## 2 Materials and Methods
### The Latest MeteoSwiss Dual-Polarization Weather Radar (RADAR) Network Data
#### 2.2.3 RADAR-Derived Quantitative Precipitation Estimation  
The MeteoSwiss scan strategy aims at monitoring the four-dimensional variability of the precipitation field to obtain a well-defined vertical reflectivity profile. Each radar performs plan position indicator (PPI) scans at 20 elevations from \(-0.2^{\circ}\) to \(40^{\circ}\) in 5 min. The scans are interleaved so that a representative half-volume of 10 PPI is available every 2.5 min, allowing the precipitation mosaic to be updated at that time interval. Figure 2 in [3] (p. 45) shows the Swiss scan strategy: the 1 st half volume is shown in blue, the 2 nd half volume is in yellow. The scan starts with the sweep #1 at \(6.5^{\circ}\) elevation and ends with the sweep #20 at \(9.5^{\circ}\) (first two numbers). The 3 rd and 4 th number represent the number of antenna rotations per minute and pulse repetition frequency, respectively. The concept and main characteristics are quite similar to those of the previous generation radar network [37] (Table B1, p. 2628). The current refinements include a top-down program, which reduces the risk that the antenna hits its lower mechanical limit and facilitates the implementation of a gradient test in the clutter elimination algorithm, as well as an additional, partially redundant sweep with an angle of elevation of \(1^{\circ}\). This helps improve QPE, especially in mountainous regions. For each sweep, up to six \(1^{\circ}\times 1^{\circ}\times 83\) m clutter-free radar bins compensated for partial shielding, as described in [38], are averaged in linear equivalent radar reflectivity factor Z to derive polar \(1^{\circ}\times 1^{\circ}\times 500\) m radar bins.  
Correction for the vertical profile of reflectivity (VPR) is done using an average profile based on space-time aggregation at the mesobeta scale (a period of a few hours and over the visible part of the area within a maximum range of 70 km). Figure 6 in [39] shows the real \"orography-constrained\" shape of the 70 km cylinder used for deriving the mesobeta profile used in the operational radar data processing. The VPR correction factor spans \(\pm 4.77\) dB, since it ranges from a minimum factor of 0.333 to a maximum of 3. It is a relative correction factor that is set to 1 a few hundred meters below the \(0^{\circ}\) isotherm. VPR is dynamic and is calculated fully automatically with a vertical resolution of 200 m with updates every five minutes when new precipitation comes in. In the absence of precipitation, the operational VPR smoothly converges to a climatological profile with a fixed slope of 1 dB/ km.  
The kilometric estimate of precipitation at ground level is then retrieved through a weighted average of all the available VPR-corrected multi-radar observations aloft. The weights are inversely proportional to the altitude above the ground, but depend also on the radar visibility (zero weight for fully shielded samples). Such weighted averages are then resampled to a 1 km Cartesian grid coincident with the Swiss national coordinate system (CH1903, see last paragraph of Section 2.1 for more details).  
Finally, the 1 km estimate of precipitation at ground level is multiplied with a 1 km map of local adjustment factors derived using the approach described in [38], see in particular \"Experiment G\" in Table 2 (p. 1684), Figure 8 (p. 1686) and Section 5 (\"Local bias correction\").