2.2.1. UAV Image Data

UAV data for this study were captured using a DJI Phantom 4 multispectral. The camera system offers five single-spectral cameras (blue (450 ± 16 nm), green (560 ± 16 nm), red (650 ± 16 nm), red edge (730 ± 16 nm), and infrared (840 ± 26 nm)) as well as an RGB camera. Each sensor has a resolution of 2.08 Megapixels and a focal length of 5.74 mm. Due to the flight altitude of 35 m a resolution of less then two centimeters was achieved. Images were taken on four dates during the first growth *G*<sup>1</sup> (Table 1, *G*1*T*0-*G*1*T*3), and four dates during the second growth *G*<sup>2</sup> (Table 1, *G*2*T*0-*G*2*T*3). Flights took place during noon (between 11 am and 3 pm) to minimize the influence of shadows. Each flight took about 30 to 35 min. The weather conditions on the observation days were inconsistent (see Table 1). Eight to ten field targets were placed before the flights and used as ground control points (GCPs). The center of each target was located using a differential GPS (bi-frequent GNSS receiver). On each observation day, around 350 images per channel were made with a front and side overlap of 70%. The images were stitched to a multispectral orthomosaic using

Agisoft Metashape software (version V1.7.2), georeferenced using the GCPs, and clipped to the extent of the study site.

**Table 1.** Growth, observation dates and times, number of botanically observed plots, weather conditions, and wind speed during the flights.


2.2.2. Vegetation Surveys in the Field

A total of 30 plots were stratified randomly distributed and marked during the first growth. For this, homogeneous areas were visually identified based on dominant species and 1 m × 1 m plots were placed. The four corner points of a plot were captured using a differential GPS. The area of one square meter is less than the minimum area of 10–25 m<sup>2</sup> recommended for botanical examinations in pastures [18], but to generate a variety of training data, a smaller plot size was chosen. At date *G*1*T*3, plot 26 was damaged and some of the vegetation was removed, leaving only 29 plots to be recorded (Table 1). After the first mowing, the existing plots were marked again and extended by five more plots. On six observation days, *T*1–*T*<sup>3</sup> in each growth, vegetation relevés were recorded by visual cover estimation after the UAV flight using the scale of [39]. As many characteristic and indicative species were not fully grown at both *G*1*T*<sup>0</sup> (early in the vegetation period) and *G*2*T*<sup>0</sup> (immediately after mowing), no botanical data were recorded at these times.
