*3.4. Influence of Flight Characteristics on Biomass*

Biomass maps based on the 3DPI scores show varying patterns of biomass, dependent on the flight characteristics (Figure 10). The absolute differences, compared to flight Day2-MA-MS (40 m, 6 m/s), are more clearly visible in Figure 10. Flying higher and faster (DAY3-HA-HS), results in an underestimation of the amount of biomass. For flight DAY3-HA-HS, the average biomass estimation was 1622.1 g/m2, where for Day2-MA-MS, the average biomass estimation was 2479.7 g/m<sup>2</sup> (Table 5). For the other flight characteristics, the overall estimate of biomass does not deviate too much from the standard flight settings, but there are locations where the estimated biomass for the adapted flights is lower compared to the standard flight. Further investigations learned that those areas are located exactly between two flight lines. It is important to indicate that the exact position of the flight lines was not consistent for the different flights. For each of the flights with the standard settings, the same pre-programmed flight paths were used, but for the flights with adapted altitude and speed, new flight plans were made, resulting in different flight patterns. This results in a different point density and point distribution along the dataset, which appears to influence the estimated biomass more than the altitude and speed.

**Figure 10.** Maps indicating for flight DAY2-LA-MS, DAY2-LA-LS, DAY3-HA-HS, and DAY3-LA-LS the estimated biomass in grams for winter wheat. Darker greens mean a larger biomass prediction.

**Table 5.** Overview of mean and standard deviation for the flights discussed in Figures 8–10. The data for plant heights are from sugar beet, and the data for the biomass data are from the winter wheat maps. For Day1-MA-MS, Day2-MA-MS and Day4-MA-MS, there is no data (nd) in the difference cell because these were not compared to Day2-MA-MS.


The biomass prediction for flight Day3-HA-HS shows an under prediction compared to the other flights (Table 5), where for plant height the difference in the mean between the flights are smaller. The sugar beet plant height estimation shows almost no variation between the flight characteristics describing the field data from 29 June 2018. The biomass estimations for winter wheat does appear to be sensitive to a difference in flight characteristics. There are large differences in the mean prediction

between the different flight specifications, where for faster and higher flights (Figure 11 and Table 5: DAY3-HA-HS), an under prediction of biomass occurs compared to flight Day2-MA-MS.

**Figure 11.** Maps indicating pixel differences between the biomass prediction for winter wheat of Flight Day2-MA-MS and, respectively, DAY2-LA-MS, DAY2-LA-LS, DAY3-HA-HS, and DAY3-LA-LS. Positive values (blue) indicate a higher prediction for, respectively, DAY2-LA-MS, DAY2-LA-LS, DAY3-HA-HS, and DAY3-LA-LS compared to Day2-MA-MS.
