Analysis and Correction of System Bias of Differential Reflectivity for X-Band Dual Polarization Radars in Beijing Area

Differential reflectivity （ZDR） is a crucial polarimetric parameter reflecting the morphology of cloud and precipitation particles.However， the quality of ZDR is highly susceptible to decline due to hardware equipment and environmental influences.Analyzing biases in the measurement of ZDR and conducting corrections are key for the effective application of dual-polarization radar data.In this study， an analysis of the biases in ZDR is conducted， and corrective strategies are proposed based on data collected from light rain events by eight X-band dual-polarization radars in Beijing during July 2023.An adopted radial-by-radial accumulation method is employed to investigate factors and magnitudes influencing ZDR.Furthermore， the system bias of ZDR of full volume scans is corrected by using extensive raindrop spectrometer data during the corresponding period.The median value of ZDR computed via the T-matrix method of raindrop spectrometer data serves as the reference for the correction process.The following conclusions are drawn： （1） Lightning rods exert a significant influence on X-band radar’s ZDR in Beijing， with impact extending from 10° to 25° azimuth angles and average amplitude ranging from 0.16 dB to 1.21 dB.（2） ZDR data obtained from Mentougou and Huairou radars are not only affected by lightning rods but also by nearby iron towers and signal towers， with smaller azimuth angles of impact compared to lightning rods.（3） Partial beam blockage significantly affects ZDR， introducing notable systematic biases.For Fangshan X-band radar， partial beam blockage contributes to an increase of 1.19 dB in differential ZDR.（4） The proposed method for system bias correction demonstrates effective mitigation of unreasonable ZDR values attributed to factors such as lightning rods and beam blockage across all elevation angles and radial distances.