Comparaison de méthodes optiques pour estimer l’ouverture de la canopée et l’indice foliaire en forêt feuillue

Soudani, Kamel; Trautmann, Jean; Walter, Jean-Michel

doi:10.1016/s0764-4469(00)01294-4

Cited by 8 publications

(4 citation statements)

References 37 publications

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“…Gap fraction is the fraction of open sky (range 0-1) to a view direction (zenith angle h, azimuth angle Q), or the probability of non-interception P 0 (h, Q) of a ray of light passing through the canopy to that direction. Canopy openness (CO) measures the fraction of sky visible through the canopy, as related to the surface of the hemisphere (Mitchell and Whitmore 1993, ter Steege 1997, Frazer et al 1997, Walter 1999-2001. It is calculated as a percentage as CO%=100 SN…”

Section: Theory and De Nitionsmentioning

confidence: 99%

“…Thus, a range from 0°to 90°zenith angles was considered for the analysis. A total of 167 photographs yielded gap fraction data, which were used as input to CIMES software (Walter 1999(Walter -2001. The value of 0.5 has been chosen for G(h), assuming a spherical distribution of foliage angles.…”

Section: Photographi C Data Acquisition and Exploitationmentioning

confidence: 99%

“…For example, the 'logarithmic averaging method' (also known under the term ' nite length averaging method'), based on the contact number and G-function approach Xiang 1986, Lang 1987), is easy to implement in analyses of hemispherical photographs. Details can be found in Soudani (1999) and Soudani et al (2001). These principles were applied (Walter 1992, unpublished ) to a 34-year old closed Scots pine stand at Hartheim, Bade-Wü rttemberg, Germany, where Heiderich (1989 ) found LAI=3.8 on a projected basis, using a destructive direct method.…”

Section: Eaf Area Indexmentioning

confidence: 99%

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Leaf area index and canopy stratification in Scots pine ( Pinus sylvestris L.) stands

Soudani¹,

Trautmann²,

Walter³

2002

International Journal of Remote Sensing

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In order to assess the contribution of each layer to eVective leaf area index (LAI) in strati ed forest canopies, two Scots pine stands were selected in Haguenau forest, Alsace, France. One stand, 80 years old, had a sparse tree layer and a dense herb layer. The other stand, 50 years old, had a closed tree layer and dense herb and shrub layers. Hemispherical photographs, taken at 10-metre intervals along transects beneath each layer, were digitized and analysed. In the two-layered stand, mean LAI was 0.9 for herbs and 1.5 for trees, contributing 37% and 63%, respectively, to total LAI. A positive and signi cant correlation was found between layers, suggesting that the herb layer had not yet adjusted to the recent thinning of the stand. In the three-layered stand, mean LAI was 1.1 for herbs, 0.4 for shrubs and 2.1 for trees, a contribution of 31%, 11% and 58%, respectively, to total LAI. The positive and signi cant correlation for LAI among layers may be explained by the presence of a mixture of light demanding and shade-tolerant species in the undergrowth. Horizontal spatial auto-covariance of estimates was not signi cant, denoting adequate sampling interval for statistically independent measurements. Such in situ assessments of LAI, diVerentiating vegetation strata, are useful from the perspective of remote sensing of forests, since undergrowth plays an important role in the integrated spectral response of whole canopies.

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Section: Theory and De Nitionsmentioning

confidence: 99%

Section: Photographi C Data Acquisition and Exploitationmentioning

confidence: 99%

Section: Eaf Area Indexmentioning

confidence: 99%

See 1 more Smart Citation

Leaf area index and canopy stratification in Scots pine ( Pinus sylvestris L.) stands

Soudani¹,

Trautmann²,

Walter³

2002

International Journal of Remote Sensing

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“…The LAI is defined as the total leaf area per unit ground area. It provides information that is crucial for understanding photosynthesis, evapotranspiration, primary production, mass, and energy exchanges at different scales (Soudani et al., 2001). The LAI is a key variable that is strongly associated with crop canopy, crop growth, light energy interception, and grain yield (Huang et al., 2016; Towers et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

Unmanned aerial vehicle imagery prediction of sorghum leaf area index under water stress, seeding density, and nitrogen fertilization conditions in the Sahel

Dembele,

Gano,

Mbaye

et al. 2024

Agronomy Journal

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Sahelian Africa must meet the challenge of providing enough food to meet its growing population. Therefore, novel breeding and intensive production methods are needed to mitigate this challenge. The objective of this study was to calibrate and validate sorghum varieties leaf area index (LAI) values estimated from Unmanned Aerial Vehicle (UAV) at different growing seasons in Senegal and Mali. To achieve this objective, four experiments were conducted with 14 sorghum (sorghum bicolor) varieties between 2017 and 2019. At the study sites, LAI was measured and crop reflectance was measured with a multispectral camera mounted on a UAV. The study showed that normalized difference vegetation index (NDVI) and simple ratio (SR) were highly correlated to the area index. The results of validation model revealed a better prediction of measured LAI from NDVI (R2 = 0.92) and SR (R2 = 0.89) vegetation indices in 2019 dry season in Senegal. In addition, the LAI predictions for Mali from NDVI (p < 0.01) and SR (p < 0.01) were highly correlated. Findings showed that vegetation indices can be used to estimate LAI in Mali and Sahel.

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Estimating leaf area index in different types of mature forest stands in Switzerland: a comparison of methods

2010

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Leaf area index (LAI) was estimated at 15 sites in the Swiss Long-Term Forest Ecosystem Research Programme (LWF) in 2004-2005 using two indirect techniques: the LAI-2000 plant canopy analyzer (Licor Inc.) and digital hemispherical photography, applying several exposure settings. Hemispherical photographs of the canopy were analysed using Hemisfer, a software package that offers several new features, which were tested here: (1) automatic thresholding taking the gamma value of the picture into account;(2) implementation of several equations to solve the gapfraction inversion model from which LAI estimates are derived; (3) correction for ground slope effects, and (4) correction for clumped canopies. In seven broadleaved stands in our sample set, LAI was also estimated semidirectly from litterfall. The various equations used to solve the gap-fraction inversion model generated significantly different estimates for the LAI-2000 measurements. In contrast, the same equations applied in Hemisfer did not produce significantly different estimates. The best relationship between the LAI-2000 and the Hemisfer estimates was obtained when the hemispherical photographs were overexposed by one to two stops compared with the exposure setting derived from the reading of a spotmeter in a canopy gap. There was no clear general relationship between the litterfall and the LAI-2000 or the hemispherical photographs estimates. This was probably due to the heterogeneity of the canopy, or to biased litterfall collection at sites on steep slopes or sites subject to strong winds. This study introduces new arguments into the comparison of the advantages and drawbacks of the LAI-2000 and hemispherical photography in terms of applicability and accuracy.

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Comparaison de méthodes optiques pour estimer l’ouverture de la canopée et l’indice foliaire en forêt feuillue

Cited by 8 publications

References 37 publications

Leaf area index and canopy stratification in Scots pine ( Pinus sylvestris L.) stands

Leaf area index and canopy stratification in Scots pine ( Pinus sylvestris L.) stands

Unmanned aerial vehicle imagery prediction of sorghum leaf area index under water stress, seeding density, and nitrogen fertilization conditions in the Sahel

Estimating leaf area index in different types of mature forest stands in Switzerland: a comparison of methods

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