## 3 Data and Methods
### Ancillary Data  
The reliability of the RST-FLOOD results has been assessed by means of a high resolution map, carried out applying a change detection scheme to a Landsat 7 (Enhanced Thematic Mapper Plus) ETM+ data (Figure 3) and the flood hazard maps provided, for the studied area, by the Italian Ministry of the Environment and Land Protection [43] (Figure 4). In addition, the sensitivity of the achieved outcomes has been evaluated for comparison with the outputs of the VIIIRS NOAA&GMU Flood Version 1.0 (VNG Flood V1.0, hereafter VNG) software, recently distributed in the framework of the CSPP network [44] (Figure 5). Two Landsat 7 ETM+ (scene of 2534 \(\times\) 3400 pixels, at 30 m of spatial resolution) images provided over the ROI with a higher spatial resolution then VIIIRS ones, have been used to evaluate the flood detection results. In detail, the Landsat 7 ETM+ images acquired on 5 December 2013, at 9.31 GMT and 24 December 2014, at 9.33 GMT were combined in a change detection scheme to highlight the flooded area. The Landsat Level-1 data, downloaded from USGS Earth Explorer Earth website [45], are distributed as scaled and calibrated digital numbers (DN). In this work, the DNs were converted to calibrated TOA (Top Of Atmosphere) reflectances using metadata which are distributed with the product. In Figure 3a,b the false colour composite images (R = Band 7, SWIR, 2.09-2.35 \(\upmu\)m; G = Band 5, SWIR, 1.55-1.75 \(\upmu\)m; B = Band 1, RED, 0.63-0.69 \(\upmu\)m) of the analysed imagery are shown. The 753 combination provides a \"natural-like\" rendition, where flooded areas should look very dark blue or black [46]. Looking at the images, the presence of a large number of blue pixels is evident for the one acquired concurrently with the 2013 flood event (Figure 3a), while the other should more reflect the unperturbed condition. Besides, for each image, three maps were produced: RED \(-\) SWIR (B3 \(-\) B5), RED/SWIR (B3/B5) and their normalized difference (NDSI = RED\(-\)SWIR, RED/SWIR, B3 \(-\) B5/B3 + B5), which all should be affected by a variation in surface water presence, as better discussed later (see Section 3.3). The \"water affected areas,\" shown in magenta in Figure 3c (re-projected at 375 m, for the comparison with RST-FLOOD results), is the \"and\" combination of the detections carried out integrating these three maps. By this approach, an area of about 24 km\({}^{2}\) has been estimated as flooded affected, mostly localized along the Basento, Bradano and Lato rivers. Such a value is likely underestimated because of a number of issues regarding Landsat data [47], like the presence of data gaps towards the edges of the images due to the striping caused by the failure of the Landsat-7 ETM+ scan line corrector (SLC) in 2003. In Italy, the Ministry of the Environment and Land Protection plans finances and controls the actions aimed at the hydrogeological risk reduction. In this framework, the Hydro-Geologic Safety Plan (named hereafter PAI) is drawn up for each river basin. In the Basilicata PAI, produced by the Basilicata Inter-Regional Basin Authority, through hydrological and hydraulic studies carried out by the University of Basilicata [48], three areas of fluvial pertinence in relation to flood risk as well as in relation to the natural water path have been defined as areas of probable flood risk [48]. Such zones are established according to the three following scenarios: i) frequently occurring flood events (high probability, likely return period 30-50 years); ii) less frequently occurring flood events (medium probability, likely return period 100-200 years); iii) extreme flood events (low probability, likely return period 300-500 years). The last ones, delivered by the Italian national geoportal [43] and updated at December 2016, are provided in Web Map Service (WMS) format. The PAI referring to the ROI is shown in Figure 4, where the lighter the colour (from black to yellow) the lower the probability of the occurrence of extreme floods.