LoRa-Based Wireless Sensors Network for Rockfall and Landslide Monitoring: A Case Study in Pantelleria Island with Portable LoRaWAN Access

: Rockfalls and landslides are hazards triggered from geomorphological and climatic factors other than human interaction. The economic and social impacts are not negligible, therefore the topic has become an important ﬁeld in the application of remote monitoring. Wireless sensor networks (WSNs) are particularly suited for the deployment of such systems, thanks to the different technologies and topologies that are evolving nowadays. Among these, LoRa modulation technique represents a ﬁtting technical solution for nodes communication in a WSN. In this paper, a smart autonomous LoRa-based rockfall and landslide monitoring system is presented. The structure has been operating in Pantelleria Island, Sicily, Italy. The sensing elements are disposed in sensor nodes arranged in a star topology. Network access to the LoRaWAN and the Internet is provided through gateways using a portable, solar powered device assembly. A system overview concerning both hardware and functionality of the nodes and gateways devices, then a power analysis is reported, and a monthly recorded result is presented, with related discussion.


Introduction
Landslides and rockfalls are natural hazards linked to the combination of geomorphological and climatic factors in response to triggering mechanisms, such as heavy rainfall or seismic events, vegetation interaction, and human action [1,2]. Due to the rising awareness of economic and social impacts of landslides and rockfalls, the risk control of these events has become a topic of major interest. The effects include economic losses, the threat to human safety, environmental endangerment and impact on the possibility of urbanization [3]. A clear example about the danger of these occurrences is shown by events in combination with transport routes [4], where in addition to damages to infrastructures, there are unfortunately monetary losses due to the service disruption. The interest of the scientific community in the major hazards of these phenomena is well known worldwide, especially in areas where the presence of rock formations or unstable terrains represent a high source of risk [5].
The island of Pantelleria, located between the coasts of southern Sicily (Italy) and Tunisia, represents the emerged part of a volcanic structure. The structure of this island is deforming due to volcanic and tectonic activity [6]. It is necessary to monitor the rockfall and landslide activity along the surfaces of slopes and rock faces for safety purposes and to track the degradation and change of the territory. The morphology of the rocky walls in Pantelleria, especially along coastal areas, makes the development of a wired structural monitoring system difficult. Wireless sensors networks offer an advantageous mechanism for monitoring purposes because it is possible to implement a network of nodes without wiring, and to use sensing units to gather information. Earlier, engineers have employed wired and single-hop wireless data acquisition systems to acquire useful data for structural monitoring [7,8]. However, power and wiring constraints can combine in increasing the cost and complexity of data acquisition, most importantly by limiting the number and applicable location of sensor nodes. Maintenance and deployment costs can be increased too. Considering these, wireless sensor networks can often help address these issues.
The current trend is to embrace Internet of Things (IoT) paradigms, benefiting from smart nodes to build flexible and powerful infrastructures for data acquisition and analysis. The physical devices equipped with sensing instrumentation are connected to the internet, which allows data exchange between heterogeneous platforms, making the system technology independent from a certain point of the acquisition chain.
In the recent years WSNs have reported a rapid growth thanks to various new technologies for wireless communication, new implementations of ad-hoc hardware devices, and important academic and industrial research effort in this matter [9]. The applications served by wireless networks are various and different [10], including environmental monitoring [11], health related applications, including wearable systems [12], early warning tools [13], and industrial control [14].

Overview on State of the Art Rockfall and Landslide Monitoring Systems
The development of an optimal solution for a monitoring system is an open challenge for different reasons. Determining which of the existing ones is the most appropriate solution is absolutely not trivial. The sensing structures are incredibly heterogeneous in many terms: technology, topology, reliability, cost, and complexity. For the aforementioned reason, it is challenging to find a system that fits them all indiscriminately. Furthermore, due to the multidisciplinary nature of the monitoring topic, taking into account all the variables involved is complicated.
In this section, different solutions for rockfall and landslide monitoring systems, based on wired and wireless networks will be briefly reviewed, so to give a perspective on the state of the art. Employing structural health monitoring (SHM), a connected aspect of the aforementioned phenomena, an overview on WSN-based applications will be reported.
In [15] the authors present a survey of technological developments and research work in the IoT, applied to the prevention of geological hazards. It surveys the applications in the monitoring and early warning of various types of common geohazards: rockfall, surface collapse landslides, and debris flow earthquakes. Some IoT-providing technologies are investigated in geohazards, and the challenges are summarized with an address to future developments in the topic.
