# Unmanned Aerial System-Based Data Ferrying over a Sensor Node Station Network in Maize
## 2 Materials and Methods
### Experiment Design  
The transceiver radio (Campbell Scientific's RF 450 radio) was mounted on the UAS (DJI's Matrice 600 Pro Hexacopter) along with a mini laptop, a battery source (12 V), and an antenna (Campbell Scientific's 900 MHz 0 dBd \({}^{1}\)/2 Wave Omnidirectional antenna) (Figure 5a,b). The mini-laptop and the transceiver radio were powered by a 12 V battery source. The mini laptop was connected to the primary radio via a USB cable. The antenna was connected to the radio with the antenna oriented downward. The data retrieval from the datalogger to the secondary radio was scheduled using the 'Setup' function of the 'Loggernet 4.5' software (see [PERSON], [34] for details). Five node stations were installed in the field (A-E) during the 2021 growing season (Figure 4a). One node station collapsed (the galvanized steel pipe on the tripod supporting sensors and instrumentation was corroded and it snapped) in the middle of the growing season (on 7 August 2021) due to the wind shear of a rainstorm; only two UAS flights were conducted with this station. Another node station was installed as a replacement at point 'F' in the field (Figure 4b); the remaining seven flights were made after the station at location 'F' was installed. The sensor node station comprised of a secondary radio (Campbell Scientific's RF 450 radio), an antenna (Campbell Scientific's 900 MHz 1 dBd Omnidirectional antenna), a datalogger (Campbell Scientific's CR1000X datalogger), a battery source (12 V), soil water content sensors (MeterEnvironment's GS-1), and an infrared thermometer (IRT) sensor (Apogee Instruments SI-111, Logan, UT, USA). The secondary radio, the antenna, the datalogger, the battery source, and the wires for soil water content sensors and infrared radiometer were enclosed in an enclosure box (Figure 6a,b). The enclosure box was mounted at a height of 1.5 m above ground for stations B, D, and E, and 0.6 m above the ground for stations A and C during the first two experimental trials. During the third experimental trial in 2020, all the enclosure boxes were mounted at a height of 1.5 m above the ground. The location of the enclosure box places the antenna within the canopy when the maize is at full height. The secondary radio was connected to the datalogger via a null modem cable. The soil water content sensors were inserted at a depth of 0.15 m, 0.46 m, and 0.76 m, respectively. The IRT sensor was mounted at a constant height of 1 m above the maize canopy consistently throughout the growing season. All node station sensors were connected to the datalogger. The output from the sensors was recorded at a 5 s sampling frequency and averaged every 15 min. Figure 5: (**a**) The Matrice 600 Pro Hexacopter at the research farm; (**b**) a close-up view of the hexacopter along with the primary radio and the mini laptop. Soil moisture, canopy temperature, and air temperature data were transmitted from the datalogger through the secondary RF450 radio to the transceiver (primary) RF450 radio mounted on the UAS. Communication success and data transmission and receipt were assessed at different UAS heights (31 m, 61 m, and 122 m above the ground) in 2020, and at different lateral distances of the UAS from the node stations (0 m, 38 m, and 76 m) at a height of 31 m above the ground in 2021. Communication success was quantified in terms of CSR (in %). The CSR for each treatment and each trial day was calculated as:  
\[\text{CSR (in \%)}=\frac{\text{N}_{\text{established}}}{\text{N}_{\text{ attempted}}}\times 100 \tag{1}\]  
where CSR is communication success rate, \(\text{N}_{\text{established}}\) is the number of replications where the communication was established, and \(\text{N}_{\text{attempted}}\) is the number of replications where communication was attempted. Wireless communication and data retrieval on the UAS data ferry was scheduled via the UAS-mounted mini laptop.