Four-Dimensional Merging of Polarimetric Weather Radar Scans in Germany at X and C Band Wavelenghts

Single weather radar stations suffer from spatial coverage insufficient for complete description, tracking, and life-cycle analysis of medium to large storm systems. Spatial resolution and sensitivity decrease with increasing range, while ground clutter and scan time constraints compromise coverage close to the radar. Additionally errors in calibration, attenuation, partial beam blockage (PBB), and displacement through advection can lead to inconsistencies between observations from different scans. With the advent of polarimetric weather radar networks, attenuation and the consequent loss in sensitivity can be estimated more precisely, while PBB and calibration errors can be estimated through consistency relations between spatiotemporal accumulations of reflectivity ZH and specific differential phase shift KDP.

The Geoverbund ABC/J test bed area in western Germany features two dual-polarimetric X Band weather radars with largely overlapping measurement areas, in addition to overlap with the C-Band radar network of the German Weather Service. A 4D composite volume scan merging scheme which takes into account advection, radar sensitivity, attenuation, partial beam blockage, ground clutter, and ship radar interference is applied to these measurements. Expected and observed differences in measurements at X and C Band frequencies are discussed, also in reference to combination of both frequencies. First results of composite QPE and polarimetry-based hydrometeor classification are shown with respect to calibration precision, vertical profiles of reflectivity, and resolution. Results and data quality are discussed in relation to operational products for QPE and object based analysis used in associated research projects and local water management facilities.