Correction algorithm of the Vertical Reflectivity Profile (VRP) for the German Met. Service

Beside the conversion of radar reflectivity into rainrate, the correction of the Vertical Reflectivity Profile is one of the major tasks of quantitative radar measurements. Especially, when the radar beam intersects the Bright Band an obvious overestimation of the rainrate would occur. The algorithm which will be presented is the first of this kind in the German Met. Service (DWD). It is based on CAPPIs with a resolution of 1 km to supply comparable pixels and profiles with the same horizontal and vertical resolution not depending on radar range any more. As the correction is necessary primarily because of Bright Band influence which is more typical for stratiform than for convective rain, a pattern recognition algorithm which separates convective cells from stratiform rain fields is passed first. The VRP-correction only manipulates pixels which are classified stratiform. For areas with similar profiles a mean Vertical Reflectivity Profile with a higher vertical resolution is chosen from a current ring buffer. By different means of averaging a characteristic profile for each connected rain field is established, then. The ring buffer consists of several hundred profiles derived from the interior zone of the Volumescan from one year of radar data. They are separated into classes of Bright Band altitude. The buffer is modified after each Volumescan by recent profiles from the interior zone of this scan. The selection of profiles from it is based on profile similarities and Bright Band level. The algorithm is in test stage at the moment. Its applicability for all radar sites has to be checked before it's used for the German quantitative radar products.