1/1/2024 0 Comments Raindrop shape rashEstimators of the DSD parameters are presented in section 4, and the impact of measurement errors on the estimates are discussed in section 5. Section 2 describes the raindrop size distribution and its parameters, whereas section 3 describes the shape of raindrops and its implication for polarimetric radar measurements. This paper presents algorithms for the estimation of parameters of a gamma DSD from polarimetric radar measurements. A combination of the three radar measurements ( Z h, Z dr, and K dp) can be utilized to estimate the DSD, specifically the parameters of a parametric form of the DSD such as the gamma DSD. The weighting of the DSD by Z dr and K dp is controlled by the variation of mean raindrop shape with size. The specific differential propagation phase ( K dp) is a forward scatter measurement ( Seliga and Bringi 1978 Sachidananda and Zrnić 1987) whereas the radar reflectivity ( Z h) and Z dr are backscatter measurements. The nonspherical shape of raindrops results in anisotropic propagation of electromagnetic waves, with a difference in the propagation constant at horizontal and vertical polarization states. A general gamma distribution model was suggested by Ulbrich (1983) to characterize the natural variation of the DSD. Careful intercomparisons between radar measurements of Z dr and D 0 derived from surface disdrometers and airborne imaging probes have shown that D 0 can be estimated to an accuracy of about 10%–15% (see, for example, Aydin et al. Seliga and Bringi (1976) showed that Z dr, for an exponential DSD, is directly related to the median volume diameter ( D 0). The disdrometer based evaluations confirm the accuracy of the algorithms developed herein.Įver since the introduction of differential reflectivity ( Z dr) measurement, one of the long standing goals of polarimetric radar has been the estimation of the raindrop size distribution (DSD). The estimators for the raindrop size distribution parameters are also evaluated using disdrometer data based simulations. It is shown that the drop median diameter can be estimated to an accuracy of 10%, whereas the equivalent intercept parameter can be estimated to an accuracy of 6% in the logarithmic scale. The estimator for D 0 as well as other parameters are evaluated in the presence of radar measurement errors. Differential reflectivity is the most closely related measurement to a parameter of the drop size distribution, namely, the drop median diameter ( D 0). Algorithms to estimate the parameters of a gamma raindrop size distribution model from polarimetric radar observations of reflectivity, differential reflectivity, and specific differential phase are developed. Estimation of raindrop size distribution over large spatial and temporal scales has been a long-standing goal of polarimetric radar.
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