Black body terminology is important thing in remote sensing scince. When I was in Bulgaria for Geoscientific Conference, Professor from Turkey asked me about this matter, because his Graduate School of Environment ask him to teach remote sensing for next semester. OK, let’s begin.
Black body is related to electromagnetic energy. Electromagnetic energy can be generated by a number of mechanisms. These include changes in the energy levels of electrons in atoms (line spectra), decay of radioactive materials (e.g. gamma rays), the acceleration of electrical charges, for example in the aerial of a transmitter, and the thermal motion of atoms and molecules. All matter above the absolute zero of temperature (0 K or -273.16 degree Celcius) emits radiation. This is due to the internal motion of the constituent atoms and molecules, which becomes more energetic as the temperature increases.
Each source of radiations emits a characteristic spectrum of different wavelengths and intensities, and , importantly, because the same internal processes are involved, it can also absorb that same range of radiation. It is usual to consider the behaviour of an ideal source – called a black body. A black body is a body that is a perfect absorber and emitter of radiation. It is defined as a hypothetical object or material that absorbs all radiation incident upon it and emits the maximum amount of radiation possible at that temperature.
Figure above, explain us that spectral distribution of radiation emitted from black bodies at temperature 5800 K , approxemately equal to that of the sun, 800 K and 300 K typical of the earth’s surface showing the region of visible radiation and the large shift in peak emissions between shortwave solar radiation and thermal longwave.
Figure from: http://www.iki.rssi.ru/