Estimating above ground biomass in a Salix plantation using high resolution UAV images

Sammanfattning: In forest biomass estimations, three dimensional (3D) canopy structure data derived from images captured by unmanned aerial vehicles (UAVs), also known as drones, has shown potential due to the flexibility and cost efficiency of the method. However, little research has been done for its applicability in bioenergy forest. In this study, a method was developed with the purpose of remotely estimating the above ground biomass of a bioenergy Salix stand in southern Sweden. The main aim was to design the method so that all the required input could be collected from a consumer grade UAV, making the application simple and at a relatively low cost. A 3D structure, or point cloud, of the Salix canopy was developed through structure from motion analysis of multiple overlapping aerial images. Images collected from both a RGB sensor and a multispectral sensor were tested when developing the point cloud. The biomass was estimated in each 3.55 meter cell of a grid by an allometric equation based on the structural characteristics of the canopy. The results were compared to the harvest yield. The obtained standing biomass showed an underestimation by 8%, of the 105 ton harvest yield, which indicates that the method performed well for the study site. However, it was concluded that more testing is needed to fully evaluate the method. This study provides a suggestion on how 3D data can be used for remotely estimating biomass in a bioenergy Salix forest which can be valuable information for land owners in management decisions to improve the economic viability