# Unmanned Aerial Vehicle Based Wireless Sensor Network for Marine-Coastal Environment Monitoring
## 4 Experimentation and Results
### Methodology  
As the LoRa communications play a key role in the system, it was one of the first things that needed to be tested. As stated previously, the LoRa modulation has been widely studied and its achievable range proven, yet its operation at 433 MHz has not been analyzed in detail. This analysis, and a comparison with the 868 MHz band, was done in a previous study [32], where several RF configurations were tested with a beta version of the sensor node communications block. From this experimentation, several LoRa RF configurations were selected for further technical testing.  
With the control and sensor node hardware used in this article, stress and stability tests were done in a laboratory. Periodically, the sensor node would capture data from all the ambient sensors  
Figure 12: Graphical user interface screenshot.  
and GPS module, store the data in its memory and await LoRaNET messages. The control node was configured to automatically create a network, search and recruit sensor nodes, and download their data. This was accomplished with the master node connected directly to the GIU. These tests were done several times, after fixing the identified coding errors, until the firmware and software of the devices were stable for the next trials.  
To accomplish the third objective, several experimentations were deemed necessary. The first trial was done by transmitting a sequence of data packages across a shore line with both transceivers at sea level, trying to emulate LoRa transmissions in the worst-case scenario. For this trial, various LoRa RF configurations were tested, whilst maintaining the operation frequency at 433 MHz, as was required. Amongst these configurations, it was also possible to validate the spreading factor of 128 chips/symbol, bandwidth of 125 kHz, and coding rate 4/5 RF LoRa configuration, which was not verified in the first 433 MHz analysis. This last configuration test yielded an approximate transmission range of 5 km.  
Afterwards, there was a need to verify if the LoRa transceiver communications would have any type of negative impact on the wireless communications used in the UAVs autopilot module, given the similar frequencies to the 433 MHz band. In the same location of the last trial, LoRa data packages were transmitted across the shore line whilst simultaneously transmitting with the UAVs FY-605 transceiver at 434 MHz to a computer with the GCS software. Although the FY-605 is to be used in the 462.125 MHz band, it was configured to 434 MHz to also emulate a worst-case scenario. Across the whole experiment, there was no visible interference in the GCS software or LoRa transmissions.  
Even though this previous trial practically guaranteed that the LoRa master node could operate without interference, a final test was done to truly validate the communications in flight. This experiment was done using a sensor node placed on the ground, a network monitor node connected to a computer with the GUI and by mounting a master control node inside the UAV (Figure 13).  
Having placed the master node in the UAV, the aircraft was flown in manual mode in close proximity to the sensor node in a circular pattern. This test granted the last successful validation of the system, prior to the final field test.  
Figure 13: Initial flight test. To the left the sensor buoy placed on the ground and to the right the UAV with the master node mounted inside.