Quality Control for polarimetric Radar Measurements

Abstract

Polarimetric radar measurements have improved quantitative precipitation estimation especially for the derivation of precipitation amounts. Several weather services are planning therefore to upgrade their radars with polarimetric diversity capabilities. The quality of the rain rate estimation depends strongly on the quality of the polarimetric measurements themselves. The latter, however, will be encoded in a single quality index field which is transferred together with the observational data to the user. The quality index field bases on results achieved in research over the last 25 years and will contain information about (i) broadening of the radar beam and height of the first radar echo; (ii) ground clutter contamination and beam shielding; (iii) contamination by attenuation; (iv) homogeneous beam filling; and (v) a consistency check between reflectivity, differential reflectivity ratio, and differential propagation phase. While (i) to (iii) are also important for conventional weather radars, the later two are focus solely on polarimetric radar observations. The consistency check is used for instance to monitor the performance of the radar system and reveal areas consisting of rain. Since the assumptions for the consistency check are valid only in rain, this check will fail in regions with other types of hydrometeors. In those regions the polarimetric rain rate estimation is not possible and other, conventional, methods have to be used. For further refinement of the quality index field different weights for each factor can be set depending on the weather situation and the preferences of the user.