*2.2. Data Acquisition*

UAV-LiDAR data and field measurements of crop height and biomass were collected simultaneously on four dates (Table 2). For the 1st, 2nd, and 4th flight date, field data were collected on the same day, directly starting after the flight and finished within 3 to 4 hours. The 3rd flight day was not planned initially, so no field measurements were done on that day, but this flight was conducted only 2 days after the 2nd flight. Therefore, the field data collected at the day of the 2nd flight were used for both those flights.


**Table 2.** Flying dates and corresponding growth stages for the crops in selected fields.

#### 2.2.1. Field Data Collection

Plant height was measured using a ruler at 14–21 locations in each field. Locations were chosen in such a way that differences within the field were well represented. On each location, an average height was calculated based on three height measurements of randomly selected plants taken within 15 cm of each other. Biomass was determined through destructive sampling at different locations within the field, differing from the plant height sampling locations [14]. For potato and sugar beet, five biomass samples per field were taken and for winter wheat three. Biomass was harvested after the flights. Biomass samples were taken for the first, second, and fourth flight day only, which resulted in 15 samples for both potato and sugar beet and 9 samples for winter wheat. For potato, biomass was harvested for one meter along the potato ridge and converted to biomass per 1 m2. The same procedure was used for harvesting the sugar beet, where one meter in the planting direction was harvested and converted to biomass per 1 m2. For wheat, an area of 1 m2 area was harvested. Biomass was measured as fresh biomass weight directly after harvesting. Table 3 shows the mean and standard deviation of every field campaign. The location of every crop trait measurement was measured with a Topcon HIPER V RTK-GNSS system (TOPCON, Japan), which has a sub centimeter accuracy.

**Table 3.** Mean and standard deviation of field measurements separated per crop and sampling date.

