## 2 Materials and Methods
### Unmanned Aerial Vehicle (UAV) Data Acquisition  
The study employs the DJI Phantom 4 Multispectral (P4M) quadcopter, which is a drone equipped with multispectral imaging capabilities [33], for capturing aerial images. The P4M quadcopter is equipped with six sensors, including an RGB sensor with 2.08 megapixels, a blue sensor (450 nm \(\pm\) 16 nm), a green sensor (560 nm \(\pm\) 16 nm), a red sensor (650 nm \(\pm\) 16 nm), a red edge sensor (730 nm \(\pm\) 16 nm), and a near-infrared \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Month** & **Rainfall (mm)** & **TempAvg (\({}^{\circ}\)C)** & **TempMax (\({}^{\circ}\)C)** & **TemMin (\({}^{\circ}\)C)** & **Humidity (\%)** & **Wind Speed (km/h)** \\ \hline January & 0.45 & 24.59 & 36.37 & 14.23 & 66.50 & 4.10 \\ February & 0.00 & 27.53 & 38.25 & 18.67 & 69.98 & 3.59 \\ March & 0.13 & 29.47 & 41.57 & 24.17 & 68.32 & 3.98 \\ April & 0.52 & 31.02 & 42.14 & 25.14 & 68.15 & 3.78 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Climate data for maize growth in the period of study of 11 January to 5 May 2013. Figure 1: Area of study located in (**a**) Manorom District, Chai Nat, Thailand, with Latitude: 15.270978, Longitude: 100.174656. (**b**) A total of 270 blocks of ROIs in Plots 1, 2, and 3 were selected for analysis. sensor (840 nm \(\pm\) 26 nm). These sensors enable the acquisition of comprehensive spectral information. The flight missions were conducted using the _DJI GS Pro_ software version 2.0.17, with specific settings applied. The settings included a speed of 3.2 milliseconds, a shutter interval of 2 seconds, a front overlap ratio of 75%, a side overlap ratio of 75%, and a course angle of 119 degrees. The UAV was flown at altitudes of 30 m and 100 m to capture data from different perspectives. In order to mitigate the influence of varying sunlight angles, the UAV flights were scheduled between 10:00 a.m. and 12:00 p.m. It is noteworthy that the maize growth stages are commonly delineated using a standardized system developed by the Food and Agriculture Organization (FAO). In the context of our research, it is of paramount importance to investigate and ascertain the potential correlations between specific growth stages and the width of maize seeds, employing an innovative and novel approach. To achieve this objective, we meticulously conducted weekly monitoring of maize growth utilizing UAVs. A total of 17 UAV flights were conducted over a comprehensive 113-day period, encompassing the entire growth cycle of the maize plants. The detailed data obtained from these flights are meticulously presented in Table 2, providing valuable insights for further analysis and interpretation. During the Vegetative Stage (VE) of maize growth, which signifies the emergence of the first leaves, our UAV observation campaign was initiated on 11 January 2023. RGB and multispectral images were acquired during this phase, utilizing UAV flights conducted at altitudes of 30 m and 100 m. The purpose of these flights was to capture comprehensive data encompassing both standard RGB imagery and multispectral information regarding the early growth patterns of maize plants. Furthermore, on day 8 of maize growth, the emergence of leaves begins. By day 56, the plant typically reaches the stage where ten leaves have appeared. In order to maintain optimal conditions for maize growth, it is crucial to address both excessive moisture and prolonged drought. These conditions have the potential to reduce the yield by up to 25% between the sixth leaf stage (V6), characterized by the development of six leaves with visible collars, and the tenth leaf stage (V10), characterized by the development of ten leaves with visible collars. To ensure the appropriate growth of maize, we consistently monitored its progress on a weekly basis across all growth stages.