Abstract
Unmanned aerial vehicles (UAVs) and digital photogrammetric techniques are two recent advances in remote sensing (RS) technology that are emerging as alternatives to high-cost airborne laser scanning (ALS) data sources. Despite the potential of UAVs in forestry applications, very few studies have included detailed analyses of UAV photogrammetric products at larger scales or over a range of forest types, including mixed conifer–broadleaf forests. In this study, we assessed the performance of fixed-wing UAV photogrammetric products of a mixed conifer–broadleaf forest with varying levels of canopy structural complexity. We demonstrate that fixed-wing UAVs are capable of efficiently collecting image data at local scales and that UAV imagery can be effectively utilized with digital photogrammetric techniques to provide detailed automated reconstruction of the three-dimensional (3D) canopy surface of mixed conifer–broadleaf forests. When combined with an accurate digital terrain model (DTM), UAV photogrammetric products are promising for producing reliable structural measurements of the forest canopy. However, the performance of UAV photogrammetric products is likely to be influenced by the structural complexity of the forest canopy. Furthermore, we highlight the potential of fixed-wing UAVs in operational forest management at the forest management compartment level, for acquiring high-resolution imagery at low cost. A future direction of this research would be to address the issue of how well the photogrammetric products can predict the actual structure of mixed conifer–broadleaf forests.
Highlights
Forest canopy structure has many components but often refers to the size and spatial arrangement of overstory trees as described by the vertical and horizontal distributions of overstory foliage [1,2]
The Unmanned aerial vehicles (UAVs)-structure from motion (SfM) technique provided a fair characterisation of a mixed conifer–broadleaf forest canopy with varying levels of structural complexity comparable to the results of high-cost airborne light detection and ranging (LiDAR) observation
Our results highlight that there’re differences in between airborne laser scanning and digital photogrammetry techniques, digital photogrammetric products developed using fixed-wing UAV imagery over the mixed conifer–broadleaf forests in northern Japan performed well in characterising forest canopy structure and predicting forest structural attributes that are commonly used in forestry applications
Summary
Forest canopy structure has many components but often refers to the size and spatial arrangement of overstory trees as described by the vertical and horizontal distributions of overstory foliage [1,2]. Our understanding of forest canopy structure may be constrained in some important ways (e.g., structural and spatial complexity of the canopy at the landscape level) because most existing studies of the forest canopy are based on data collected through field surveys within a small set of sample plots that are often selected subjectively [8,9]. RS has proven an effective means of studying forest canopy structure, as it often complements existing ground-based techniques by contributing reliable, detailed information on various aspects of the complex forest canopy [12,13,14]. Recent advances in RS technology, such as airborne laser scanning (ALS), digital photogrammetry, and unmanned aerial vehicle (UAV) systems, have enabled efficient data collection and fully automated reconstruction of forest canopy surfaces over large spatial areas [15,16,17,18,19,20,21,22]
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