Evan J. Dutton

Abstract: Because rain attenuation continues to be a problem for the operation of microwave links worldwide, this report examines the behavior and the prediction of rain rate and rain attenuation·distributions on a worldwide basis. Particular emphasis is placed' on seven areas of the world of special interest. to the Uo S. Army Communications Electronics and Engineering~Installation Agency (USACEEIA). The first part of the report discusses the need for, and provides, an alternative thunderstorm ratio in the Rice-Holmberg rain rate distribution prediction model. This new thunderstorm ratio is more readily obtained in regions of thE~ world with s..parse, and less historical, meteorological data. Comparisons of rain rate distributions predicted from the Rice-Holmberg model with observed distributions are then presented. The second part of the report discusses rain attenuation prediction on terrestrial microwave links .. Ten models, including a newly~derived model for this report, are presented for this purpose. Of these 10 models, however, only 3 contain a year-to-year variability pred"iction feature--a feature usua ll.y necessary to the annua 1 di stri buti on predi ction process. An lI ad hocl! annual variability is attached to thE~ remaining 7 models. All 10 models are then intercompared with observed rain attenuation distribution data. The third, and largest, part of the report presents contour maps of the parameters necessary for annual rain rate distribution predictions. Also presented are contour maps of rain rate distribution prediction results at the 1, 0.1, and 0.01 percentile exceedance levels, for use to the reader in predicting annual rain attenuation distributions at those levels. Seven specific regions of the world have been contoured in this report: 1. the Federal Republic of Germany and vicinity, 2. Okinawa, 3. the Republic of Korea and vicinity, 4. Southwest Asia, 5. Central America, 6. the United States of America, 7. Southeast Asia.

Keywords: rain attenuation; attenuation distributions; contour maps; microwave links; model-data comparisons

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.

For questions or information on this or any other NTIA scientific publication, contact the ITS Publications Office at ITSinfo@ntia.gov or 303-497-3572.

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