Wireless sensor nodes incorporating microelectromechanical system (MEMS) inertial measurement unit (IMU) sensors can be used to detect movements on rock or soil slopes. In [16] the authors present a sensing system able to recognize a rock fall event and to monitor the structural parameters of a protection barrier, which can be a gabion mesh or concrete blocks. The architecture is modular, organized with a control unit and sensing nodes disposed on the installation site. With these devices, information about the vibration and the inclination of the falling rock protection barrier is gathered. The data are collected on a web server which handles recording and automatic messages in case of criticisms. A web application has been developed to create summary reports and to analyze the data collected. The system is currently working on a gabion mesh located in the southern part of Italy.
Despite the ability of the IMU-based WSNs to measure accelerations and rotations, there is a significant research effort to describe and distinguish different types of slope movement. Studies have presented distinct patterns of accelerometer data in physical structures' behavior [17]. The concept of pattern recognition has been utilized in experimental studies that were carried out by the authors using the accelerometer and gyroscope readings to classify movements. This information serves as the fundamental understanding of a landslide in civil engineering, as well as helping in analyzing the stability of the slope and the implementation of safety and mitigation structures. In [18], the authors present a system based on WSN nodes which communicate with a central station using 802.11 g standard [19]. The station is a trailer equipped with computers for onsite data analysis and cellular uplink. The connection is used for internet communication to a central storage server. Experiments using a rock equipped with a sensor device are carried out and results reported to show the different IMU data for possible movements of the mass. In [20], the authors propose a system based on acoustic emission or microseismic monitoring to provide an insight into stress and strain conditions in the subsurface rock mass. Detecting microseismic events originating from an unstable rock mass is important for locating growing cracks and to analyze the triggering mechanisms of possible future collapses. In [21], a network of sensor nodes based on MEMS analog output accelerometers and MicaZ [22] mote hardware is deployed. Each node is equipped with a microcontroller and a 2.4 GHz transceiver. The devices are mounted in a linear configuration along the Golden Gate Bridge, which makes the multi-hop transmission topology particularly suited for the study. Effort is made to analyze the data transmission reliability in pipeline mode to reduce data loss. The mechanism implemented is as follows: the sender transmits the data when it is requested by the receiver, and the receiver identifies possible missing packets and returns a list back to the sender, which resends those until total reception is achieved. A cycle of data sampling and collection is executed in about 9 h and produces 20 MB of data.
In [23], a disaster prevention system tested in a slope area around Taiwan is shown. Monitoring equipment was installed on the protection structure construction to display quantitative data of rockfall events. The accelerometric nodes prototypes are built on commercially available electronic circuits encapsulated in plastic enclosures and are three different types, each one characterized by a different transmission technology. The first is a long range (LoRa) [24,25]-based node, the second uses narrowband-IoT (NB-IoT) [26] and the third communicates with Long Term Evolution (LTE) M1 [27,28]. The LoRa unit does not use a free access media access control (MAC) layer but communicates data to a Raspberry Pi 3B [29] unit which uses Wi-Fi to later transmit to a MySQL [30] server. There is also a wired vibration gauge, VB-200SC [31], interfaced through RS-485 [32] with an IoT gateway to transmit data over Wi-Fi. In [33], the authors implement a LoRa-based WSN on an uninhabited hillside landslide, studying the feasibility of a LoRa-based network in harsh environments and focusing on the zone coverage of the communication and on received signal strength intensity (RSSI)-based triangulation to localize a particular node in the network. However, we do not find an in-depth description on the hardware implementation of the sensor node, a description of the mounting mechanisms on the slope side, or power-related features of the elements. In [34] the authors propose a landslide-monitoring-method-based LoRa network and intelligent sensing for rainfall and landslide displacement in Shuicheng County, Guizhou Province, China. The general structure, hardware, and software design of the system are described comprehensively. The work reports the possibility, for the nodes, to operate in normal or reduced power mode to obtain a lower current absorption of 1 mA.
An application of a LoRa-based wireless monitoring device for SHM is presented in [35]. In a smart city, Remote Structural Health Monitoring (RSHM) is a perfect solution for tracking critical damage to urban structures. The cited paper proposes TenSense M30, an IoT sensor node to enable wide communication coverage, with a long battery duration, for monitoring the health of bolted joints. TenSense M30 has a footprint that can be used as an add-on to current structures. Hardware and mechanical tests are presented.
In this work a low-cost autonomous LoRa-based rockfall and landslide monitoring system, operating in Pantelleria Island since May 2022, is presented. The sensor nodes are independent elements in a star topology network with the LoRaWAN [36,37] gateway, making the network more robust in case of node malfunction. The access to the internet layer is provided using a compact, portable, solar-powered gateway implementation system. This paper is structured as follows: a system overview is given, with a functionality description. The next section describes the nodes and gateway assembly box with electrical measurements of power performances of the nodes and considerations on its long-term reliability. A section with a month's recorded data is reported. Finally, conclusions are drawn.

