On the correction of attenuation with simultaneous transmit dual-polarization radars

Simultaneous transmission and reception of horizontal and vertical polarized waves (SHV) has become a popular method to achieve dual-polarization radar measurements for operational and research platforms. These systems have numerous advantages and are a cost effective because they do not require two transmitters or a fast mechanical switch as do fast alternating H and V transmit systems (AHV). However it has recently been documented that SHV radar measurements of the differential reflectivity (ZDR) can suffer significant quality problems due to polarization impurities of the H and V signals that result in cross-coupling. These cross-coupling errors have been shown in the literature to occur both as the waves propagate through a medium with non-zero mean canting angles and as a result of antenna polarization errors. The cross-coupling ZDR errors resulting from antenna polarization errors have been shown to depend on the co-polar differential phase (Φ_DP), thus impacting measurements in rain. Because the ZDR bias changes with the Φ_DP, the principle of self-consistency among the dual-polarimetric variables of Z, ZDR and specific differential phase (KDP) is violated.

Several methods for attenuation and differential attenuation correction at various wavelengths that utilize the self-consistency principle have been developed. These methods have numerous advantages including being less sensitive to variations of drop size distribution than conventional techniques. However for SHV radars the principle of self-consistency is violated. The goal of this study is to determine the impact of the antenna polarization cross-coupling ZDR errors in attenuation correction using self-consistency methods through theoretical computations and experimental data analysis. The data were collected by a mobile X-band (SHV) radar co-located with the NCAR S-Pol (AHV) radar. Results from the calculations and data analysis will be presented.