The Impact of Canopy Reflectance on the 3D Structure of Individual Trees in a Mediterranean Forest

Abstract

The characterization of 3D vegetation structures is an important topic, which has been addressed by recent research in remote sensing. The forest inventory requires the proper extraction of accurate structural and functional features of individual trees. This paper presents a novel methodology to study the impact of the canopy reflectance on the 3D tree structure. A heterogeneous natural environment in a Mediterranean forest, in which various tree species (pine, oak and eucalyptus) coexist, was covered using a high-resolution digital camera and a multispectral sensor. These devices were mounted on an Unmanned Aerial Vehicle (UAV) in order to observe the tree architecture and the spectral reflectance at the same time. The Structure from Motion (SfM) method was applied to model the 3D structures using RGB images from the high-resolution camera. The geometric accuracy of the resulting point cloud was validated by georeferencing the study area through multiple ground control points (GCPs). Then, the point cloud was enriched with the reflected light in four narrow-bands (green, near-infrared, red and red-edge). Furthermore, the Normalized Difference Vegetation Index (NDVI) was calculated in order to measure the tree vigor. A comprehensive analysis based on structural and spectral features of individual trees was proposed. A spatial segmentation was developed to detect single-trees in a forest and for each one to identify the crown and trunk. Consequently, structural parameters were extracted, such as the tree height, the diameter at breast height (DBH) and the crown volume. The validation of these measurements was performed by field data, which were taken using a Total Station (TS). In addition, these characteristics were correlated with the mean reflectance in the tree canopy. Regarding the observed tree species, a statistical analysis was carried out to study the impact of reflectance on the 3D tree structure. By applying our method, a more detailed knowledge of forest dynamics can be gained and the impact of available solar irradiance on single-trees can be analyzed.

Automatic Grapevine Trunk Detection on UAV-Based Point Cloud

“…There are several methods for the automatic detection and parameters extraction on 3D models using crop height models [37], combining terrestrial laser scanner and UAV photogrammetric point clouds [38], fusing RGB and multispectral point clouds to extract individual tree parameters [39], computing 3D vegetation indices in olive groves [40], and obtaining forest structural attributes [41]. However, given the complexity and the unique characteristics of vineyard plots, such methods are not suitable to be applied.…”

Phenotyping Architecture Traits of Tree Species Using Remote Sensing Techniques

“…The estimation results showed that the relative RMSE of height ranged from 6.55% to 19.24%, and the errors depended on the architecture type and tree age. Jurado et al (2020b) assessed the impact of canopy reflectance based on the 3D tree structure of an individual treelevel forest inventory. Structural and spectral traits were extracted from images acquired using UAV-mounted RGB and multispectral cameras oriented at inclinations of 60° (for better 3D model reconstruction) and 90° (for accurate canopy reflectance measurement) relative to the ground.…”

“…Tree height is a vital agronomic trait for assessing crop status and a vital selection parameter in breeding programs, especially in field conditions (Wiersma et al, 1986;Boukerrouand Rasmusson, 1990;Moles et al, 2009). Tree height estimation is also used as an indicator to estimate biomass (Persson and Fransson, 2017;Fernández-Sarría et al, 2019;Gennaro et al, 2020), yield (Sarron et al, 2018;López-Granados et al, 2019;Stateras and Kalivas, 2020), and health (Chang et al, 2020;Hobart et al, 2020;Jurado et al, 2020aJurado et al, , 2020b. In addition, canopy height from reconstructed 3D shape models is used to evaluate crop water status for irrigation planning.…”

The UAS-Based 3D Image Characterization of Mozarabic Church Ruins in Bobastro (Malaga), Spain

“…The resulting 3D structures are modeled as a point cloud instead of a 3D mesh due to the fact that many complex geometric objects cannot be correctly triangulated. The SfM has been used for multiple purposes such as the vegetation reconstruction [19], cultural heritage [20], and archaeology [21]. Focusing on this last one, the 3D modeling of archaeological artifacts is usually carried out to study different characteristics using a virtual copy instead of the original.…”