Use of an UAV for Biomass Monitoring of Hairy Vetch

Abstract. Unmanned aircraft vehicles (UAVs) are currently gaining more interest in agriculture due to their ability to monitor the biomass and yield of crops. Using UAV aerial images could help in determining characteristic spots in crop areas and observing a change in plant health over time. Hairy vetch is an annual leguminous cover crop that can be used for supplying N needs of the following crop while providing weed control. The objectives of this study were to monitor the biomass of hairy vetch grown in paddy fields prior to rice cultivation using an UAV equipped with a RGB camera and a NIR camera. Original images acquired from the RGB and NIR camera were mosaicked and georeferenced, and converted into various vegetation index images such as NDVI (Normalized Difference Vegetation Index), GNDVI (Green Normalized Difference Vegetation Index) and Excess Green (ExG). In order to determine optimal vegetation indices used to estimate the biomass of the green manure for the rice field, ground truth data including biomass and growth status were obtained at ground control points sampled with a RTK-DGPS receiver. The results showed that there were strongly linear relationships between the biomass and nitrogen content (coefficients of determinations of 0.7~0.8 when using the NDVI, GNDVI, ExG vegetation indexes.