The Dimensions of Radio Noise

The radio noise field is composed of naturally occurring emissions from atmospheric and galactic processes, man-made disturbances and thermal radiation from the local environment. Natural noise processes including thermal radiation contribute the dominant noise at the extremes of the radio spectrum in metropolitan environments but are superseded by man-made noise in the LF to UHF bands. The dominance of man-made noise in the center of the radio spectrum arises from coherent interference of entertainment, communication, and navigational equipment and the incoherent emissions of transportation, utility, industrial and commercial equipment. The source emission spectra and the propagation characteristics of the source-to-detector space control the noise intensity. The intensity of coherent noise is predictable from a knowledge of the number, location, modulation and carrier frequency of the sources and the physical properties and features of the transmission space. The intensity of incoherent interference is similarly dependent but complicated by being produced from statistically random processes. The prediction and ultimately the control of incoherent radio noise is yielding to analyses and measurements which combine examinations of the dominant individual source spectra and the composite spectrum of area noise sources. The multi-dimensional area signatures of composite, incoherent radio noise can be used to identify an area from observation points located throughout the local hemisphere.