The Radio Noise Environment in Near Space: A Review

With the advent of the space age it has become im­ portant to extend our knowledge of the radio noise en­ vironment beyond the confines of the Earth itself. This review summarizes the characteristics of the near space electromagnetic ambient in terms of frequency, space and time variations, and identifies major sour­ ces. In the HF and lower bands where most noise and interference come from magnetospheric processes or ground-based natural (thunderstorms) and man-made (transmitter) sources, sufficient satellite and space­ craft data are available to describe the ambient in some detail. At VHF and UHF few in situ measurements exist, so several theoretical models have been attemp­ ted. Modeling approaches require assessment of frequ­ ency assignments (or preferably frequencies actually in use), transmitter powar outputs, antenna radiation patterns, geographic distributions of transmitters and source types (e.g., TV or FM broadcast stations, radar). These factors must be considered in relation to the re­ gion of space of interest. Model validations may be made partially by aircraft surveys, but more precisely by satellite or spacecraft measurements. The Space Shuttle/Spacelab vehicle will be particularly valuable for RF environment surveys.