## 4 Experimental Results
### Comments  
As can be seen in Figures 7 and 9, the rising of the perturbation causes a visible drop in the power received by the SRS stations. This behavior is exploited to derive the estimated rain intensities. According to the results shown in Figures 8 and 10, and the errors reported in Tables 2 and 3, an overall good level of reliability of the system can be asserted. However, a higher relative accuracy has been achieved for the event on 14 August 2018; the rainfall has been significantly more intense on that date with respect to the 4 July, resulting in a stronger effect on the captured signal. Some of the differences among the estimates can be explained with the particular features of the involved systems. First of all, the rain intensity returned by the radar is based on an empirical model that aims to estimates the rainfall at the ground level on the base of reflectivity measurements of the atmosphere (in [38] a detailed explanation of the algorithm can be found); this can lead to some differences with the readings provided by the RGs, which collect the rain at the terrain level. Moreover, the SRS stations at the Monte Scarpino landfill are located about 3 km away from the AR PAL one at Monte Gazzo (the SRS system and the AR PAL RG belong to different pixels of the radar precipitation map). A more detailed analysis can be carried out focusing the attention on the evolution of the involved meteorological perturbations. In particular, as for the event of 4 July 2018, a time delay of about 20 min can be noted between the peak of the rain intensity sensed by the polarimetric radar of Monte Settepani and the rain intensity's peak measured by the sensors network of the SRS. This behavior can be ascribed to the fact that SRS senses the perturbation when it crosses the station-satellite links while the WR measurements are referred to 1 km\({}^{2}\) tiles of territory. To better understand this point, the rainfall intensity \(\mathcal{R}\) maps of the WR taken at 1:10 UTC, 2:00 UTC (corresponding to the rain intensity peak according to the WR), 2:40 UTC, and 3:30 UTC are reported in Figure 11a-d for the event on 4 July 2018. It can be noticed that the perturbation is traveling toward the landfill area (represented by the red cross) coming from the north-west direction, whereas, as it can be deduced from Figure 3b, the station-satellite links are located at the south of the landfill. Therefore, the perturbation is not intercepted by the station-satellite links until it arrives in the very proximity of the Scarpino landfill. Such an effect can be effectively mitigated by considering satellite microwave links covering a larger portion of territory than the monitored catchment in order to nowcast precipitation fronts approaching from the north quadrants. Nevertheless, the delay of the rainfall's peak perceived by the SRS with respect to the RG is only 5 min. As for the event on 14 August 2018, on the other hand, the perturbation was born at the south of the landfill, and so it was detected by SRS with no delay. In Figure 12a-d, the related rainfall intensity \(\mathcal{R}\) maps generated by the WR, at 8:00 UTC, 8:50 UTC, 9:50 UTC (corresponding to the rain intensity's peak according to the WR), and 10:50 UTC are shown. About the RG's data, two strong peaks are present that cannot be found in the WR and SRS's outputs; these differences are probably due to the distance of 3.55 km existing between the RG and the landfill, which sometimes can lead to significantly different punctual readings.