## 3 Results  
### Etna Volcano  
Mt. Etna (37.748\({}^{\circ}\) N-14.999\({}^{\circ}\) E) is a stratovolcano located in Sicily (Italy) and represents one of the most active volcanoes in Europe. Gas/ash emissions, Strombolian activities, lava fountains and lava flows generally characterize its eruptive activity [31; 32]. Mt. Etna eruptions generally occur from summit craters (i.e., Voragine, Bocca Nuova, North East Crater, Southeast Crater and New Southeast Crater; [33], e.g., during 2011-2015, [34; 35; 36], as well as at the time of writing, intense paroxysms occurred; [37]), although some voluminous flank eruptions were also recorded in recent years (e.g., July-August 2001; October 2002-January 2003; September 2004-March 2005; May 2008-July 2009; [38; 39]). Figure 1 displays the temporal trend of hot pixels flagged by RASTer (red triangles) and AVA (green triangles) at Mt. Etna over the period 2000-2017 by analyzing an area of 10 km of radius centered around the summit crater. The plot shows that both RASTer and AVA considered the eruptive events of July 2001 as the most intense (see hot pixels number). In general, all the flank eruptions (see boxes in Figure 1) occurring during the investigated period were well detected by both systems. Figure 2 displays, for instance, the thermal anomaly maps generated by RASTer during some Mt. Etna flank eruptions. In particular, the daytime ASTER scene of 29 July 2001 (Figure 2a) shows how RASTer mapped the areas inundated by lava (see red and yellow pixels), indicating that the lava flow, moving in the south direction, extended up to about 1120 m elevation. Figure 2b displays the RASTer detection of 18 March 2014, showing a lava overflow from summit craters. In comparison with AVA, RASTer was capable of better mapping also less extended thermal anomalies (e.g., those associated with moderate Strombolian activities). Two examples are shown in Figure 3, displaying AVA and RASTer detections in reference to the Mt. Etna flank eruptions of 21 June 2008 and 27 October 2002. It is worth noting as RASTer was capable of mapping extensively and continuously (in the space domain) the main lava flows. Moreover, it correctly identified (on 27 October 2002, Figure 3b) some thermal anomalies that were not flagged at all by AVA (see crater area). Figure 1: Time series (2000–2017) of the daily number of hot pixels flagged by RASTer and AVA at Mt. Etna. Dotted black rectangles indicate the periods of Mt. Etna flank eruptions; these eruptive events show the highest daily number of hotspots. The intense explosive and effusive activity at the Southeast Crater is also highlighted in the period September–December 2006. Similarly, the birth and growth of the New Southeast Crater in 2011–2015 is shown on the right side of the diagram. Finally, a significant number of hotspots characterized Strombolian activity in 2017, mainly at the Voragine (VOR) and Bocca Nuova (BN) craters. The potential of RASTer in detecting subtle hotspots is emphasized in Figure 4, in reference to Strombolian activity of January-May 2020. The figure shows the identification of a thermal anomaly at the summit craters, where a Strombolian activity, gas-and-steam and ash emissions occurred since October 2019 ([[https://www.ct.ingv.it/](https://www.ct.ingv.it/)]([https://www.ct.ingv.it/](https://www.ct.ingv.it/)), multidisciplinary bulletins), becoming spatially more extended during February-early March 2020. Afterward, the number of hot pixels decreased, marking the reduction of thermal volcanic activity at the Voragine-Bocca Nuova (VOR-BN) complex (the former Central Crater of Mt. Etna). The comparison with information from field observations demonstrates the capacity of the RASTer system in monitoring the whole dynamic of Mt. Etna thermal activity, up to its lowest levels of intensity. Figure 2: Thermal anomalies detected by RASTer on ASTER scenes during the Mt. Etna flank eruptions of **(a)** 29 July 2001; **(b)** 18 March 2014. More intense TIR anomalies referring to pixels with \(\otimes_{TIR}(x,y,t)\geq 4\) are reported in red.