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Evan J. Dutton and Francis K. Steele

Abstract: In the presence of rain, millimeter–wave propagation is acutely sensitive to the distribution of raindrop sizes along a given propagation link. This report analyzes the variability of rain attenuation prediction at microwave/millimeter wave frequencies caused from the variation of measured raindrop–size distribution data. The results show a considerable need for better and more extensive dropsize distribution data, both in time and geography. After searching for potential solutions, the report discusses the historical development of raindrop distribution measurement methodology, including direct measurement techniques, but with emphasis on indirect, or remote sensing, multiple frequency techniques. These latter techniques are carefully scrutinized, with the conclusion that some information derived separately from the techniques is usually necessary to successful usage of the techniques. Some concluding observations are then made for the selection of an appropriate remote-sensing technique for the improved determination of path-averaged raindrop–size distributions.

Keywords: millimeter waves; raindrop-size distributions; annual variability; attenuation coefficients; multiple frequency techniques; prediction variability

Disclaimer: Certain commercial equipment, components, and software may be identified in this report to specify adequately the technical aspects of the reported results. In no case does such identification imply recommendation or endorsement by the National Telecommunications and Information Administration, nor does it imply that the equipment or software identified is necessarily the best available for the particular application or uses.

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