| Title | Quantifying the effect of canopy architecture on optical measurements of Leaf Area Index using two gap size analysis methods |
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| Author | Chen, J M; Cihlar, J |
| Source | IEEE Transactions on Geoscience and Remote Sensing (Institute of Electrical and Electronics Engineers) vol. 33, issue 3, 1995 p. 777-787, https://doi.org/10.1109/36.387593 |
| Year | 1995 |
| Alt Series | Earth Sciences Sector, Contribution Series 20041281 |
| Publisher | Institute of Electrical and Electronics Engineers (IEEE) |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Saskatchewan; Manitoba |
| Area | Prince Albert; Thompson |
| Subjects | Nature and Environment; Science and Technology; remote sensing; vegetation; optical properties; Leaf Area Index (LAI); TRAC (Tracing Radiation and Architecture of Canopies) |
| Released | 1995 05 01 |
| Abstract | In recent years, the methodology in ground-based optical measurements of leaf area index (LAI) of plant canopies has been substantially improved after the introduction of canopy gap size analysis
methods. In this paper, the two methods by Chen and Black and Chen and Cihlar are compared for four boreal conifer stands located near Prince Albert, Saskachewan, and Thompson, Manitoba, Canada. The data used in the analysis were obtained from a new
sunfleck-LAI instrument, the TRAC (Tracing Radiation and Architecture of Canopies), which measures the photosynthetic photon flux density along transects beneath the overstory at a rate of 100 samples per meter. It is confirmed in this study that the
needle shoots of conifer trees can be treated as the basic foliage units (elements) for radiation interception considerations. The effect of foliage clumping at scales larger than the shoots is quantified using an element clumping index. This is
necessary for indirect measurements of LAI based on the gap fraction principle using optical instruments such as the LI-COR LAI-2000. The values of element clumping index derived from these two methods agree within 17% for all stands investigated.
However, the values obtained using Chen and Black's method are consistently smaller than those calculated using Chen and Cihlar's method. The difference results from a negative bias introduced in the method of Chen and Black which requires the
assumption for a random spatial distribution of foliage clumps (tree crowns). The method of Chen and Cihlar makes no assumption of foliage distribution patterns and is therefore more reliable. Yet, Chen and Black's method allows the derivation of
several canopy architectural parameters which are useful for modelling radiative regimes in forest canopies. It is concluded that for remote sensing and other studies, a large quantity of ground truth LAI data can be acquired quickly and accurately
using a combination of indirect optical measurements by the LAI-2000 for the foliage angular distribution and the TRAC for the foliage spatial distribution. |
| GEOSCAN ID | 218083 |
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