Monitoraggio della qualità dati di radar meteorologici a doppia polarizzazione

Weather radar data are used for precipitations monitoring but also for quantitative applications, such as rainfall estimation, short-term weather prediction and initialization of numerical atmospheric and hydrological models. Therefore, the data quality of radars must be ensured and continuously monitored. Specifically, the stability of the radar calibration is a mandatory aspect for performing reliable rainfall measurements. Over the years, many calibration techniques based on external sources have been developed, e.g. calibration with the Sun, and based on fixed and well-known targets, e.g. calibration with ground clutter echoes. Ground clutter calibration is implemented in this work on horizontal and vertical reflectivity and its results show that it is possible to promptly recognize hardware failures and calibration issues. The Sun calibration provides information about the receiver chain and the antenna pointing. Small biases on azimuth and elevation are found. To evaluate the quality of the radar reflectivity measurements during rainfalls, an intercalibration technique is performed comparing measurements collected by two radars on overlapping regions. The physical consistency of polarimetric radar observables is finally analyzed using the self consistency approach based on power and phase measurements. In addition to the aforementioned calibration techniques, a specific methodology based on image processing is developed to remove the interferences from artificial radio emitters. The set of methods considered is shown to provide a robust tool for online monitoring of the radar calibration. The attainable accuracy for the calibration of the radar reflectivity is about 1dB, which is considered adequate for most quantitative applications.