CAN UAV LIDAR DERIVE VERTICAL STRUCTURE OF HERBACEOUS VEGETATION ON RIVERDIKE?

Abstract. Herbaceous vegetation on riverdike is important to prevent soil erosion, which may lead to collapse of riverdikes and consequently severe flooding. To keep suitable vegetation condition and secure visibility of riverdike for inspection, managers need to know where thick and tall herbaceous vegetation grows on riverdikes in a cost effective manner. This paper aims to derive vertical structure of herbaceous vegetation on riverdike using UAV LiDAR. UAV LiDAR based indices, V-bottom, V-middle and V-top; presence of vegetation in bottom vegetation (0–50 cm), middle vegetation (50–100 cm) and top vegetation (>100 cm) respectively, were calculated and compared to field survey data for validation. The results showed that UAV LiDAR based assessment strongly correlated with field based assessment in middle and top vegetation with R² = 0.67 and 0.85, respectively. However, it displayed only moderate correlation in bottom vegetation (R² = 0.36). It was found that bottom vegetation might be underestimated when forb species or falling grass species is abundant in middle vegetation. However, underestimated place can be easily checked using proposed UAV LiDAR based V-bottom and V-middle values. The vertical structure information derived by proposed method would be valuable assets for vegetation management on riverdike.