Crop biomass and height from UAV-based LiDAR

doi:10.3390/rs12010017

Phenotyping of crops is important to estimate biomass and the potential yield of new varieties of agricultural crops. Phenotyping of individual plants can be done in very high detail with LiDAR which is scanning the 3D structure of the complete plant. Earlier studies have used LiDAR scanners on tractors or stand-alone in the field. In the last few years, LiDAR systems have been miniaturized, resulting in lower weights and reduced dimensions, and as a result, can be operated from Unmanned Aerial Vehicles (UAV). This development opens the way towards high throughput derived, more complex products like biomass and yield, thus, improving the speed and frequency at which these plant traits can be acquired in the field in an undisturbed way. Jelle ten Harkel and his colleagues investigated the potential of UAV-LiDAR for estimation of crop height and fresh weight biomass for three different agricultural crops. For this, the RIEGL RiCOPTER with a VUX-SYS LiDAR system was flown over fields with sugar beet, wheat, and potatoes, on a number of moments during the 2018 growing season. The results of this research are published in the journal Remote Sensing.

Abstract
Phenotyping of crops is important due to increasing pressure on food production. Therefore, an accurate estimation of biomass during the growing season can be important to optimize the yield. The potential of data acquisition by UAV-LiDAR to estimate fresh biomass and crop height was investigated for three different crops (potato, sugar beet, and winter wheat) grown in Wageningen (The Netherlands) from June to August 2018. Biomass was estimated using the 3DPI algorithm, while crop height was estimated using the mean height of a variable number of highest points for each m². The 3DPI algorithm proved to estimate biomass well for sugar beet (R² = 0.68, RMSE = 17.47 g/m²) and winter wheat (R² = 0.82, RMSE = 13.94 g/m²). Also, the height estimates worked well for sugar beet (R² = 0.70, RMSE = 7.4 cm) and wheat (R² = 0.78, RMSE = 3.4 cm). However, for potato both plant height (R² = 0.50, RMSE = 12 cm) and biomass estimation (R² = 0.24, RMSE = 22.09 g/m²), it proved to be less reliable due to the complex canopy structure and the ridges on which potatoes are grown. In general, for accurate biomass and crop height estimates using those algorithms, the flight conditions (altitude, speed, location of flight lines) should be comparable to the settings for which the models are calibrated since changing conditions do influence the estimated biomass and crop height strongly.