We know that objects with temperatures above absolute zero (-273 C) will have continuous electromagnetic radiation. But the radiation energy of different objects is different. In order to measure the electromagnetic radiation energy of objects, people set a standard-absolute blackbody. Absolute blackbody refers to an object whose absorption coefficient of electromagnetic radiation of various wavelengths is always equal to 1 at any temperature. There is no absolute black body in nature. Absolute blackbody is an idealized reference model. In the remote sensing thermal infrared scanner system, high-temperature blackbody and low-temperature blackbody are installed as reference sources for detecting thermal radiation of ground objects. Practical absolute blackbody is made by manual method. Generally speaking, the radiant energy of an object is related to its surface temperature. The higher the temperature, the greater the radiant energy. In other words, when the radiant energy of an object changes with its temperature, the spectral distribution of radiant energy also changes.