A UAV-mounted dual-wavelength LiDAR for leaf water content retrieval

Water scarcity will be an issue in many geographical regions due to an accelerating pace of global and climate change. The increase in intensity and frequency of climate extremes will bring new challenges for several sectors, including forestry, urban greenery, and agriculture. Despite the importance of monitoring the drought effects on vegetation, an effective method is still missing. <br/> The leaf water content [<i>g/cm</i>²] is an important parameter to inform about the hydration status of the plants and varies with soil water availability and evaporation losses. Moreover, the reduction of leaf water content comes with the increase in risk and intensity of wildfires. However, there is no robust and effective method to monitor the leaf water content over large areas. <br/> Traditional ways to determine the leaf water content require destructive sampling, i.e., which only gives information about individual leaves and is not necessarily transferable to large areas. For these reasons we propose an active remote sensing method by means of Light Detection and Ranging (LiDAR). Specially, a LiDAR system that is operated from an unoccupied aerial vehicle (UAV). <br/> The combination of both components, the LiDAR and the UAV, enables the possibility to characterize the 3D structure of large areas while simultaneously capturing the spectral properties of plant material. In fact, it has been shown that the LiDAR response changes according to changes in leaf water content. Here, we propose to retrieve two wavelengths simultaneously, also known as dual-wavelength LiDAR. The advantage of the dual-wavelength LiDAR system is the measurement of the water absorption while also detecting the canopy scattering components. Here, we discuss the principle, the planned approach and preliminary results.