Validation of polarimetric methods for attenuation correction at C band

Polarimetric methods for attenuation correction of radar reflectivity Z and differential reflectivity Z_DR utilize measurements of differential phase Φ_DP which is immune to attenuation. Simplified versions of the attenuation correction techniques assume that the coefficients of proportionality α and β between the Z and Z_DR biases and Φ_DP do not vary much. However, at C band these are highly variable in convective cells containing large raindrops and hail due to effects of resonance scattering. More sophisticated schemes for attenuation correction attempt to estimate the coefficients α and β in such “hotspot” cells using additional constraints.

In this paper, we evaluate the performance of the attenuation correction techniques with different degree of complexity using C-band data collected with the Environment Canada King radar in Southern Ontario, Canada, and the EEC Sidpol radar in Alabama, USA.

Nearby S-band WSR-88D radars in Buffalo and Panama City are used to validate attenuation correction of Z. Checking consistency between corrected Z and specific differential phase K_DP is another validation tool.

The criteria of spatial and temporal continuity of the Z_DR fields as well as consistency with expected values of Z_DR in dry aggregated snow and light rain are utilized to assess the quality of differential attenuation correction.

Statistical analysis of variable coefficients α and β in “hotspots” reveals noticeable differences in microphysical processes which determine precipitation formation in Ontario and Alabama.