wave infrared: 3–5 μm - Far infrared: 8–14 μm

IV. Infrared Thermal Imaging Technology Infrared thermal imagers are based on optoelectronic technology. By passively receiving infrared radiation emitted by objects, they accurately measure the temperature distribution across an object’s surface and visually display temperature differences in various colors, ultimately converting the data into images and graphics distinguishable by human vision. This technology breaks through the visual limitations of the human eye and has the following core advantages: 1. All-dark environment imaging: No active light source is required; targets can be clearly detected even in complete darkness. 2. Strong environmental adaptability: Capable of penetrating interferences such as smoke and dust. 3. All-weather operation**: Operates stably day and night without relying on external lighting conditions. Thanks to its high concealment, strong anti-interference performance and accurate target recognition, infrared thermal imaging technology plays an irreplaceable role in civil fields including military reconnaissance, security monitoring, industrial inspection, medical diagnosis, and fire rescue.