## 2 Related Works  
LoRaWAN is a MAC layer communication protocol based on the LoRa technology. As its name hints, LoRa is a long distance modulation that is able to reach coverage ranges up to few kilometers in urban areas and up to tens in rural environments. Either the LoRa modulation and the LoRaWAN protocol were deeply dissected within a thorough survey [16] by firstly presenting both LoRa and LoRaWAN and then by comparing and reviewing a conspicuous amount of related references that were published within the last three years beforehand the publication of this survey. Finally, the study in Reference [16] also points out possible improvements and open challenges that could be faced by making use of these two technologies. Several papers have already presented various solutions exploiting LoRa networks deployed in as much application scenarios testing sundry performances [17; 18; 19] (e.g., transmission distances, energy consumption, reliability, packets collision and so on). Some of these studies will be reported hereinafter focusing on the ones reporting long LoRa links for networks employed in severe contexts. However, LoRa transmission over seawater is a hot research topic at the moment hence the literature is still lacking. The concept of harsh environment encloses plenty of case studies and industrial plants are one of these. Such a framework was treated in Reference [9] where a LoRa sensor node for fault detection of chemical emissions was implemented. For the sake of simplicity, sensor node wireless coverage was not actually tested within a plant. Hence, it was validated indoor within a structure that can be compared with an industrial plant due to its size and morphological characteristics. Indeed, it is a five floor building having a rectangular shape whose sides are 70 m and 100 m each enclosing a total surface of 7.000 m\({}^{2}\) per floor. Moreover, each of them hosts many rooms separated by large concrete walls up to 1 m of width. Rooms are employed as scientific laboratories containing miscellaneous electromagnetic instrumentation. In addition, the entire building is fully covered with WiFi networks for Internet connection. Thus, this test-bed may be categorized as a harsh one due to both the elevated level of electromagnetic noise and the dense presence of obstacles. Performances, in particular data loss rates, were satisfactory even if a worst case scenario was set up since the receiver was placed in a corner of the third floor and the transmitter was tested at several spots, some of them were the opposite corners with respect to the receiver, across the five storeys. Therefore, the outcome of such a study suggested that comparable performances could have been reached in Line of Sight (LoS) conditions as this paper test scenario entails. Some tests of LoRa links over urban and rural environments are reported within the conference paper [20] and the relative results, in terms of covered distance, are comparable with the ones presented in this paper. However, trial settings differ from those that will be listed in Section 5. The most important one is the application scenario: even though there are usually no large obstacles (e.g., buildings or mountains) offshore, transmissions over the sea are especially a tough challenge since seawater behaves as a huge ground plane thus causing odd reflection phenomena. Another dissimilarity resides in antennas installation, since those used in this work were positioned lower than that of Reference [20], and a further one is represented by different employed transmission parameters. As it will be reported later on (see Section 5), in this paper six Spreading Factors (SFs)were tested rather than only one as the authors of Reference [20] did, even if with a lower number of broadcast packets. Continuing with dense urban contexts, in a previous work [3] the authors of this paper developed a LoRa sensor node prototype for the remote sensing of the filling level of trash bins.