Integrating clumping effects in forest canopy structure: an assessment through hemispherical photographs

Walter, Jean-Michel N.; Fournier, Richard; Soudani, Kamel; Meyer, Edgar F.

doi:10.5589/m03-011

Cited by 67 publications

(31 citation statements)

References 31 publications

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“…There are no priori reasons why this should work since the one pixel gap added is dependent on the pixel resolution of the photograph. Another solution was used by Walter et al (2003) where the segments with no gap were removed from the calculations. We selected our segments to be larger than the segment size for which Van Gardingen et al (1999) found an asymptotic behaviour of their clumping factor to avoid segments with no gaps.…”

Section: Clumping Index From Logarithmic Averagementioning

confidence: 99%

“…Kucharik et al (1997Kucharik et al ( , 1999) used a two-band (visible and near-infrared) digital camera to measure gap fraction and gap size distribution to compute the zenith clumping index by comparing allometric LAI and gap fraction inverted LAI and with the gap size distribution method of Chen and Cihlar (1995a). Walter et al (2003) use different methods to extract clumping index angularly from film-based hemispherical photographs, including a simplified version of Chen and Cihlar's theory. Although simplified, their results are generally similar to the results from Chen and Cihlar (1995a) method used here.…”

Section: Introductionmentioning

confidence: 99%

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

Leblanc

Chen

Fernandes

et al. 2005

Agricultural and Forest Meteorology

388

245

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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) This article is a U.S. government work, and is not subject to copyright in the United States.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. # 2005 Published by Elsevier B.V.

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Section: Clumping Index From Logarithmic Averagementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Leblanc

Chen

Fernandes

et al. 2005

Agricultural and Forest Meteorology

388

245

View full text Add to dashboard Cite

show abstract

“…Different methods of biophysical parameter extraction from hemispherical photographs such as radiometric correction (Kuusk and Paas, 2007), clumping computation (Walter et al, 2003;Leblanc et al, 2005), image segmentation (Wagner and Hagemeier, 2006) and exposure and thresholding techniques (Zhang et al, 2005;Cescatti, 2007) have been investigated thoroughly. However, based on previous work it is clear that, besides the aforementioned techniques, the quality of outcome of hemispherical photography depends on how the topography, and particularly the slope effect, is considered.…”

mentioning

confidence: 99%

Methodology comparison for slope correction in canopy leaf area index estimation using hemispherical photography

Gonsamo¹

2008

Forest Ecology and Management

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“…The threshold intensity value was carefully set to obtain binary images that separated sky from the trees [42]. To obtain the gap fraction of a single tree, the original photograph was simplified into separate trees, i.e., one tree in a photo, as shown in Figure 3.…”

Section: Sampling Design Measurements and Data Processing Of Hemispmentioning

confidence: 99%

“…Van Gardingen et al [41] used the Lang and Xiang finite length averaging method to measure the CI with hemispherical photographs. Walter et al [42] used a gap size accumulation method [18] and the Pielou coefficient of spatial segregation to extract CI from film-based hemispherical photographs. Demarez et al [43] calculated the gap fraction and retrieved the CI for row crops utilizing hemispherical photographs.…”

Section: Introductionmentioning

confidence: 99%

Estimating Savanna Clumping Index Using Hemispherical Photographs Integrated with High Resolution Remote Sensing Images

Fan

Liu

et al. 2017

Remote Sensing

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Abstract:In contrast to herbaceous canopies and forests, savannas are grassland ecosystems with sparsely distributed individual trees, so the canopy is spatially heterogeneous and open, whereas the woody cover in savannas, e.g., tree cover, adversely affects ecosystem structures and functions. Studies have shown that the dynamics of canopy structure are related to available water, climate, and human activities in the form of porosity, leaf area index (LAI), and clumping index (CI). Therefore, it is important to identify the biophysical parameters of savanna ecosystems, and undertake practical actions for savanna conservation and management. The canopy openness presents a challenge for evaluating canopy LAI and other biophysical parameters, as most remotely sensed methods were developed for homogeneous and closed canopies. Clumping index is a key variable that can represent the clumping effect from spatial distribution patterns of components within a canopy. However, it is a difficult task to measure the clumping index of the moderate resolution savanna pixels directly using optical instruments, such as the Tracing Radiation and Architecture of Canopies, LAI-2000 Canopy Analyzer, or digital hemispherical photography. This paper proposed a new method using hemispherical photographs combined with high resolution remote sensing images to estimate the clumping index of savanna canopies. The effects of single tree LAI, crown density, and herbaceous layer on the clumping index of savanna pixels were also evaluated. The proposed method effectively calculated the clumping index of moderate resolution pixels. The clumping indices of two study regions located in Ejina Banner and Weichang were compared with the clumping index product over China's landmass.

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Integrating clumping effects in forest canopy structure: an assessment through hemispherical photographs

Cited by 67 publications

References 31 publications

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

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

Methodology comparison for slope correction in canopy leaf area index estimation using hemispherical photography

Estimating Savanna Clumping Index Using Hemispherical Photographs Integrated with High Resolution Remote Sensing Images

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