The radio noise emitted by all matter, while used as a source of information in radioastronomy and remote sensing, may be a limiting factor in communication services. Sources of radio noise of interest on Earth-space paths are the atmosphere, clouds, rain, extraterrestrial sources, and noise from the surface of the Earth. Prediction methods are given in Recommendation ITU-R P.372. Fundamental information about radio noise and galactic sources is given in [Kraus, 1966].