Use of dual‐frequency microwave links for measuring path‐averaged rainfall

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Abstract
Results are presented from an experiment designed to test the use of dual‐frequency microwave attenuation for measuring path‐averaged rainfall. In general, the relation between attenuation and path‐averaged rainfall is nonlinear. However, for carefully chosen pairs of frequencies, the relation between the difference in attenuations and path‐averaged rainfall is well represented by a straight line through the origin. The slope of this line is essentially unaffected by variations in the (unknown) drop size distribution, drop shape, and drop temperature. This paper describes the results obtained from a pair of links operating at 12.8 GHz and 17.6 GHz on a 23.3 km path. Results are shown for three individual events, including comparisons with rainfall estimates obtained from more traditional sources: a local rain gauge network and an adjacent weather radar. We report summary results for 112 events recorded on this path during almost 2 years of observation, and also for 52 events recorded on a nearby 13.9 km path operating at 13.9 GHz and 22.9 GHz. In both cases the results suggest that dual‐frequency links could serve as useful additional tools for the measurement of rainfall, particularly in locations such as urban areas and obscured mountain valleys, where traditional measuring instruments struggle to provide accurate estimates.

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