## 2 Related Works  
The chance of exploiting radio transmission in salt water was analyzed more than 50 years ago [9; 10; 11], underlining the severe attenuation that limited the usage of this technology to very few specific contexts. While the limited chances of exploiting EM waves for data transmission in salt water are well known, in the last years a number of application contexts emerged, where radio technologies may be exploited within the marine environment. Platforms like unmanned surface vehicles, water quality monitoring stations or structural health monitoring systems for infrastructures like harbors or bridges may exploit the radio channel for the transmission of collected data. Indeed, in several cases data is not required to be transmitted from high depths: for this reason, in the last years a limited number of contributions have emerged in the literature trying to analyze the usability of radio technologies in the presence of salt water. In this context, the Wireless Sensor Networks (WSNs) can be a promising tool for monitoring marine environments thanks to its strengths as the quasi real-time data transmission, the pervasive deployment, the scalability, the relatively low-cost and the unmanned operations [12]. In this regard, a new term has been coined to identify the IoT systems designed for underwater applications, the Internet of Underwater Things (IoUT). While a set of works focuses on the implementation of transmitters operating in the ELF to VLF bands [13], some others analyse the realization of tools operating at higher frequencies. Significant results were achieved in the High Frequency (HF) band: in [14] transmission in salt water was successfully achieved on field at a 1 MHz frequency, while in [15] frequencies up to 5 MHz were tested at distances up to 90 m. One of the techniques that have been employed to set up radio channels between partially submerged transmitters or receivers is the exploitation of lateral waves [16; 17]. In this case, short range successful transmission was also achieved at higher frequencies: in particular, in [17] also the 2.4 GHz band was tested, suggesting very short range transmission with common technologies like WiFi. An ad hoc antenna, to be employed under sea water to transmit at 2.4 GHz was also presented in [18]: 2.4 GHz transmission was also tested respectively in pools with commercial XBee modules in [19] and implementing ZigBee protocol in [20]. Despite these contributions, there is currently in the literature a lack of works analyzing the behavior in salt water of data transmission technologies operating at the so-called Sub-GHz frequencies, i.e., those frequencies below 1 GHz. These include a number of technologies like SigFox or NB-IoT that are playing a significant role in the spreading of IoT solutions. Due to its large diffusion, LoRa is the only technology whose usability in water has been partially analyzed. However, contributions only deal with fresh water [7; 8; 21; 22], with a single work proposing some tests in salt water [23]: nevertheless, these were carried out exploiting an ad hoc antenna and thus not setting up an actual LoRaWAN transmission channel. Therefore, to the best of our knowledge, this is the first work discussing the behavior of LoRaWAN technology in salt water. Demonstrating the applicability of these technologies to the marine context can facilitate the deployment of WSNs in manifold scenarios of interest for the scientific community, and in several cases quasi-superficial data transmissions are sufficient for the required task. It is the case of the structural health monitoring of bridges and harbors [24; 25], the supervising of the vital parameters of athletes during water sport training [26] and the monitoring of fish farms [27]. However, the presence of the human activities also has indirect implications in the modification of the aquatic habitats, for this reason other relevant research topics are those aimed at the monitoring of water quality [28], water pollution [29] and coral reef ecosystems [30].