## 3 Results and Discussion
### The Experimental Campaign of Stromboli Volcano
Although promising in terms of cost saving and speed, our measurements were slightly different from the ones acquired by the UV camera [41] and affected by a high uncertainty level due to the presence of wind blowing in the perpendicular direction, with respect to the system location, the worst observing condition for the tracking of the wind [40]. Nonetheless, they were found in agreement, within the error bar, with weather data acquired by conventional devices and with a precision comparable to that of stand-alone fixed-beam correlation lidars. It should be noted that, a comprehensive comparison with local data was considered unreliable, since the nearest weather station on the island performed 6-h average of weather parameters acquired at 4 m ASL and not at the same height of the laser beam pointing. For these reasons, efforts will have to be devoted to advance the configuration of BILLI (e.g., implementing at least three beams or a 360-degree scanning mirror) to fully and accurately retrieve the three components (x, y, and z) of the wind velocity [40]. Therefore, due to the constraints (in terms of dataset duration and results reliability) of our preliminary tests on the fast tracking of wind velocity, during the Stromboli campaign, CO\({}_{2}\) flux time-series were retrieved using v\({}_{\text{p}}\) values obtained from processing the sequences of UV camera images [41]. Once having obtained the CO\({}_{2}\) dispersion maps and the plume transport velocity using the method described in Section 2.2.4, it was possible to retrieve the CO\({}_{2}\) flux time-series with a cumulative uncertainty equal to 25% (dominated by the integration area uncertainty), as reported in Figure 4b [41]. The results confined the CO\({}_{2}\) flux during 24-29 June 2015 in the range from \(1.8\pm 0.5\) to \(32.1\pm 8.0\) Kg/s. The daily mean values of CO\({}_{2}\) flux were obtained by averaging all successful results for each measurement day. The values range from \(8.3\pm 2.1\) (24 June) to \(18.1\pm 4.5\) (25 June) Kg/s and corresponded to daily emissions of 718 and 1565 tons, in that order. These data are in agreement with past carbon dioxide estimates carried out at Stromboli. Moreover, in Figure 4b, our lidar-based CO\({}_{2}\) fluxes were compared with alternative measurements, obtained by multiplying the CO\({}_{2}\)/SO\({}_{2}\) ratio by the SO\({}_{2}\) flux, which is obtained using the traditional Multi-GAS + UV spectroscopy-based techniques. Despite the issues of the Multi-GAS + SO\({}_{2}\) flux approach reported in the literature (distinct temporal resolutions, and poor temporal alignment [41]), we found a general agreement between the CO\({}_{2}\) fluxes obtained by BILLI and the usual instruments. This provided reciprocal trust for both techniques. Furthermore, BILLI-based carbon dioxide fluxes showed a better temporal resolution (\(\approx\)16-33 min) and greater continuity. Moreover, BILLI as well as other standoff instruments, is intrinsically safe for operators [41]. In conclusion, although several improvements were made (higher distances reached, fully automated operational routines, independent measurements of plume transport velocity) with respect to the previous campaigns [39; 40; 41], efforts were needed to improve the system (in particular, improving portability and reducing power requirements). At the same time, further in-field tests were still necessary to fully explore the potential of our system, validating the reliability and efficiency of the data analysis method.