Estimating cover fraction from tls return intensity in coniferous and broadleaved tree shoots

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openAccess

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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä

Date

2021

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Language

en

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Silva Fennica, Volume 55, issue 4

Abstract

Terrestrial laser scanning (TLS) provides a unique opportunity to study forest canopy structure and its spatial patterns such as foliage quantity and dispersal. Using TLS point clouds for estimating leaf area density with voxel-based methods is biased by the physical dimensions of laser beams, which violates the common assumption of beams being infinitely thin. Real laser beams have a footprint size larger than several millimeters. This leads to difficulties in estimating leaf area density from light detection and ranging (LiDAR) in vegetation, where the target objects can be of similar or even smaller size than the beam footprint. To compensate for this bias, we propose a method to estimate the per-pulse cover fraction, defined as the fraction of laser beams’ footprint area that is covered by vegetation targets, using the LiDAR return intensity and an experimental calibration measurement. We applied this method to a Leica P40 single-return instrument, and report our experimental results. We found that conifer foliage had a lower average per-pulse cover fraction than broadleaved foliage, indicating an increased number of partial hits in conifer foliage. We further discuss limitations of our method that stem from unknown target properties that influence the LiDAR return intensity and highlight potential ways to overcome the limitations and manage the remaining uncertainty. Our method’s output, the per-beam cover fraction, may be useful in a weight function for methods that estimate leaf area density from LiDAR point clouds.

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| openaire: EC/H2020/771049/EU//FREEDLES Funding Information: The authors received funding from the European Research Council (ERC) under the European Funding Information: The authors received funding from the European Research Council (ERC) under the European Union?s Horizon 2020 research and innovation programme (grant agreement No 771049). The article reflects only the authors? view and the Agency is not responsible for any use that may be made of the information it contains. Funding Information: Union’s Horizon 2020 research and innovation programme (grant agreement No 771049). The article reflects only the authors’ view and the Agency is not responsible for any use that may be made of the information it contains. Publisher Copyright: © 2021, Finnish Society of Forest Science. All rights reserved.

Keywords

Leaf area, Lidar intensity, Physically-based, Terrestrial laser scanning, Voxel

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Citation

Schraik, D, Hovi, A & Rautiainen, M 2021, ' Estimating cover fraction from tls return intensity in coniferous and broadleaved tree shoots ', Silva Fennica, vol. 55, no. 4, 10533 . https://doi.org/10.14214/sf.10533