Radiometers are instruments which measure radiative intensities within a particular frequency window. A radiometer is further identified by the portion of the electromagnetic radiation it covers, usually the infrared or microwave regions. Normally the spectral range extends from the longwave (14-15 micron) to the shortwave (3-4 micron). This range overlaps much of the emission spectrum of Earth. The technology is classified in broadband radiometer of spectral radiometers depending on the spectral resolution. A radiometer measures the intensity of the radiative energy, but does not differenciate between the different registered wavelengths or their respective amplitude. In other terms, it provides a single value as combined result of all wavelengths within the considered frequency window.