System Overview
In IoT-oriented WSNs, it can be beneficial to implement low power wide area network (LPWAN) technologies. This can allow for good energetic performances of the sensor nodes, which is crucial in energy harvesting powered devices [38][39][40]. Using the emerging LPWAN technologies, an overall inexpensive implementation is achievable [41,42]. In these structures, especially for monitoring purposes, the required data rate is usually lower than high-speed telecommunications applications, such as large file transfers or video streaming. LPWAN are often used in scenarios where a small amount of data is transmitted at intervals of time [43], often leading to less complicated transceiver hardware, hence reduced costs. The MAC layer deployment often comes with the highest costs of the whole system [44], so if a relatively unexpensive solution is provided with respect to the total cost of the system, an optimal point is reached. The LoRaWAN MAC layer, regulated by the LoRa Alliance [45], provides this kind of performance, being a free network protocol accessible by dedicated LoRaWAN gateways. These devices can be found commercially at affordable prices in certificated outdoor models. Such elements can be interfaced with free web services to create a reliable, fully developed, low-cost network, as will be presented later in this paper. The network architecture (see Figure 1), in the aforementioned MAC layer, is organized in a star structure with the gateway acting as the star center. The nodes communicate with a single hop connection using LoRa modulation, which is a chirp spreading spectrum (CSS)-based technique from Semtech, as mentioned in the introduction. term reliability. A section with a month's recorded data is reported. Finally, are drawn.

System Overview
In IoT-oriented WSNs, it can be beneficial to implement low power wid work (LPWAN) technologies. This can allow for good energetic performances sor nodes, which is crucial in energy harvesting powered devices [38][39][40] emerging LPWAN technologies, an overall inexpensive implementation is [41,42]. In these structures, especially for monitoring purposes, the required usually lower than high-speed telecommunications applications, such as larg fers or video streaming. LPWAN are often used in scenarios where a small amo is transmitted at intervals of time [43], often leading to less complicated transc ware, hence reduced costs. The MAC layer deployment often comes with the h of the whole system [44], so if a relatively unexpensive solution is provided w to the total cost of the system, an optimal point is reached. The LoRaWAN M regulated by the LoRa Alliance [45], provides this kind of performance, being work protocol accessible by dedicated LoRaWAN gateways. These devices ca commercially at affordable prices in certificated outdoor models. Such elem interfaced with free web services to create a reliable, fully developed, low-co as will be presented later in this paper. The network architecture (see Figur aforementioned MAC layer, is organized in a star structure with the gateway a star center. The nodes communicate with a single hop connection using LoRa m which is a chirp spreading spectrum (CSS)-based technique from Semtech, as in the introduction. In [46] an energetic efficiency comparison between LPWAN IoT devices LoRa has similar power performances to SigFox [47], which does not allow a plementation at access layer, as it is LoRaWAN. In [48] we can find how this compares with other IoT-oriented transmission technologies, also reporting g age when working in poor link conditions.
The system proposed in this work is as follows: sensor nodes are equ MEMS accelerometer, GPS unit for tracking, gas sensor measuring relative hum ometric pressure, ambient temperature, and gas resistance which can be used ity (AQI) index. The nodes transmit packets of 38 bytes size every 60 min to t through LoRa physical layer. This last element is connected to the internet v using LTE by means of a subscriber identity module (SIM), and powered vi vesting by means of a solar panel and charge storage battery. A detailed ha scription will be provided in the next section. The packets received at the g In [46] an energetic efficiency comparison between LPWAN IoT devices is available. LoRa has similar power performances to SigFox [47], which does not allow an easier implementation at access layer, as it is LoRaWAN. In [48] we can find how this modulation compares with other IoT-oriented transmission technologies, also reporting good coverage when working in poor link conditions.
