Real-Time Adjustment Scheme of Radar Precipitation Data at DWD

Within the project RADOLAN (Radar Data Online Adjustment) the Deutscher Wetterdienst (DWD) is developing an adjustment scheme of radar precipitation data which will work in real-time from the year 2003 for hydrological purposes. Therefore the already installed real-time rain gauge network of the Federal State of Baden-Württemberg is used for adjusting the radar measurement of the radar locations of Feldberg/Schwarzwald and of Türkheim/Schwäbische Alb.

As input the precipitation data from the radar network of the DWD in time-intervals of five minutes and from the rain gauge network in time-intervals of one minute will be sampled. For purposes of flood warning it is sufficient that only high precipitation amounts are detected. Therefore in a first step every five minutes a radar-derived algorithm selects the required rain gauge data sets.

The clutter echos of the radar data will be suppressed by an actual clutter radar map. A temporal and spatial variable Z/R-relationship and the so-called climatological adjustment parameter, based on the long-term gauge-radar-comparison, will be applicated. The actual radar precipitation data are compared with the rain gauge measurements at available gauge locations. The gauge-radar-ratios resp. gauge-radar-differences will be interpolated for every radar-pixel. The multiplication resp. addition of the original radar data with these pixel-interpolated quantities results in the adjusted radar map.

For obtaining an adjustment quality criterion only one part of the gauges is used for the adjustment. The other part serves as control stations. The deviation between adjusted radar data and the control gauge data will decide whether the adjustment scheme is good enough. Only the operational run in real-time will bring enough information for further investigation of the usefulness of the adjustment scheme of precipitation radar data.