hail signals were determined from the operational radar network of
German Weather Service (DWD), consisting of 17 Cband radars (locations indicated in Fig. 5; for technical details see
Table 1 in the Appendix A). Each radar measures reflectivity Z within a
radius of 230 km around the location. A distance of less than 200 km
between the single radar stations ensures nearly full spatial coverage.
Ground clutter from fixed objects at low elevations is eliminated by application of a Doppler filter. All radars are calibrated several times a year
by feeding a test signal (continuous wave) into the receiver and comparing the resulting signal from the A/D processor.