The system proposed in this work is as follows: sensor nodes are equipped with MEMS accelerometer, GPS unit for tracking, gas sensor measuring relative humidity, barometric pressure, ambient temperature, and gas resistance which can be used for air quality (AQI) index. The nodes transmit packets of 38 bytes size every 60 min to the gateway through LoRa physical layer. This last element is connected to the internet via IPv4 [49] using LTE by means of a subscriber identity module (SIM), and powered via solar harvesting by means of a solar panel and charge storage battery. A detailed hardware description will be provided in the next section. The packets received at the gateway are managed through The Things Network [50] service, where, using a payload decoding function, the incoming bytes are encapsulated into a JavaScript Object Notation (JSON) object for data exchange between websites. The object has a key-value field and numerical value for each measured quantity. HyperText Transfer Protocol (HTTP) integration is used to send the packets to the Losant IoT [51] website, which acts as a user frontend, database, and alert-triggering service. In this service the obtained data is plotted into a user dashboard and stored into a database, which is accessible from the monitoring system provider for data analysis. In Figure 2, the application specific block scheme is shown. Each node of the WSN is installed on the barrier along the steel braided cables (Figure 3), fixed with steel clamps. function, the incoming bytes are encapsulated into a JavaScript Object Notation (JS object for data exchange between websites. The object has a key-value field and nume value for each measured quantity. HyperText Transfer Protocol (HTTP) integratio used to send the packets to the Losant IoT [51] website, which acts as a user front database, and alert-triggering service. In this service the obtained data is plotted in user dashboard and stored into a database, which is accessible from the monitoring tem provider for data analysis. In Figure 2, the application specific block scheme is sho Each node of the WSN is installed on the barrier along the steel braided cables (Figur fixed with steel clamps.  With the nodes placed at different heights and positions, the LoRa connectivi provided with two gateways at different locations to enable all the 12 sensing devic have radio communication. The gateways are placed in a position where the LTE con tion is achievable, as the cellular connection in the island is not accessible everywhere where sunlight is available during a good portion of daytime ( Figure 4). managed through The Things Network [50] service, where, using a payload decoding function, the incoming bytes are encapsulated into a JavaScript Object Notation (JSON) object for data exchange between websites. The object has a key-value field and numerical value for each measured quantity. HyperText Transfer Protocol (HTTP) integration is used to send the packets to the Losant IoT [51] website, which acts as a user frontend, database, and alert-triggering service. In this service the obtained data is plotted into a user dashboard and stored into a database, which is accessible from the monitoring system provider for data analysis. In Figure 2, the application specific block scheme is shown. Each node of the WSN is installed on the barrier along the steel braided cables (Figure 3), fixed with steel clamps. With the nodes placed at different heights and positions, the LoRa connectivity is provided with two gateways at different locations to enable all the 12 sensing devices to have radio communication. The gateways are placed in a position where the LTE connection is achievable, as the cellular connection in the island is not accessible everywhere, and where sunlight is available during a good portion of daytime ( Figure 4).

Hardware Structure
In this section the hardware of the sensor nodes and gateways will be described. An analysis of power consumption is reported.

Hardware Structure
In this section the hardware of the sensor nodes and gateways will be described. An analysis of power consumption is reported.

Sensor Node Structure and Power Analysis
The nodes are electronic circuits composed of a co-ordinator microcontroller, movement and environmental sensors, global positioning system (GPS) modem, an UART to USB interface, battery management unit connected to a 5 V solar panel, and a power supply and distribution chain. The microcontroller is a STM32L [52] from STMicroelectronics, 32-bit ARM Cortex M3-based, specified for low power applications. The low-power run mode of this microcontroller unit (MCU) with few microamperes specified makes it particularly suitable to battery powered applications, hence harvesting-based WSNs. The chip is equipped with multiple universal asynchronous receiver-transmitter (UART) channels, two different serial peripheral interface (SPI) ports, and two inter-integrated circuit (I 2 C) interfaces. In phase of debug and programming, it is possible to use a universal serial bus (USB) 2.0 compliant interface by means of a CP2102 UART to USB circuit from Silicon Labs [53]. This device works with COM communication port computer applications and is powered by the USB bus at 5 V, accessible at the micro-USB connector. The battery is a 3700 mAh lithium polymer (LiPo) battery. The voltage is readable using the analog to digital converter (ADC) of the microcontroller. The cell is charged using solar harvesting or directly from the USB port by means of a BQ21040 [54] single cell charging integrated circuit from Texas Instruments (TI). It is packaged in a SOT-23 case and supports a charge current up to 0.8 A at 4.2 V charging voltage. Thermal protection needs an external NTC resistor on the battery case to protect in case of excessive battery temperature. Most of the circuits in the sensor node are powered at 3.3 V by means of a RP104N331 [55] low drop-out (LDO) regulator by Nisshinbo. The GPS modem onboard is a Ublox MAX-7Q [56], powered at 3.3 V, switched using a TI TPS27082 [57] load switch. It communicates with the MCU using UART. The movement sensor is a MEMS based digital output three-axis accelerometer mode LIS3DH [58] from STMicroelectronics, supporting low power mode with a current consumption of around 2 µA. The chip is interfaced with the microcontroller by I 2 C and supplied at 3.3 V.
The LoRa module is SX1276 [59] from Semtech, a transceiver for long-range technology that implements the spread spectrum communication patented by Semtech. It is interfaced with the microcontroller using SPI and supplied at 3.3 V. SX1276 can achieve a sensitivity of over −148 dBm using a low-cost crystal, moreover this integrated circuit is available on the market at a reduced cost. The unit is operating at transmission (TX) power of 13 dBm. To enable radio communication, an 868 MHz ISM band planar dipole antenna model PIOV008NRAA-100 [60], from Amphenol, is connected to the wireless module by a U.FL surface mount connector. The operating temperature of the nodes ranges from −40 • C to +85 • C. The barometric pressure is kept at the same value of external ambient, thanks to a compensation valve. In Figure 5, the sensor node block scheme is reported.
