Abstract
Terrestrial laser scanning (TLS) and unmanned aerial vehicles (UAVs) equipped with digital cameras have attracted much attention from the forestry community as potential tools for forest inventories and forest monitoring. This research fills a knowledge gap about the viability and dissimilarities of using these technologies for measuring the top of canopy structure in tropical forests. In an empirical study with data acquired in a Guyanese tropical forest, we assessed the differences between top of canopy models (TCMs) derived from TLS measurements and from UAV imagery, processed using structure from motion. Firstly, canopy gaps lead to differences in TCMs derived from TLS and UAVs. UAV TCMs overestimate canopy height in gap areas and often fail to represent smaller gaps altogether. Secondly, it was demonstrated that forest change caused by logging can be detected by both TLS and UAV TCMs, although it is better depicted by the TLS. Thirdly, this research shows that both TLS and UAV TCMs are sensitive to the small variations in sensor positions during data collection. TCMs rendered from UAV data acquired over the same area at different moments are more similar (RMSE 0.11–0.63 m for tree height, and 0.14–3.05 m for gap areas) than those rendered from TLS data (RMSE 0.21–1.21 m for trees, and 1.02–2.48 m for gaps). This study provides support for a more informed decision for choosing between TLS and UAV TCMs to assess top of canopy in a tropical forest by advancing our understanding on: (i) how these technologies capture the top of the canopy, (ii) why their ability to reproduce the same model varies over repeated surveying sessions and (iii) general considerations such as the area coverage, costs, fieldwork time and processing requirements needed.
Highlights
Forest ecosystems are an important global resource playing key roles in both the environment and the economy
top of canopy models (TCMs) rendered from unmanned aerial vehicles (UAVs) data acquired over the same area at different moments are more similar (RMSE 0.11–0.63 m for tree height, and 0.14–3.05 m for gap areas) than those rendered from terrestrial laser scanning (TLS) data (RMSE 0.21–1.21 m for trees, and 1.02–2.48 m for gaps)
This study provides support for a more informed decision for choosing between TLS and UAV TCMs to assess top of canopy in a tropical forest by advancing our understanding on: (i) how these technologies capture the top of the canopy, (ii) why their ability to reproduce the same model varies over repeated surveying sessions and (iii) general considerations such as the area coverage, costs, fieldwork time and processing requirements needed
Summary
Forest ecosystems are an important global resource playing key roles in both the environment and the economy. Remote sensing techniques are increasingly valued by ecologists for the unique perspective they offer to describe ecosystem states and dynamics [2] They have proven to be successful when it comes to understanding forest structure, from plot-scale measurements using terrestrial laser scanning (TLS) [3,4,5,6,7,8,9], to mesoscale (1–100 km2) using aerial laser scanning [10,11,12,13,14] and aerial imagery [15,16,17], and up to global-scale perspective from satellite imagery [18,19], radar [20] and light detection and ranging (LiDAR) [21,22].
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