## 2 Materials and Methods
### Sensors and Wireless Sensor Network (WSN)  
Table 1 shows the environmental variables measured in the CSGs and the specifications of the sensors used for the measurements. Air temperature and humidity were measured using a temperature and humidity sensor (AM2315, Aosong Electronics Co., Ltd., Guangzhou, China). The sensor consists of a capacitive sensor wet component and a high-precision temperature measuring unit with a microprocessor. The carbon dioxide (CO\({}_{2}\)) concentration was detected with a CO\({}_{2}\) sensor (SH-300-ND, SOHA TECH Co., Ltd., Seoul, Republic of Korea) using a cutting-edge NDIR (non-dispersive infrared) method. A light intensity sensor (BH1750 FVI, Rohm Co., Ltd., Kyoto, Japan) employing a photoresistor technique was used to obtain the light intensity inside and outside of the greenhouses. Solar radiation was estimated using a silicon pyranometer sensor (Watchdog 3670 WS2, Spectrum Technologies, Inc., Aurora, IL, USA), and an anemometer (Davis 7911, Davis Instruments Corp. Inc., Hayward, CA, USA) was used to measure the wind speed and direction outside of the CSGs.  
Figure 1: Experimental CSGs at Shenyang Agriculture University, Liaoning, China: (**a**) cross-sectional view of the CSG, (**b**) exterior view of the CSG without crops, (**c**) interior view of the CSG without crops, (**d**) external view of the GSG with crops, and (**e**) interior view of the CSG with crops.  
A wireless sensor network (WSN) was used to collect data from the sensors using an Arduino UNO 328 (Arduino, arduino.cc) microcontroller with a 2.4 GHz radio/wireless data transmission module (nRF24L01, Shenzhen Yuzens Electronics Co., Ltd., Shenzhen, China) with a wireless data transmission range of approximately 1000 m [38]. Arduino is an open-source software and hardware platform, and the core of the Arduino UNO processor is the ATmega328. It has 14 digital input/output roads (6 of the roads can be used as a PWM output), 6 analog input roads, 32 kB of flash memory, and 1 kB of EEPROM [39], NRF24L01 is a new high-speed (20 bit/s) data transceiver for the worldwide 2.4-2.5 GHz ISM frequency band. NRF24L01 has several low-powered operation modes, such as power-down mode and standby mode. The wireless system consists of nodes, gateways, and servers. The sensor nodes were composed of an Arduino UNO 328 microcontroller, respective sensors, power sources, and nRF24L01 2.4 GHz radio/wireless transceiver modules. For the wireless sensor network gateway, nRF24L01 2.4 GHz radio/wireless transceiver modules were also attached to the same node. The gateway functions to collect data from each node and sends them to the server, which employs the Parallax Data Acquisition Tool (PLX-DAQ) to store and display the gathered information to the PC. Figure 2 shows the wiring connection between Arduino UNO, nRF24L01, temperature, and humidity sensors in the wireless network system.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Variable** & **Temperature** & **Humidity** & **CO2** & **Light** & **Solar** & **Wind Speed** & **Wind Direction** \\ \hline Model & AM2315 & AM2315 & SH-300-ND & BH1750 FVI & Watchdog & Davis 7911 & Davis 7911 \\ Range & \(-\)20–80 \({}^{\circ}\)C & 0–100\% & 0–3000 ppm & 0–65,535 lx & 0–1500 & 0.5–89 & 0\({}^{\circ}\)–360\({}^{\circ}\) \\ Resolution & 0.1 \({}^{\circ}\)C & 0.1\% & 1 ppm & 0.1 lx & 0.1 W m\({}^{-2}\) & 0.1 m s\({}^{-1}\) & 1\({}^{\circ}\) \\ Accuracy & \(\pm\)0.1 \({}^{\circ}\)C & 2\% & 2\% & \(\pm\)5\% & \(\pm\)1\% & \(\pm\)5\% & 7\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: Environmental variables measured, and the specification of sensors used.  
Figure 2: The wiring connection of **(a)** nRF24L01, Arduino UNO, and environmental sensors ((i) temperature and humidity, (ii) CO2, (iii) light sensor, (iv) solar radiation, and (v) wind speed and direction) as a transmitter node, and **(b)** nRF24L01 and Arduino UNO as a receiver node.