Long-Term Assessment of the Reflectivity Biases and Wet-Radome Effect Using Collocated Operational S- and C-Band Dual-Polarization Radars

This study assessed the long-term radar reflectivity (Z) biases of collocated S- and C-band dual-polarization radars. The systematic bias, wet-radome effect (WRE), and attenuation effect were investigated. The algorithm of self-consistency utilizes Z, differential reflectivity (Zdr), and a specific differential phase (Kdp) to estimate the systematic bias and WRE of both radars. Eleven years of disdrometer data in northern Taiwan were used to obtain the self-consistency and Kdp-based attenuation correction relation coefficients. Subsequently, a series of sensitivity tests were conducted to examine the influence of these coefficients on bias and attenuation corrections. The Kdp(Z,Zdr) relationship outperformed that of Kdp(Z). The Kdp(Z,Zdr) relationship with seasonal coefficients and systematic bias-corrected Zdr constituted the optimal procedure. The corrected Z of collocated radars was in good agreement, lending further validity to the correction schemes. The results demonstrated that the stable systematic bias values of two radars were -1.89 to -1.14 dB and -2.46 to -1.87 dB. During the WRE period, additional underestimations of Z by nearly 4 and 7 dB were recorded for S- and C-band radars, respectively. The mean value of radar reflectivity near radar (Znr) was obtained to identify the WRE period. In this study, an innovative quadratic polynomial fitting equation was proposed to investigate the systematic and WRE biases using Znr. Moreover, a pronounced wind intensity dependency of the WRE could be observed in the quadratic polynomial fitting equation.