The node operates in sequential operation. At first, the device is in standby mode; this means that the onboard circuits are put in low power mode to enable reduced current absorption. At fixed time intervals selectable by the user, there is standby deactivation, and a data acquisition procedure begins. GPS position fetching is the initial procedure. If the GPS signal is not found until 30 s timeout reaching, other satellite connections are attempted, otherwise the node proceeds with sensor reading. Data from the movement sensor and environmental unit are retrieved, after which a data transmission phase begins, using LoRa interface. After data sending is concluded, the node will return to low power mode. If the LoRa network is not accessible in the sending phase, after a count of eight tries at gateway connection, the node will return to standby mode until next data sending scheduled interval. This procedure is valid for all the sensor nodes in the WSN. a U.FL surface mount connector. The operating temperature of the nodes range −40 °C to +85 °C. The barometric pressure is kept at the same value of external am thanks to a compensation valve. In Figure 5, the sensor node block scheme is repo The node operates in sequential operation. At first, the device is in standby this means that the onboard circuits are put in low power mode to enable reduced absorption. At fixed time intervals selectable by the user, there is standby deact and a data acquisition procedure begins. GPS position fetching is the initial proce the GPS signal is not found until 30 s timeout reaching, other satellite connecti attempted, otherwise the node proceeds with sensor reading. Data from the mo sensor and environmental unit are retrieved, after which a data transmission phase using LoRa interface. After data sending is concluded, the node will return to low mode. If the LoRa network is not accessible in the sending phase, after a count o tries at gateway connection, the node will return to standby mode until next data s scheduled interval. This procedure is valid for all the sensor nodes in the WSN.
In Figure 6 a flow diagram of the nodes' operation is reported with the afo tioned operating stages pictured. The power on represents the moment when pow ply is connected, followed by the first initialization which is executed only afte reset or power on.
Power consumption of the sensor nodes is relevant to battery duration, it is th necessary to reduce current absorption during low power mode to ensure energet ciency. Measurements were carried out to check the power draw of the node u ultra-precise current monitor setup based on INA229 [61], from TI. The integrated is interfaced using SPI, with a microcontroller model SAMD21 from Microchip [62 to manage the readout and to communicate the data towards a personal compute the COM port. The sensor node is put in series with a shunt resistor selected to r absorbed current Inode, that represents the current drawn from the LiPo battery. A matic of the setup is reported in Figure 7. In Figure 6 a flow diagram of the nodes' operation is reported with the aforementioned operating stages pictured. The power on represents the moment when power supply is connected, followed by the first initialization which is executed only after every reset or power on.   In Figure 8, a graph reporting the current absorption in mA (vertical axis) during data Power consumption of the sensor nodes is relevant to battery duration, it is therefore necessary to reduce current absorption during low power mode to ensure energetic sufficiency. Measurements were carried out to check the power draw of the node using an ultra-precise current monitor setup based on INA229 [61], from TI. The integrated circuit is interfaced using SPI, with a microcontroller model SAMD21 from Microchip [62], used to manage the readout and to communicate the data towards a personal computer using the COM port. The sensor node is put in series with a shunt resistor selected to read the absorbed current I node , that represents the current drawn from the LiPo battery. A schematic of the setup is reported in Figure 7.  In Figure 8, a graph reporting the current absorption in mA (vertical axis) during data sending attempts is reported over a time interval of 50 s (horizontal axis) at 3.8 V battery voltage. The node will not reach a gateway, therefore several connection efforts are attempted. It operates at an average active current of 35.7 mA, following which is the standby mode activation, where the current absorption drops to an average value of ILP = 16 µ A. In Figure 8, it is also possible to observe the current peaks due to transmission attempts.  In Figure 8, a graph reporting the current absorption in mA (vertical axis) during data sending attempts is reported over a time interval of 50 s (horizontal axis) at 3.8 V battery voltage. The node will not reach a gateway, therefore several connection efforts are attempted. It operates at an average active current of 35.7 mA, following which is the standby mode activation, where the current absorption drops to an average value of I LP = 16 µA. In Figure 8, it is also possible to observe the current peaks due to transmission attempts.  In Figure 8, a graph reporting the current absorption in mA (vertical axis) during data sending attempts is reported over a time interval of 50 s (horizontal axis) at 3.8 V battery voltage. The node will not reach a gateway, therefore several connection efforts are attempted. It operates at an average active current of 35.7 mA, following which is the standby mode activation, where the current absorption drops to an average value of ILP = 16 µ A. In Figure 8, it is also possible to observe the current peaks due to transmission attempts.  The total duration of one acquisition cycle is 60 min long, during a successful attempt of wake-up, GPS data retrieving and LoRa transmission, in case of satellite reachability, for a time span of about T ACT = 15 s. This estimates a low power operation mode of 3585 s over one activity cycle. The average current absorption maintains at I ACT = 35.7 mA, being the LoRa transceiver and GPS unit absorption peaks, which are very narrow in time. The single 1 h cycle battery discharge due to the activity is given by: The discharge in one cycle due to the low power mode is the following, where T LP is the sleep time per cycle that is 45 s: C LP = (T LP · I LP )/3600 = 0.0002 mAh (2) One day of operation, multiplying the total discharge of one cycle by 24, gives a discharge of about 3.56 mAh. In one year of operation, multiplying the daily discharge by 365 days, there is a discharge of about C Y = 1300 mAh. This results in a total battery duration, in case of an ideal steady battery state, of around 2.8 years in case of total darkness where solar harvesting is not working. For the node-obtained data that will be illustrated in the sequent section, the battery remains almost fully charged for all the working time, thanks to the solar panel implementation, which gives the sensor nodes a sufficient level of energy.

