## 4 Results
### Assessment Results
#### 4.3.2 Comparison with the Flood Risk Map  
The flood hazard map (Figure 4) provided by the Italian Ministry of the Environment and Land Protection was used to assess the reliability of the proposed approach. All the ALICE\({}_{\text{NDSI}}\) anomalous pixels detected by RST-FLOOD in the 4-8 December 2013 temporal range have been superimposed on the PAI area (Figure 12).  
Table 3 summarizes the amount of anomalous pixels falling or not within the PAI area, counted considering both the whole scene and the above-mentioned black box (shown in Figure 12b).  
Figure 11: (**a**) Comparison between the flooded affected areas detected by RST-FLOOD for the 5 December 2013 (orange pixels) and the water affected areas computed by a change detection scheme on Landsat data (magenta pixels); the common pixels are highlighted in green; (**b**) a magnified map of (**a**) within the white box shown in Figure 1.  
Figure 12: (**a**) PAI and anomalous pixels detected by RST-FLOOD (ALICE\({}_{\text{NDSI}}\geq\) 3) in 4-8 December 2013 over the ROI; (**b**) a magnified map of (**a**) within the white box shown in Figure 1.  
The analysis of the results reveals that 68% of detected pixels within the whole ROI were in agreement with the PAI area. In addition, looking at Figure 12a, only a very low number of pixels seem to not be directly correlated with the hydrographic network of the ROI, indicating a general good reliability of the achieved results. In more detail, among the 32% of detections outside PAI area (equal to 295 pixels), i) 20% (i.e., 60 pixels) is related with the area/border of the two already cited dams, ii) 36% (i.e., 105 pixels) takes into account of pixels close to the coastline as well as to the rivers but outside the above mentioned zone and hence likely to be considered false positives, iii) the most of the remaining 44% (i.e., 130 pixels) of pixels is clustered in two sub-areas, clearly visible in Figure 12b, one is located between the mouth of the Bradano and Basento rivers and the other is on the left side of the Lato River. The first one was already identified as inundated by Reference [31] and [37], the latter, here identified for the first time, refers to the Castellaneta Marina village, where the freeway \"StradaStatale 106\" was closed due to the large presence of water [32; 33; 34; 35; 36]. Furthermore, it is worth mentioning that these two areas with an estimated extension of about 18.3 km\({}^{2}\), are not contemplated in the current flood risk map, suggesting a potential of satellite-based products even in terms of assessing (and possibly refining) such administrative instruments.  
The performance of the results improves when considering only the area within the black box, namely that mainly affected by the event. In particular, among the 172 pixels not included in the PAI area, 31 (i.e., 18%) are probably due to spurious effects, while the remaining 141 pixels (i.e., 82%) correspond to above-mentioned \"flooded for sure\" areas. Finally, 96% of the detected anomalies within the black box can be considered as real flooded area. This number decreases (i.e., 82%) accounting for the whole ROI, even if 36%, of the remaining 18%, is related with the borders of the San Giuliano and Monte Cotugno dams. Therefore, in absence of other information/documentation about other inundated zones within the ROI, only a residual possible 18% of false positives has been estimated, mostly related to the 7 December image. This achievement confirms the ALICE\({}_{\text{NDSI}}\) capability in flooded area detection with a high level of reliability.