Correction of Radar Reflectivity in Partial Beam Blockage Regions of S-band Dual-Polarization Radar

Radar beam blockage caused by terrain, tree and manmade structures limits radar coverage and leads to biases in radar measurements at low elevation angles. This study aims to develop the correction technique for radar reflectivity in partial beam blockage (PBB) regions based on self-consistency principle between intensity and phase measurements from dual-polarization radar. The proposed method utilizes K_DP-Z_H relationship (K_DP=3.77×10^-5 Z_H^0.9) as determined from scattering simulation for S-band using DSDs in Korea.

To remove ground echoes and non-meteorological echoes, the simple and fast procedure was applied using the radial texture of Z_H, Z_DR, Φ_DP, ρ_hv, and threshold of ρ_hv (> 0.98). To alleviate contamination from bright band, radar coverage is limited below melting layer that is determined via combination of 0°C isotherm height from radiosonde measurements and morphologic bottom height of bright band in quasi-vertical profile of reflectivity. The system bias of Z_H (=-4.41dB in this study) is then calibrated by self-consistency principle using entire volume scans. The blockage bias of Z_H in PBB is calculated at each ray using measured Φ_DP (Φ_{DP_obs}) and calculated Φ_DP (Φ_{DP_cal}) by integrating of calibrated Z_H along radial direction. Concretely, the PBB bias of Z_H is derived from the slope between Φ_{DP_obs} and Φ_{DP_cal}. To improve the accuracy of PBB bias, both Φ_{DP_obs} and Φ_{DP_cal} larger than 3° are used.

The performance of the propopsed method is evaluated by comparing with rainfall rain gauges. After applying the proposed method, the significant increases of radar rainfall in the blocked radials were found. The relative error was also reduced in the blocked radials. The correlation coefficient and bias ratio increased from 0.85 to 0.88 and from 0.71 to 0.77, respectively. The standard deviation and normalized standard deviation decreased from 1.82 mmhr^-1 to 1.58 mmhr^-1 and from 0.50 to 0.43, respectively.

Acknowledgments

This research is supported by “Development and application of Cross governmental dual-pol radar harmonization (WRC-2013-A-1)” project of the Weather Radar Center, Korea Meteorological Administration.