Gateway Assembly
The two LoRaWAN gateways provide access to the internet layer through The Things Network service, as described above. The gateways are mode UG65 [63] from Milesight, powered at 12 V direct current (DC) using a valve-regulated lead-acid battery. It is based on a 64-bit 1.5 GHz ARM Cortex A53 processor, supported by 512 MB of DDR4 RAM and a flash memory of 8 GB. It supports external and internal antennas, with an output power at the output stage for LoRaWAN of 27 dBm and a sensitivity of −140 dBm. The working band is EU868 which stands for European band, with acenter frequency of 868 MHz. The LTE-interfaced gateways are assembled in a waterproof IP65 enclosure with the supply system. The rated typical total power of the gateway is 2.9 W. The operating temperature range of the gateways is −40 • C to +70 • C.
The solar panel is a IP65 polycrystalline type, model NX30P from Energiasolare100 [64], with 344 mm length, 645 mm width and 25 mm height. The weight is 2.4 kg for the whole package in aluminum frame. The peak power is 30 W, and it reports an open circuit voltage of around 21 V. The battery charge regulator is an EP5 [65] model PWM-based device. It features overcurrent and reverse polarity protection, working at 13.8 V battery charge, retaining voltage. The storage is implemented using a PCA12-12 [66] battery from Prime, which powers the LoRaWAN gateway through a DC jack. In Figure 9, the gateway mounting scheme is reported.
in the sequent section, the battery remains almost fully charged for all the working thanks to the solar panel implementation, which gives the sensor nodes a sufficient of energy.

Gateway Assembly
The two LoRaWAN gateways provide access to the internet layer through Things Network service, as described above. The gateways are mode UG65 [63] from lesight, powered at 12 V direct current (DC) using a valve-regulated lead-acid batte is based on a 64-bit 1.5 GHz ARM Cortex A53 processor, supported by 512 MB of D RAM and a flash memory of 8 GB. It supports external and internal antennas, wit output power at the output stage for LoRaWAN of 27 dBm and a sensitivity of −140 The working band is EU868 which stands for European band, with acenter frequen 868 MHz. The LTE-interfaced gateways are assembled in a waterproof IP65 enclo with the supply system. The rated typical total power of the gateway is 2.9 W. The o ating temperature range of the gateways is −40 °C to +70 °C.
The solar panel is a IP65 polycrystalline type, model NX30P from Energiasolar [64], with 344 mm length, 645 mm width and 25 mm height. The weight is 2.4 kg fo whole package in aluminum frame. The peak power is 30 W, and it reports an open ci voltage of around 21 V. The battery charge regulator is an EP5 [65] model PWM-b device. It features overcurrent and reverse polarity protection, working at 13.8 V ba charge, retaining voltage. The storage is implemented using a PCA12-12 [66] battery Prime, which powers the LoRaWAN gateway through a DC jack. In Figure 9, the gat mounting scheme is reported.

Measured Data
The system is in operation with a full uptime. However, it is possible to observe that not all the nodes are able to transmit the same quantity of data, as some are situated in locations where the LoRa signal does not always reach the gateway successfully. For this reason, some nodes will report an inferior number of points per data graph over the same time period.
The GPS unit allows tracking of the sensor nodes. This is useful in different cases: locating a node for maintenance, position acknowledgment in case of rockfall events, and to enable the fastest and more effective risk-reduction-technique and hazard plan. In case of vandalism, it is possible to locate the node, if it is active, by following the tracked GPS position. In Figures 10 and 11 some pictures showing the location of the sensor nodes in Pantelleria Island are given.
