Influence of Ground Clutter Contamination on Polarimetric Radar Parameters

Abstract

The influence of ground clutter contamination on the estimation of polarimetric radar parameters, horizontal reflectivity (Z_h), differential reflectivity (Z_dr), correlation coefficient (ρ_hυ), and differential propagation phase (ϕ_dp) was examined. This study aims to derive the critical level of ground clutter contamination for Z_h, Z_dr, ρ_hυ, and ϕ_dp at which ground clutter influence exceeds predefined precision thresholds. Reference data with minimal ground clutter contamination consist of eight precipitation fields measured during three rain events characterized by stratiform and convective precipitation. Data were collected at an elevation angle of 0.8° by the Météo-France operational, polarimetric Doppler C-band weather radar located in Trappes, France, ∼30 km southwest of Paris. Nine different ground clutter signatures, ranging from point targets to more complex signatures typical for mountain ranges or urban obstacles, were added to the precipitation fields. This is done at the level of raw in-phase and quadrature component data in the two polarimetric channels. For each ground clutter signature, 30 simulations were conducted in which the mean reflectivity of ground clutter within the resolution volume varied between being 30 dB higher to 30 dB lower than the mean reflectivity of precipitation. Differences in Z_h, Z_dr, ρ_υ, and ϕ_dp between simulation and reference were shown as a function of ratio between ground clutter and precipitation intensities. As a result of this study, horizontal reflectivity showed the lowest sensitivity to ground clutter contamination. Furthermore, a precision of 1.7 dBZ in Z_h is achieved on average when the precipitation and ground clutter intensities are equal. Requiring a precision of 0.2 dB in Z_dr and 3° in ϕ_dp, the reflectivity of precipitation needs to be on average ∼5.5 and ∼6 dB, respectively, higher compared to the reflectivity of ground clutter. The analysis also indicates that the highest sensitivity to the nine clutter signatures was derived for ρ_hυ. To meet a predefined precision threshold of 0.02, reflectivity of precipitation needs to be ∼13.5 dB higher than the reflectivity of ground clutter.