Microphysical Interpretation of Multi-Parameter Radar Measurements in Rain. Part I: Interpretation of Polarization Measurements and Estimation of Raindrop Shapes

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  • 1 Illinois State Water Survey, Champaign, IL 61820
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Abstract

The backscattered electric field received by a radar is related to the transmitted field by a backscatter matrix. In the case of single raindrops the elements in this matrix are determined by raindrop size and shape. At long radar wavelength certain combinations of elements, however, only depend on raindrop shape. These combinations form the basis of current linear and circular polarization measurables.

An ensemble of raindrops will usually exhibit a variety of shapes because of the variation in raindrop size and because of oscillations induced by drop oscillations. This shape variation can be described by an axis ratio distribution. Since at long wavelengths in rain the radar polarization measurables are largely determined by shape, they are sensitive to this axis ratio distribution. In this study, the sensitivity of some linear and circular polarization measurables to the mean and variance of the raindrop axis ratio distribution is investigated. These measurables are then used to formulate estimators of radar-power-weighted mean axis ratio and variance. These estimators appear to be applicable to a wide variety of drop size distributions.

Abstract

The backscattered electric field received by a radar is related to the transmitted field by a backscatter matrix. In the case of single raindrops the elements in this matrix are determined by raindrop size and shape. At long radar wavelength certain combinations of elements, however, only depend on raindrop shape. These combinations form the basis of current linear and circular polarization measurables.

An ensemble of raindrops will usually exhibit a variety of shapes because of the variation in raindrop size and because of oscillations induced by drop oscillations. This shape variation can be described by an axis ratio distribution. Since at long wavelengths in rain the radar polarization measurables are largely determined by shape, they are sensitive to this axis ratio distribution. In this study, the sensitivity of some linear and circular polarization measurables to the mean and variance of the raindrop axis ratio distribution is investigated. These measurables are then used to formulate estimators of radar-power-weighted mean axis ratio and variance. These estimators appear to be applicable to a wide variety of drop size distributions.

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