Inversion of gap frequency data in forest stands

Nilson, Tiit

doi:10.1016/s0168-1923(99)00114-8

Cited by 158 publications

(97 citation statements)

References 21 publications

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“…This variable is strongly required for accurate modelling of leaf area index L using radiative transfer theory (Majasalmi et al 2014;Nilson 1999;Nilson and Kuusk 2004). In addition, canopy cover is a major determinant of forest reflectance from optical remote sensing data (Dawson et al 1999).…”

Section: Introductionmentioning

confidence: 99%

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A note on estimating canopy cover from digital cover and hemispherical photography

Chianucci¹

2016

Silva Fenn.

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A note on estimating canopy cover from digital cover and hemispherical photography Chianucci F. (2016). A note on estimating canopy cover from digital cover and hemispherical photography. Silva Fennica vol. 50 no. 1 article id 1518. 10p. Highlights• Comparison of fisheye (DHP) and cover (DCP) photography for estimating canopy cover.• Digital photographic estimates validated against artificial images with known cover.• Accuracy of cover estimates from DHP is influenced by mean gap size and actual cover.• Accuracy of cover estimates from DCP is not influenced by mean gap size and actual cover. AbstractFast and accurate estimates of canopy cover are central for a wide range of forestry studies. As direct measurements are impractical, indirect optical methods have often been used in forestry to estimate canopy cover. In this paper the accuracy of canopy cover estimates from two widely used canopy photographic methods, hemispherical photography (DHP) and cover photography (DCP) was evaluated. Canopy cover was approximated in DHP as the complement of gap fraction data at narrow viewing zenith angle range (0°-15°), which was comparable with that of DCP. The methodology was tested using artificial images with known canopy cover; this allowed exploring the influence of actual canopy cover and mean gap size on canopy cover estimation from photography. DCP provided robust estimates of canopy cover, whose accuracy was not influenced by variation in actual canopy cover and mean gap size, based on comparison with artificial images; by contrast, the accuracy of cover estimates from DHP was influenced by both actual canopy cover and mean gap size, because of the lower ability of DHP to detect small gaps within crown. The results were replicated in both DHP and DCP images collected in real forest canopies. Finally, the influence of canopy cover on foliage clumping index and leaf area index was evaluated using a theoretical gap fraction model. The main findings indicate that DCP can overcome the limits of indirect techniques for obtaining unbiased and precise estimates of canopy cover, which are comparable to those obtainable from direct, more labour-intensive techniques, being therefore highly suitable for routine monitoring and inventory purposes.

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Section: Introductionmentioning

confidence: 99%

“…Results from both photographic methods were also compared in real forest canopies. Finally, the impact of canopy cover on modelling canopy attributes like clumping index and leaf area index was illustrated using a theoretical gap fraction model (Nilson 1999).…”

Section: Introductionmentioning

confidence: 99%

A note on estimating canopy cover from digital cover and hemispherical photography

Chianucci¹

2016

Silva Fenn.

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“…The gap probability for a radiation with zenith angle h to transfer through layer k of the canopy, a k (h), is calculated as (Nilson 1999;Wang 2005):…”

Section: Canopy Gap Probabilitymentioning

confidence: 99%

“…In a recent study, Wang (2005) developed the canopy radiation transfer and surface albedo scheme using the gap probability approach of Nilson (1999) and successive orders of scattering approximation. The model treats canopies as being composed of 3-D crowns and explicitly accounts for the clustering of stands as well as plant tissues.…”

Section: Introductionmentioning

confidence: 99%

Simulation of canopy radiation transfer and surface albedo in the EALCO model

2007

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A new canopy radiation transfer and surface albedo scheme is developed as part of the land surface model EALCO (Ecological Assimilation of Land and Climate Observations). The model uses a gap probabilitybased successive orders of scattering approach that explicitly includes the heterogeneities of stands and crown elements and the radiation multiple scattering. The model uses the optical parameters of ecosystem elements and physically represents ecosystem processes in surface albedo dynamics. Model tests using measurements from a boreal deciduous forest ecosystem show that the model well reproduced the observed diurnal and seasonal albedo dynamics under different weather and ecosystem conditions. The annual mean absolute errors between modeled and measured daily albedo and reflected radiation are 0.01 and 1.33 W m -2 , respectively. The model results provide a quantitative assessment of the impacts of plant shading and sky conditions on surface albedo observed in high-latitude ecosystems. The contribution of ground snow to surface albedo in winter was found to be less than 0.1 even though the canopy is leafless during this time. The interception of snow by the leafless canopy can increase the surface albedo by 0.1-0.15. The model results show that the spectral properties of albedo have large seasonal variations. In summer, the near infrared component is substantially larger than visible, and surface albedo is less sensitive to sky conditions. In winter, the visible band component is markedly increased and can exceed the near infrared proportion under cloudy conditions or when snow exists on the canopy. The spectral properties of albedo are also found to have large diurnal variations under the clear-sky conditions in winter.

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“…In a recent study, Wang (2005) developed the canopy radiation transfer model using the gap probability approach of Nilson (1999) and successive orders of scattering approximation. The model treats canopies as being composed of 3-D stands and explicitly accounts for the spatial heterogeneity of stands as well as clustering of plant tissues.…”

Section: Introductionmentioning

confidence: 99%

Variations of Absorbed Photosynthetically Active Radiation over the Canadian Prairie in 2000-2008

Yang¹,

Wang²,

Trishchenko³

et al. 2012

JAS

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The fraction of absorbed photosynthetically active radiation (fAPAR) determines the absorption of solar radiation by vegetation and controls the ecosystem productivity. In this paper, the fAPAR over the Canadian Prairie eco-zone (hereafter the Prairie) was estimated for 2000-2008 using the 3-D canopy radiation transfer model implemented as part of the Ecological Assimilation of Land and Climate Observations (EALCO) model and the Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensing data. With these estimates, the fAPAR magnitude, spatial distribution, and inter-annual variations due to the impact of climate variations were investigated. It was found that the Prairie-scale average fAPAR during the peak growing season was around 0.56 during the nine study years. The inter-annual variation of fAPAR was significantly related to the climate variations over the region, with precipitation being the most important factor. The severe droughts in 2001 and 2002 over the Prairie resulted in 11.5% and 15.2% reduction respectively compared to the 9-year average fAPAR. The spatial variation of fAPAR over the Prairie was largely determined by vegetation types, growing conditions, soil types, and climate factors such as precipitation and temperature. Among the seven eco-regions in the Prairie, the fAPAR was found to be the highest in Aspen Parkland eco-region, owing to the well-growing trembling aspen, mixed tall shrubs and intermittent fescue grasslands under the conditions of favorable precipitation and fertile black soils. The fAPAR was the lowest in Mixed Grassland eco-region where about half the region was cultivated and the remainder was used for pasture or rangeland. This region had the lowest precipitation (250-350 mm per year) in the Prairie.

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Inversion of gap frequency data in forest stands

Cited by 158 publications

References 21 publications

A note on estimating canopy cover from digital cover and hemispherical photography

A note on estimating canopy cover from digital cover and hemispherical photography

Simulation of canopy radiation transfer and surface albedo in the EALCO model

Variations of Absorbed Photosynthetically Active Radiation over the Canadian Prairie in 2000-2008

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