Effect of rain on 4 GHz troposcatter radio paths

The letter discusses field-strength measurements made with a narrow-beam scanning receiving aerial on an occasion when widespread rain embraced two 4 GHz transhorizon radio paths, the modification to the angular distribution of the troposcatter energy brought about by the rain being used to indicate the presence of rain scatter. A weather radar and rain gauges distributed along the paths aided the interpretation of the results. It is suggested that rain on such paths is not likely to contribute significantly to the path-loss statistics, but rain may cause significant changes in the mean direction of arrival of the scatter signals, whereas clear-air inhomogeneities in the refractive index produce somewhat smaller changes.