Comparison of forest canopy gap fraction measurements from drone-based video frames, below-canopy hemispherical photography, and airborne laser scanning
The amount of gaps in forest canopy is related to the radiation interception for photosynthesis and visibility through the canopy. The dependence of forest canopy gap fraction determination on view zenith angle was calculated from polar-transformed sparse ([Formula: see text]) airborne laser scannin...
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| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Taylor & Francis Group
2025-12-01
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| Series: | European Journal of Remote Sensing |
| Subjects: | |
| Online Access: | https://www.tandfonline.com/doi/10.1080/22797254.2025.2456629 |
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| Summary: | The amount of gaps in forest canopy is related to the radiation interception for photosynthesis and visibility through the canopy. The dependence of forest canopy gap fraction determination on view zenith angle was calculated from polar-transformed sparse ([Formula: see text]) airborne laser scanning (ALS) point clouds for a Scots pine (Pinus sylvestris L.) stand growing on Kiriku Bog, Estonia. Visibility of ground targets was estimated from video image frames taken during drone (UAV) overpass at low altitude (40 m). Below-canopy digital hemispherical images (DHP) were taken in zenith direction as reference measurements. Angular grids of 3[Formula: see text] and 5[Formula: see text] were used to match the three data sources so as to decrease uncertainties in measurement geometries. The linear relationship between DHP and UAV data had [Formula: see text] = 0.67, with most of the deviations occurring at gap boundaries. Relationships over individual targets between DHP and polar-transformed ALS data had [Formula: see text]. However, the simulation overestimated gap fraction at smaller zenith angles because of uncertainties in constructing lidar pulse footprints from point data. We conclude that regional coverage by means of sparse ALS point clouds shows potential for the assessment of forest canopy gaps at off-nadir angles. |
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| ISSN: | 2279-7254 |