Sensitivity of voxel-based estimations of leaf area density with terrestrial LiDAR to vegetation structure and sampling limitations: A simulation experiment

The need for fine scale description of vegetation structure is increasing as Leaf Area Density (LAD, m2/m3) becomes a critical parameter to understand ecosystem functioning and energy and mass fluxes in heterogeneous ecosystems. Terrestrial Laser Scanning (TLS) has shown great potential for retrievi...

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Bibliographic Details
Published in:Remote sensing of environment 2021-05, Vol.257, p.112354, Article 112354
Main Authors: Soma, Maxime, Pimont, François, Dupuy, Jean-Luc
Format: Article
Language:English
Subjects:
Bias
Canopies
Confidence intervals
Density
Fluxes
Foliage
Heterogeneity
LAI
Leaf area
Leaf area density (LAD)
Leaves
Lidar
Life Sciences
Occlusion
Random sampling
Sampling
Sampling designs
Simulation
Spatial distribution
Statistical sampling
Terrestrial environments
Terrestrial LiDAR
Vegetation
Voxel
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Summary:The need for fine scale description of vegetation structure is increasing as Leaf Area Density (LAD, m2/m3) becomes a critical parameter to understand ecosystem functioning and energy and mass fluxes in heterogeneous ecosystems. Terrestrial Laser Scanning (TLS) has shown great potential for retrieving the foliage area at stand, plant or voxel scales. Several sources of measurement errors have been identified and corrected over the past years. However, measurements remain sensitive to several factors, including, 1) voxel size and vegetation structure within voxels, 2) heterogeneity in sampling from TLS instrument (occlusion and shooting pattern), the consequences of which have been seldom analyzed at the scale of forest plots. In the present paper, we aimed at disentangling biases and errors in plot-scale measurements of LAD with TLS in a simulated vegetation scene. Two negative biases were formerly attributed to (i) the unsampled voxels and to (ii) the subgrid vegetation heterogeneity (i.e. clumping effect), and then quantified, thanks to a the simulation experiment providing known LAD references at voxel scale, vegetation manipulations and unbiased point estimators. We used confidence intervals to evaluate voxel-scale measurement accuracy. We found that the unsampled voxel effect (i) led to underestimations with the “mean layer” method –commonly used to fill unsampled voxels- for small voxels (0.1–0.2 m) and/or low number of scans (
ISSN:0034-4257
1879-0704
DOI:10.1016/j.rse.2021.112354