## 4 Sensors Integration into the W1-M3A Monitoring System  
The software embedded in the controller of the W1-M3A observatory has been fully developed by the research group of the National Research Council of Italy who takes care of the technological and scientific development of the platform in such a way that innovative sensors can be integrated straightforward into the platform after all needed software and hardware interfaces have been developed. As soon as the executable program starts, the controller gets several parameters of configuration from an initialization file stored locally: the calibration coefficients of the sensors, the duration of the duty cycle, the scheduled start-up time or period for each instruments or group of homogenous of sensors, the sampling frequency for each input analogue channel and the parameters related to the data transmission (i.e., frequency of outgoing call, allowed phone numbers of the receiving station ashorse, maximum number of files that can be transmitted for each call, etc.). Once the configuration phase is completed, the program operates uninterruptedly. Although each mentioned parameter can be configured by users for special purposes, the normal operating mode consists of a duty cycle of one hour. In order to guarantee the full integration of the KATERINA II and UPAL sensors into the observation system a specific flow of actions has been defined to guarantee synchronization between spectroscopy data, acoustics samples and all other ancillary measurements based on the reference timing obtained by the GPS onboard the platform (Figure 3). Specifically, the KATERINA II system was set up to acquire one spectrum per hour in sequential mode. At the end of a duty cycle, that is the time instant of enablement of a new acquisition period, the controller initiates the sampling of all meteorological instruments and sends the starting command to the KATERINA II. One hour later, the controller instantaneously interrupts the acquisition of the whole on-board instrumental payload to perform calculations of statistical analysis on meteorological observations and to retrieve the hourly cumulative gamma-ray spectrum. Subsequently, the controller deletes the data saved on the internal memory of the gamma-ray spectrometer and initiate the repetition of the whole acquisition process. The time latency between the end of one acquisition period and the beginning of the next one is less than 10 s. As soon as a gamma-ray spectrum is retrieved, an automated routine (running in parallel with the acquisition), decodes the hexadecimal output of the sensor, translates the output into string, selects the values of the channels corresponding to ROIs of \({}^{214}\)Pb, \({}^{214}\)Bi, \({}^{40}\)K, \({}^{208}\)Tl and integrates them in the dataflow of the W1-M3A system to be transmitted ashorse, whereas the full spectra is saved on the onboard compact flash memory. Since UPAL uses an adaptive sampling strategy and does not allow a polling mode during operation, a listening subroutine was developed. As soon as a new message is made available by UPAL, it is transmitted to the main controller of the buoy through RS232. This information is then included in the main data stream of the buoy and transmitted ashorse with a reference time for each acquisition. As regards the physical installation, the KATERINA II unit was clamped to the main body of the observatory and close to the surface (at 6 m depth) in order to monitor the variations of \({}^{222}\)Rn progenies concentration. Its two cables (one for the bidirectional communication and one for the power supply) were fixed along the body of the buoy up to the microcontroller, housed in the small laboratory on the top of the platform. Similarly, UPAL was clamped at the maximum available depth of the observatory (36 m) in order to provide acoustic information with a footprint on sea surface of about 100 m [31]. The depth of installation of UPAL was free from acoustic interferences due to the oceanographic payloads of the observatory.