The GPS unit allows tracking of the sensor nodes. This is useful in different cases locating a node for maintenance, position acknowledgment in case of rockfall events, and to enable the fastest and more effective risk-reduction-technique and hazard plan. In case of vandalism, it is possible to locate the node, if it is active, by following the tracked GPS position. In Figures 10 and 11 some pictures showing the location of the sensor nodes in Pantelleria Island are given.  Some data plots (Figures 12-24) are reported. They are related to the period 1-25 July 2022.
Due to the effectiveness of solar harvesting, it is possible to observe (see Figure 16 the average value of battery voltage for 12 nodes of about 4.14 V, which is almost full level Only one node (node 08) reports a descending battery voltage, meaning that the light is not enough to activate the charging mechanism. The maintenance operators can monitor the status of the battery and charge the node when needed. The acceleration values formula (Figures 12-14) have been used to obtain inclination values in degrees along the axes The GPS unit allows tracking of the sensor nodes. This is useful in different cases locating a node for maintenance, position acknowledgment in case of rockfall events, and to enable the fastest and more effective risk-reduction-technique and hazard plan. In case of vandalism, it is possible to locate the node, if it is active, by following the tracked GPS position. In Figures 10 and 11 some pictures showing the location of the sensor nodes in Pantelleria Island are given.  Some data plots (Figures 12-24) are reported. They are related to the period 1-25 July 2022.
Due to the effectiveness of solar harvesting, it is possible to observe (see Figure 16 the average value of battery voltage for 12 nodes of about 4.14 V, which is almost full level Only one node (node 08) reports a descending battery voltage, meaning that the light is not enough to activate the charging mechanism. The maintenance operators can monitor the status of the battery and charge the node when needed. The acceleration values formula (Figures 12-14) have been used to obtain inclination values in degrees along the axes The measured temperature is the internal temperature in the sensor nodes box ( ure 15). In Figures 17 and 18 the received barometric pressure and altitude data are ported. Relative humidity received from the 12 nodes is observable in Figure 19. The resistance value (Figure 20) is currently indicated as standalone information but can previously stated, be used to calculate AQI using Bosch's Software.
Inclination values along the three axes are plotted in the graphs in Figures 21-24 the considered WSN nodes use the adaptive data rate (ADR) [67,68] feature of LoRaW a mechanism for optimizing data rates, airtime, and energy consumption. The netw server indicates to the end device to modify its transmission parameters in orde achieve minor airtime, hence power consumption, on the basis of the received signa tensity and signal to noise ratio (SNR). It is possible to observe ( Figure 24) that the no 10, 11, 12 do not benefit from an ideal LoRa connection with the gateway, as some pac were missed during the considered time span. However, due to the portability of the g way assembly, it is possible to find the optimal point for reception. The system is curre operating under tests to achieve better performances.                             Inclination along x, y, and z axes for nodes 10-12 from 1 July 2022 to 25 July 2022.
The described system allows for flexibility of the WSN thanks to its fully port nature with respect to the aforementioned state-of-the-art implementations, such as where a trailer with a computer is necessary for cellular network access. The key fact the use of free access MAC layer through The Things Network Stack service, which bles a faster and cheaper implementation of the system. Moreover, being the aforem tioned platform for LoRaWAN users rapidly spreading across all the planet, there strong emphasis on development which leads to up-to-date features, both in term modularity and security. Security is, in fact, granted in LoRaWAN by standardized c tographic AES algorithms [69]. In custom implementations, such as the one previo    Inclination along x, y, and z axes for nodes 10-12 from 1 July 2022 to 25 July 2022.
The described system allows for flexibility of the WSN thanks to its fully port nature with respect to the aforementioned state-of-the-art implementations, such as where a trailer with a computer is necessary for cellular network access. The key fact the use of free access MAC layer through The Things Network Stack service, which bles a faster and cheaper implementation of the system. Moreover, being the aforem tioned platform for LoRaWAN users rapidly spreading across all the planet, there strong emphasis on development which leads to up-to-date features, both in term modularity and security. Security is, in fact, granted in LoRaWAN by standardized c tographic AES algorithms [69]. In custom implementations, such as the one previo    Inclination along x, y, and z axes for nodes 10-12 from 1 July 2022 to 25 July 2022.
