The Influence of Antenna Radome on Weather Radar Calibration and Its Real-Time Assessment

Operational weather radars are usually equipped with a radome to reduce the wind load on the antenna and to allow continuous operation under bad weather conditions. The study is focused on quantifying the impact on radar polarimetric measurements due to the presence of a radome. Analysis refers to the transportable X-band polarimetric radar of the Agenzia Regionale per la Protezione Ambientale (ARPA) Piemonte (ARX), which uses a ``bullet shaped'' radome to provide environmental protection to the antenna and receiver apparatus system. Radar calibration is performed using wet and dry radomes. Differential reflectivity calibration results are compared with those obtained using the sun as a radiation reference source. Estimates have comparable mean values, with their differences being within the standard deviation. The paper describes a method based on the self-consistency principle that takes into account the loss induced by radome wetting due to rain to adjust the absolute calibration of the radar in real time. To verify how well this method overcomes the problem of excess attenuation caused by the presence of precipitation on the radome, two validation methods are presented. The first uses an empirical model to estimate the two-way wet radome losses for a qualitative comparison, with the corresponding losses obtained by the self-consistency principle. The second employs comparisons between radar and gauge rainfall accumulations with and without radome correction. This approach offers a clear understanding of the response of the correction, providing quantitative performance in a real case.