## 5 Experimental Results  
The capability of the W1-M3A observing system to integrate underwater radioactivity and acoustic measurements into its already operational multidisciplinary payload was tested during Fall 2016 (from August to November). The wake-up intervals of UPAL were set to one minute when rain was detected, two minutes in case of mammal vocalization and seven minutes for idle mode. The acoustic data were processed by UPAL using the classification and quantification algorithms described in [32] and, in post-processing, the retrieved estimates of rainfall were cumulated hourly to be comparable with the other measurements acquired during the experiment. The KATERINA II sensor provided one spectrum every hour and two types of calculations were performed in an automated way: (a) gross gamma-ray rates were measured by summing the counts in the whole energy range (10-2700 keV) and dividing by the acquisition time in seconds (3600 s), and (b) counting rates in ROI obtained by summing the counts in the energy region of 351 keV for \({}^{214}\)Pb, 609 and 1764 keV for \({}^{214}\)Bi and dividing by the acquisition time. The quantification of the radioisotopes activity concentrations requires the analysis of the obtained spectra either manually using available software [33], or using dedicated automated algorithms [34]. Also, in order to obtain statistically acceptable results, given the short acquisition time (3600 s), grouping and summation of several spectra may be needed following appropriate analysis approaches [35]. Although quantification as well as association of activity concentrations with meteorological parameters are future tasks--out of the scope of the present work--for the sake of completeness, two typical gamma-ray spectra acquired during periods with and without rainfall are depicted in Figure 5. The first spectrum (depicted by dots)  
Figure 4: Sketch of the surface buoy of the W1-M3A observatory and images of the deployed sensors: the gamma-ray spectrometer at 6 m depth and the underwater passive aquatic listener close to the damping disk of the buoy at about 36 m depth. represents an indicative spectrum obtained during dry periods. The short acquisition time and the low activity concentration of radon progenies in the open sea, result to spectra of poor statistics, thus this spectrum was prepared by summing several hourly obtained spectra followed by appropriately time normalization. The spectrum depicted by the straight line was obtained during the storm on 10 of October 2016 with an acquisition time 3600 s. In the first one, the photo-peak corresponding to \({}^{40}\)K dominates, as potassium generates the enhanced continuum of Compton background in the range 10-1460 keV. Slight photopeaks attributed to radon progenies can be observed in the energy regions of 352 and 609 keV (\({}^{214}\)Pb and \({}^{214}\)Bi) attributed to background traces of lead and bismuth contained within the material of the station's structural frame. After a rainfall event, several photopeaks attributed to radon progenies can be observed. More specifically, photopeaks of \({}^{214}\)Pb are observed at the energies of 241, 270 and 351 keV and of \({}^{214}\)Bi at the energies of 609 and 1764 keV. The results from the automated analysis in the range of 352-609 keV are depicted in Figure 6 along with the total gamma-ray results (Figure 6b). The precipitation events as identified by the rain-gauge installed on the observatory and the hourly cumulative values provided by two C-band, dual-polarized weather radars positioned on Mount Settepani (Liguria Region) and Bric della Croce (Piedmont Region) at 1386 m and 736 m above sea level, respectively, are shown in Figure 6c. Observations from weather radars were selected as the closest pixel to the buoy of the regional mosaic (6.2-11.2\({}^{\circ}\) E; 46.0-46.6\({}^{\circ}\) N) with a spatial resolution of 800 m \(\times\) 800 m provided by the Environmental Protection Agency of Piedmont Region and Environmental Protection Agency of Liguria.