Estimation of plant height using UAS with RTK GNSS technology

Plant height is an important trait in crop breeding as it has high correlations with grain yield, biomass, and stress tolerance. Most of the studies so far for field-based high-throughput plant height phenotyping with UAS rely on ground control points (GCPs) for geometric calibrations due to the limited positioning accuracy of the GPS onboard. Setting up these GCPs is labor-intensive and is not feasible for a large field. The advent of commercial UAS equipped with Real-Time Kinematic (RTK) Global navigation satellite system (GNSS) technology are expected to achieve a centimeter-level positioning accuracy and have the potential of expediting and improving plant height phenotyping process. Hence, the objective of our study was to investigate the potential and dependency on GCPS of RTK GNSS enabled UAS technology and compare its performance to regular differential GNSS on plant height estimation. In the summer of 2021, images were corrected with two UAS - one with RTK GNSS; and the other with regular differential GNSS - for three different methods over cornfields: Method 1 used both the differential GNSS and the GCPs; Method 2 used both the RTK GNSS with the real-time corrections via cellular network and the GCPs; Method 3 used only the RTK GNSS with the real time corrections via cellular network but without GCPs. In this study, method 2 and 3 resulted with close accuracies, with a R² of 0.775 for method 2 and a R²of 0.760 for method 3 in maize plant height estimation. Method 1 had the lowest correlation (R² = 0.250) in this study mostly due to the less data and data quality issues. Results from the study showed that the RTK GNSS enabled UAS has the potential and less dependency on GCPs in deriving accurate horizontal positioning and estimating plant height. Aerial surveys and plant phenotyping with RTK GNSS enabled UAS are more convenient and easily deployed in plant phenotyping and precision agriculture.