Methodology comparison for canopy structure parameters extraction from digital hemispherical photography in boreal forests

• Published in: Agricultural and forest meteorology Vol. 129; no. 3; pp. 187 - 207
• Main Authors: Leblanc, Sylvain G., Chen, Jing M., Fernandes, Richard, Deering, Donald W., Conley, Alexis
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 30-04-2005; Oxford Elsevier; New York, NY
• Subjects: Agricultural and forest climatology and meteorology. Irrigation. Drainage; Agronomy. Soil science and plant productions; Biological and medical sciences; boreal forests; Canopy architecture; canopy gaps; digital hemispherical photography; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Hemispherical photography; Leaf area index; leaves; methodology; overstory; photography; solar radiation; stand density; stand structure; TRAC; tree and stand measurements; Canada; Russia; Canopy architecture; Hemispherical photography; TRAC; Leaf area index; Biometeorology; Photography; Boreal forest; Architecture; Methodology; Canopy(vegetation)
• ISSN: 0168-1923; 1873-2240
• DOI: 10.1016/j.agrformet.2004.09.006

The retrieval of canopy architectural parameters using off-the-shelf digital cameras with fish-eye lens is investigated. The technique used takes advantage of the sensor's linear response to light of these cameras to improve the estimation of gap fraction using:
(1)
the digital numbers of mixed sky-canopy pixels to estimate the within-pixel gap fraction; and
(2)
this process is done considering the variation in view zenith angle to take into account the sky radiance distribution and the canopy multiple scattering effects.
The foliage element clumping index is retrieved over a wide range of view zenith angles using:
(1)
the accumulated gap size distribution theory developed for the TRAC by
Chen and Cihlar (1995a);
(2)
the
Lang and Xiang (1986) finite-length averaging method; and
(3)
a method combining the gap size distribution and the Lang and Xiang finite-length methods.
Using data from Canadian and Russian boreal forests, comparisons of gap fraction, clumping index and plant area index measured with the tracing radiation and architecture of canopies (TRAC) and digital hemispherical photography are presented. Evaluation of the LAI estimated from digital hemispherical photography with allometric LAI of two boreal forest stands suggest that that the clumping index combined method may be more accurate.