## 6 Conclusions  
From the analysis of the data derived from the WR, TC, and IS, we deduced that, for the analyzed Etna eruption events, IR-PEW and TR-PEW anticipated the volcanic plume formation during the lava fountain at least one/two hours prior, while the radar was able to assess the increase in explosive activity, providing both \(H_{\mathit{TP}}\) and \(Q_{\text{M}}\) in near-real-time. In this analysis, we found that the different PEW1 combinations provided pre-alerts from \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Data**} & \multicolumn{6}{c}{**Lead Time \(\Delta t\) (min)**} \\ \cline{2-7}  & **IR-PEW1** & **IR-PEW2** & **IT-PEW1** & **IT-PEW2** & **TR-PEW1** & **TR-PEW2** \\ \hline
**2011-04-10** & \(117\) & NA & \(-34\) & \(18\) & \(141\) & NA \\ \hline
**2012-04-12** & \(140\) & \(63\) & \(-29\) & \(-65\) & \(169\) & \(128\) \\ \hline
**2013-11-23** & \(61\) & \(73\) & \(-27\) & \(21\) & \(88\) & \(52\) \\ \hline
**2015-12-03** & \(-37\) & NA & \(-54\) & NA & \(17\) & \(30\) \\ \hline
**2015-12-04** & \(108\) & \(-7\) & \(103\) & NA & \(5\) & NA \\ \hline
**2015-12-04** & \(796\) & \(7\) & \(784\) & \(2\) & \(12\) & \(5\) \\ \hline
**2015-12-05** & \(1909\) & NA & \(1888\) & \(-6\) & \(21\) & NA \\ \hline
**2021-02-16** & \(15\) & NA & \(23\) & NA & \(-8\) & NA \\ \hline
**2021-02-23** & \(106\) & \(33\) & \(-185\) & \(-24\) & \(291\) & \(57\) \\ \hline \hline \multirow{2}{*}{**Statistic (\%)**} & \multicolumn{6}{c}{**PosAlert**} \\ \cline{2-7}  & \(88.90\) & \(44.45\) & \(44.45\) & \(33.33\) & \(88.90\) & \(55.55\) \\ \cline{2-7}  & \multicolumn{6}{c}{**NegAlert**} \\ \cline{2-7}  & \(11.10\) & \(11.10\) & \(55.55\) & \(33.33\) & \(11.10\) & NA \\ \hline \multicolumn{7}{c}{**NotAlert**} \\ \cline{2-7}  & NA & \(44.45\) & NA & \(33.33\) & NA & \(44.45\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Lead times (minutes), \(\Delta t\)-PEW (1-2), for the considered Etna explosive events: infrasonic system (IS) with respect to the weather radar (WR) (IR_PEW), IS with respect to the thermal camera (TC) (IT_PEW), and TC with respect to the WR (TR_PEW) (upper part of the table). Statistics for each lead time, \(\Delta t\)-PEW (1-2), in terms of the positive alert (PosAlert), negative alert (NegAlert), and not detected alert (NotAlert), are presented (lower part of the table). NA stands for not available value. a few minutes to about 1 h before the occurrence of the paroxysmal phase, whereas the PEW2 combinations provided pre-alerts within about 1 h.  
In particular, the IR-PEW1 was confirmed as a valid pre-alert element, with a rate of 88.90% for positive warnings for the onset of explosive activity, identified as the Strombolian phase. Instead, the TR-PEW2 had a rate of 55.55%, and was suitable to detect the lava fountain phase. Moreover, the IT-PEW1 and IT-PEW2 combinations showed lower percentages of agreement. It should be noted that these results are from a first analysis of the developed approach, tested on a limited set of Etna eruptive events, which, therefore, need to be confirmed by a more exhaustive analysis on a greater number of paroxysms, also including additional sensors, to make the algorithm even more robust. The EW results obtained for Etna can be easily applied to other volcanoes where both IS and/or TC and WR co-exist. However, the appropriate thresholds need to be defined for the typical activities of the other volcanoes. In fact, our results indicated that the integration between IS and TC with WR can be efficiently used to define not only the onset of a volcanic eruption, but also to determine key ESPs. We can anticipate that the operational use of the IR-PEW or TR-PEW systems could change the way we monitor volcanoes and largely improve our early-warning systems and near-real-time forecasting in case of explosive eruptions. In addition, these cases provided key insights into the relationship between eruptive intensity, acoustic pressure, and image processing, and some cases may be consistent with a buoyancy-driven ascent for volcanic plumes.