دانلود رایگان مقاله الزویر درباره برآورد شاخص میزان برگ با تحلیل هیستوگرام (کلیک کنید)
توضیحات :
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مشخصات این مقاله :
عنوان مقاله :
An improved estimate of leaf area index based on the histogram analysis of hemispherical photographs
ترجمه فارسی عنوان :
بهبود برآورد شاخص سطح برگ بر اساس تجزیه و تحلیل هیستوگرام عکس های نیم کره ای
سال انتشار : 2009
متعلق به مجله یا ژورنال : هواشناسی کشاورزی و جنگل (Agricultural and faorest Meteorology)
فرمت: PDF
تعداد صفحات: 9
شماره پروژه: 5006
کلمات کلیدی :
Hemispherical photography, Histogram, Optimal threshold value, Gap fraction, Litterfall, Leaf area index (LAI)
عکاسی نیم کره ای، هیستوگرام، مقدار آستانه بهینه، بخشی از فاصله، شاخص سطح برگ (LAI)
چکیده :
Abstract
Leaf area index (LAI) is a key parameter that affects the surface fluxes of energy, mass, and momentum over vegetated lands, but observational measurements are scarce, especially in remote areas with complex canopy structure. In this paper we present an indirect method to calculate the LAI based on the analyses of histograms of hemispherical photographs. The optimal threshold value (OTV), the gray-level required to separate the background (sky) and the foreground (leaves), was analytically calculated using the entropy crossover method (Sahoo, P.K., Slaaf, D.W., Albert, T.A., 1997. Threshold selection using a minimal histogram entropy difference. Optical Engineering 36(7) 1976–1981). The OTV was used to calculate the LAI using the well-known gap fraction method. This methodology was tested in two different ecosystems, including Amazon forest and pasturelands in Brazil. In general, the error between observed and calculated LAI was 6%. The methodology presented is suitable for the calculation of LAI since it is responsive to sky conditions, automatic, easy to implement, faster than commercially available software, and requires less data storage.
مقدمه این مقاله :
Introduction
Leaf area index (LAI), defined as the one-sided green leaf area per unit ground area (m2/m2) is an important parameter in climate studies and is a key parameter used in land surface parameterizations. Leaf area determines substantially the vegetation–atmosphere exchanges of energy, momentum and mass (Monteith and Unsworth, 1990; Myneni et al., 2007). A reduction in LAI decreases transpiration (Parton et al., 1996), affecting the biochemical and hydrological cycle. Therefore, accurate representation of the seasonality and spatial variability of LAI should improve estimates of surface water balance and productivity (Wright et al., 1996; Huete et al., 2006), and consequently improve estimates of both deforestation and global warming impacts on regional and global climate (Nobre et al., 2004; Costa and Foley, 2000). Direct measurements of LAI are laborious, destructive, and may not represent well the large spatial variability of complex canopy structure (Roberts et al., 1996). The gap fraction method, an indirect approach, has been widely used to estimate LAI (Norman and Campbell, 1989) through the use of belowcanopy
hemispherical images.
توجه :
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دانلود رایگان مقاله الزویر درباره برآورد شاخص میزان برگ با تحلیل هیستوگرام (کلیک کنید)
