# Vegetation Classification in Urban Areas by Combining UAV-Based NDVI and Thermal Infrared Image
## 2 Materials and Methods
### UAV Image Processing  
In order to obtain an image of the study site, a Canon S110 NIR and ThermoMAP camera were mounted on the eBee model manufactured by SenseFly in Switzerland as shown in Figure 3.  
The fixed-wing UAV, called eBee, can capture an area of about 12 km\({}^{2}\) with a flight of more than 40 min, and has the advantage of securing a resolution of 1.5 cm when the flight altitude is low [51]. The Canon S110 NIR camera is used to calculate various vegetation indices because it can obtain RGB and near-infrared (NIR) bands, and the thermoMAP camera was used to create temperature information.  
In order to establish a UAV flight plan such as flight altitude, resolution, longitudinal overlap, and lateral overlap, eMotion S/W was used as shown in Figure 4.  
Figure 3: The UAV system.  
Figure 2: The study area.  
Since the Canon S110 NIR camera (Table 1) has a high resolution, images with a resolution of 4 cm were taken by designing 80% and 70% longitudinal and lateral overlap, respectively, at a flight altitude of 115 m as shown in Figure 4a. In addition, since the thermoMAP thermal infrared camera has a relatively low resolution, images with a resolution of 15 cm were taken by designing 95% and 70% longitudinal and lateral overlap, respectively, at a flight altitude of 80 m as shown in Figure 4b.  
Table 2 shows the details of designing a flight plan by mounting Canon S110 NIR and thermoMAP thermal infrared cameras, respectively [51].  
To secure the positional accuracy of the UAV image, six ground control points were selected as in Table 3, and Transverse Mercator (TM) coordinates of the GRS80 ellipsoid were acquired through VRS survey. The captured image has Universal Transverse Mercator (UTM) coordinates of the WGS84 ellipsoid through a Global Positioning System (GPS) receiver equipped with a UAV. Therefore, in order to convert into TM coordinates of the GRS80 ellipsoid used in Korea, the survey results were matched to ground control points. Figure 5 shows the VRS surveying for ground control point (No.1).  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Category** & **Specification** \\ \hline Band & Blue, Green, Red, NIR \\ \hline \multirow{4}{*}{Band wavelength(nm)} & Blue: 450 \\  & Green: 550 \\  & Red: 625 \\  & NIR: 850 \\ \hline Resolution & 12 Mp \\ \hline Ground resolution at 100 m & 3.5 cm/pix \\ \hline Sensor size & 7.44 \(\ast\) 5.58 mm \\ \hline Pixel pitch (width \(\ast\) height) & 1.33 um \\ \hline Image format & JPEG/CR2 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Specifications of Canon S110 NIR camera.  
Figure 4: Set up of UAV flight planning using eMotion S/W.  
As for the video taken by the UAV, as shown in Figure 6, 70 red, green, blue, and near-infrared (NIR) bands pictures were taken with a Canon s110 NIR camera and 3131 thermal-infrared bands pictures used a thermoMAP camera. The image was merged using Pix4D Mapper S/W, and the 'GCP Manger' function was used to match the surveying coordinates of the ground control point to increase the positional accuracy of the UAV image. Through this process, orthomosaic images of red, green, blue, near-infrared (Nir), and thermal-infrared bands required for vegetation index analysis were constructed (Figure 7).