Quality of Echotop Products and Derived Probability of Hail as a Function of Range

Operational hail detection products at KNMI (Netherlands) and RMI (Belgium) are derived from the height of the freezing level and the 45-dBZ echotop values provided by single-polarization C-band weather radars. Echotop products are not only affected by errors on the measured reflectivity it self but also by errors on the height assigned to the measured reflectivities. In this study, we evaluate the relative importance of these errors as a function of range.

The method is based on the comparison between the reflectivity field observed by the radar of Wideumont in Belgium and the radar of De Bilt in The Netherlands on a vertical cross section extending between the two radars. Our results show that the measurement quality of maximum reflectivity and echotop values are not affected by range effects up to a distance of about 150 km. Within this range height assignment errors are generally less than 1 km and the impact of these errors on the derived probability of hail is small compared with the impact of calibration errors.