Abstract
Abstract. Information about the 3D structure of understory vegetation is of high relevance in forestry research and management (e.g., for complete biomass estimations). However, it has been hardly investigated systematically with state-of-the-art methods such as static terrestrial laser scanning (TLS) or laser scanning from unmanned aerial vehicle platforms (ULS). A prominent challenge for scanning forests is posed by occlusion, calling for proper TLS scan position or ULS flight line configurations in order to achieve an accurate representation of understory vegetation. The aim of our study is to examine the effect of TLS or ULS scanning strategies on (1) the height of individual understory trees and (2) understory canopy height raster models. We simulate full-waveform TLS and ULS point clouds of a virtual forest plot captured from various combinations of max. 12 TLS scan positions or 3 ULS flight lines. The accuracy of the respective datasets is evaluated with reference values given by the virtually scanned 3D triangle mesh tree models. TLS tree height underestimations range up to 1.84 m (15.30 % of tree height) for single TLS scan positions, but combining three scan positions reduces the underestimation to maximum 0.31 m (2.41 %). Combining ULS flight lines also results in improved tree height representation, with a maximum underestimation of 0.24 m (2.15 %). The presented simulation approach offers a complementary source of information for efficient planning of field campaigns aiming at understory vegetation modelling.
Highlights
Information about the state and development of forests is of crucial importance due to the eminent role which forests play, for example, as carbon sinks, habitats, provider of ecosystem services, and basis for economic exploitation (Kükenbrink et al 2016, Chen and Wang 2016)
In case of the 12 point clouds simulated for the single terrestrial laser scanning (TLS) scan positions, the 180 difference values (15 understory trees x 12 point clouds) reach a maximum tree height underestimation of 1.84 m, corresponding to 15.30% of the respective tree
We examine different TLS scan position and unmanned aerial vehicleborne laser scanning (ULS) flight line configurations regarding their effect on understory vegetation height parameters
Summary
Information about the state and development of forests is of crucial importance due to the eminent role which forests play, for example, as carbon sinks, habitats, provider of ecosystem services, and basis for economic exploitation (Kükenbrink et al 2016, Chen and Wang 2016). Methods that capture and analyse the complete volume embraced by forest stands allow the investigation of the understory in addition to the canopy surface of dominant trees (Liang et al 2016, Marselis et al 2016, Seidel et al 2016). A method broadly used for vegetation studies is laser scanning, which is especially well suited due to its capacity to penetrate vegetation through small gaps in the canopy, allowing for the acquisition of measurements which cover the whole volume of a forest stand. Research on understory vegetation benefits from the mentioned approaches because of a higher measurement density within the whole volume covered by a forest stand.
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