A new polarimetric method for correcting the effects of attenuation at C-band

Attenuating echoes are known to reduce the values of reflectivity and differential reflectivity (Z, ZDR). It has been noted in the literature that a quasi-linear relationship exists between specific differential phase shift (KDP) and attenuation (A). Several different approaches with accompanying assumptions have been adopted in order to constrain the KDP-A relationship so that the constant of proportionality can be determined. A new approach has been developed that is independent of assumed raindrop size-shape model, permits nonlinear relationships which may result due to temperature-dependent attenuation, and is empirical.

The advection-correction scheme is based on the assumption that changes in Z and ZDR over a 5-min duration are, in the mean, due to attenuation alone. A cross-correlation analysis is used to advect observations of Z, ZDR and differential phase shift forward in time. These advected fields are then compared to observations valid at that time. All data points are then put into a matrix system where the attenuation vector is solved through minimisation of a cost function. This vector may then be used to correct values of Z and ZDR provided a polarimetric measurement of differential phase shift. Radar reflectivity comparisons made with neighboring radars show favourable results.