Analysis of the Variability in the Raindrop Size Distribution and Its Effect on Attenuation at 20-40 GHz

A key problem in determining the level of attenuation from the rainfall rate is the considerable variability in the raindrop size distribution. This letter investigates the effects of the variability of the raindrop size distribution (DSD) on the estimation of specific attenuation. Disdrometer data from three sites in the U.K. were analyzed to derive the three parameters (D_m, mu, and N_w) of the normalized gamma distribution. The statistics of the parameters were analyzed as a function of time of year and rainfall intensity. From the raindrop size distribution data, the impact on attenuation at 20-40 GHz was investigated. A simple model to quantify the uncertainty of the raindrop size distribution has been created. Finally, we have shown qualitatively that differences between measured and modeled attenuation can partly be explained by uncertainty in the raindrop size distribution. Furthermore, we also show that although the model for mean attenuation is relatively constant, the standard deviation is much more variable even for sites in close proximity.