The described system allows for flexibility of the WSN thanks to its fully port nature with respect to the aforementioned state-of-the-art implementations, such as where a trailer with a computer is necessary for cellular network access. The key fact the use of free access MAC layer through The Things Network Stack service, which bles a faster and cheaper implementation of the system. Moreover, being the aforem tioned platform for LoRaWAN users rapidly spreading across all the planet, there strong emphasis on development which leads to up-to-date features, both in term modularity and security. Security is, in fact, granted in LoRaWAN by standardized c tographic AES algorithms [69]. In custom implementations, such as the one previo Due to the effectiveness of solar harvesting, it is possible to observe (see Figure 16) the average value of battery voltage for 12 nodes of about 4.14 V, which is almost full level. Only one node (node 08) reports a descending battery voltage, meaning that the light is not enough to activate the charging mechanism. The maintenance operators can monitor the status of the battery and charge the node when needed. The acceleration values formula (Figures 12-14) have been used to obtain inclination values in degrees along the axes using the following. In this case, INC x means x axis inclination, a x , a y , a z accelerations along x, y, and z axes expressed in m s 2 . Inclinations along the other two axes are calculated by substituting the acceleration value at the numerator of cos −1 with the acceleration on the desired axes.
The measured temperature is the internal temperature in the sensor nodes box ( Figure 15). In Figures 17 and 18 the received barometric pressure and altitude data are reported. Relative humidity received from the 12 nodes is observable in Figure 19. The gas resistance value ( Figure 20) is currently indicated as standalone information but can, as previously stated, be used to calculate AQI using Bosch's Software.
Inclination values along the three axes are plotted in the graphs in Figures 21-24. All the considered WSN nodes use the adaptive data rate (ADR) [67,68] feature of LoRaWAN, a mechanism for optimizing data rates, airtime, and energy consumption. The network server indicates to the end device to modify its transmission parameters in order to achieve minor airtime, hence power consumption, on the basis of the received signal intensity and signal to noise ratio (SNR). It is possible to observe ( Figure 24) that the nodes 10, 11, 12 do not benefit from an ideal LoRa connection with the gateway, as some packets were missed during the considered time span. However, due to the portability of the gateway assembly, it is possible to find the optimal point for reception. The system is currently operating under tests to achieve better performances.
The described system allows for flexibility of the WSN thanks to its fully portable nature with respect to the aforementioned state-of-the-art implementations, such as [18] where a trailer with a computer is necessary for cellular network access. The key factor is the use of free access MAC layer through The Things Network Stack service, which enables a faster and cheaper implementation of the system. Moreover, being the aforementioned platform for LoRaWAN users rapidly spreading across all the planet, there is a strong emphasis on development which leads to up-to-date features, both in terms of modularity and security. Security is, in fact, granted in LoRaWAN by standardized cryptographic AES algorithms [69]. In custom implementations, such as the one previously described in [23], the structures for data exchange between platforms and post processing can implemented in various manners. In a low-cost WSN this should be addressed in the most economically efficient manner as possible. For this reason, the present study implements web services which are freely accessible, demonstrating how it is feasible to implement fully working systems with low expenses. Moreover, the modularity of the system benefits from using standalone building blocks: the sensor nodes can be equipped with different and various hardware, but the LoRa blocks from the transmission stage forward can remain the same.

Conclusions
In this paper, a standalone rockfall and landslide monitoring system, with enhanced environmental monitoring capabilities, was presented, covering the hardware, firmware, and software design of a remote monitoring system, implementing it on low cost hardware and giving a complete view of a real scenario installation. For each element, the following parameters have been monitored: axial accelerations, temperature, barometric pressure, altitude, relative humidity, gas resistance for air AQI, and battery level. The system is composed of sensor nodes which communicate with gateways in star topology through the LoRa wireless modulation technique, forming a wireless sensor network structure. The WSN was installed in a real scenario, in Pantelleria Island, on rockfall barriers in two risk-subjected locations. The monitoring system is operating in support of safety for local viability and hazard reduction. The hardware structure of nodes was presented, along with the gateway system which allows portable LoRaWAN access using cellular connectivity. Power consumption measurements of the nodes are reported, with considerations on the energetic performances, reporting an energy sufficiency estimated at 2.8 years in absence of solar harvesting interventions. Experimental data extracted from the web user interface are provided for the period of July 2022, showing the measured parameters for different sensor nodes. The inclinations along three special axes, calculated using accelerometric data, do not show significant rockfall events in the reported period. As the sensing elements are placed in two groups at distances that do not allow the environmental conditions to vary in significantly observable manner, the recorded environmental data over the sample period is similar for all the nodes. It is possible to observe different behavior in radio communication due to the unfavorable position of nodes 10-12, with respect to the LoRaWAN gateway. Future developments of this work will be in the optimization of packet transmission in terms of packet loss (as it is possible to observe that nodes that do not successfully reach a gateway introduce information losses), possibly implementing different resource allocation algorithms, such as retransmission-assisted resource management [70]. Other future works will be the introduction of different sensors in the nodes to develop a yet more multifunction-oriented low-cost device.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy policies.