An Algorithm for Detecting and Removing the Spurious Differential Phase Observed by C-Band Polarimetric Radar in the Rain

Abstract

In this study, an algorithm was developed to detect the spurious differential phase Φ_DP and specific differential phase K_DP in the rain for application after the removal of gate-to-gate Φ_DP fluctuations. The algorithm is a threshold filter designed based on the empirical relationship between the K_DP and radar reflectivity factor at horizontal polarization Z_H for raindrops. The construction and validation of the algorithm were performed using the data observed by the C-band polarimetric radar on board the research vessel Mirai near Sumatra from 23 November to 17 December 2015, when a pilot field campaign of the Years of the Maritime Continent (YMC) project was conducted. Perturbations exist in the Φ_DP and associated spurious values of K_DP on a 10-km scale in the range direction, which are mainly induced by second-trip echoes and nonuniform beam filling. This new algorithm can efficiently detect these perturbed Φ_DP values and the positively and negatively biased K_DP values. The standard deviation of the K_DP in areas with relatively low Z_H is also significantly reduced by the application of the algorithm. Simultaneously, the estimation of the rain rate from the filtered K_DP has been greatly improved. The results indicate that the algorithm developed in this study can efficiently manage the quality of the data observed not only in the open ocean but also in coastal areas of the Maritime Continent.