C-Band Attenuation by Tropical Rainfall in Darwin, Australia, Using Climatologically Tuned Ze-R Relations

David Atlas NASA/Goddard Space Flight Center, Greenbelt, Maryland, and Jet Propulsion Laboratory, Pasadena, California

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Daniel Rosenfeld The Hebrew University of Jerusalem, Jerusalem, Israel

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David B. Wolff Applied Research Corporation, Landover, Maryland

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Abstract

The probability matching method (PMM) is used as a basis for estimating attenuation in tropical rains near Darwin, Australia. PMM provides a climatological relationship between measured radar reflectivity and rain rate, which includes the effects of rain and cloud attenuation. When the radar sample is representative, PMM estimates the rainfall without bias. When the data are stratified for greater than average rates, the method no longer compensates for the higher attenuation and the radar rainfall estimates are biased low. The uncompensated attenuation is used to estimate the climatological attenuation coefficient. The method is applicable to any wavelength. The two-way attenuation coefficient was found to be 0.0085 dB km−1 (mm h−1)−1.08 for the tropical rains and associated clouds in Darwin for the first 2 months of the year for horizontally polarized radiation at 5.63 GHz. This unusually large value is discussed. The risks of making real-time corrections for attenuation are also treated.

Abstract

The probability matching method (PMM) is used as a basis for estimating attenuation in tropical rains near Darwin, Australia. PMM provides a climatological relationship between measured radar reflectivity and rain rate, which includes the effects of rain and cloud attenuation. When the radar sample is representative, PMM estimates the rainfall without bias. When the data are stratified for greater than average rates, the method no longer compensates for the higher attenuation and the radar rainfall estimates are biased low. The uncompensated attenuation is used to estimate the climatological attenuation coefficient. The method is applicable to any wavelength. The two-way attenuation coefficient was found to be 0.0085 dB km−1 (mm h−1)−1.08 for the tropical rains and associated clouds in Darwin for the first 2 months of the year for horizontally polarized radiation at 5.63 GHz. This unusually large value is discussed. The risks of making real-time corrections for attenuation are also treated.

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