Improved Estimation of the Specific Attenuation and Backscatter Differential Phase over Short Rain Paths

Abstract

In radar polarimetry, the differential phase ΨDP consists of the propagation differential phase ΦDP and the backscatter differential phase δhv. While ΦDP is commonly used for attenuation correction (i.e., estimation of the specific attenuation A and specific differential phase KDP), recent studies have demonstrated that δhv can provide information concerning the dominant size of raindrops. However, the estimation of ΦDP and δhv is not straightforward given their coupled nature and the noisy behavior of ΨDP, especially over short paths. In this work, the impacts of estimating ΦDP on the estimation of A over short paths, using the extended version of the ZPHI method, are examined. Special attention is given to the optimization of the parameter α that connects KDP and A. In addition, an improved technique is proposed to compute δhv from ΨDP and ΦDP in rain. For these purposes, diverse storm events observed by a polarimetric X-band radar in the Netherlands are used. Statistical analysis based on the minimum errors associated with the optimization of α and the consistency between KDP and A showed that more accurate and stable α and A are obtained if ΦDP is estimated at range resolution, which is not possible by conventional range filtering techniques. Accurate δhv estimates were able to depict the spatial variability of dominant raindrop size in the observed storms. By following the presented study, the ZPHI method and its variations can be employed without the need for considering long paths, leading to localized and accurate estimation of A and δhv.