Radiation emitted by the EarthÕs surface, the atmosphere and by clouds. Also known as terrestrial and long-wave radiation. Infrared radiation has a distinctive spectrum (i.e., range of wavelengths) governed by the temperature of the Earth-atmosphere system. The spectrum of infrared radiation is practically distinct from that of solar (q.v.) or short-wave radiation because of the difference in temperature between the Sun and the Earth-atmosphere system.