Measuring Leaf Equivalent Water Thickness of Short-Rotation Coppice Willow Canopy Using Terrestrial Laser Scanning

Accurate measurements of leaf Equivalent Water Thickness (EWT) can help in early detection of vegetation stress. Terrestrial Laser Scanning (TLS) intensity data have the potential to provide 3D estimates of EWT, overcoming the limitations of the 2D estimates provided by remote sensing optical data. Such limitations include the sensors being solar illumination dependent and unable to provide information about the vertical variation in EWT. In this study, intensity data from the Leica P20 and P40 commercial TLS instruments were combined in a Normalized Difference Index (NDI). NDI was used to measure EWT in six short-rotation coppice willow (Salix spp.) plots from different varieties with an average error of 7.3% (R2 = 0.8, RMSE = 0.0011 g cm-2). The effects of wind and senescence of leaves on the accuracy of the EWT estimation were also investigated.