More detailed information about this application is published in: Tichý L., 2016, Field test of canopy cover estimation by hemispherical photographs taken with a smartphone. Journal of Vegetation Science, 27: 427-435.
Canopy Cover (Tree-Layer Cover) is the perpendicular projection of tree (and shrub) crowns onto a horizontal surface is called as canopy cover. Estimation of canopy cover by visual observation is widely used for description of vegetation structure in phytosociology and forest ecology.
Canopy Cover Index is the index used for more precise, non-unbiased estimation of canopy cover for sample plots used in phytosociology and community ecology vegetation survey. Hemispherical photograph is taken from one distinct position. Therefore, the raw fraction of dark pixels within some area represents real tree-layer cover only in limited central part of the photograph near a the zero zenith angle. Greater reduction of gap sizes and light intensity is usually found within increasing zenith angles. If we assume that the vegetation density is constant, the perpendicular projection of tree crowns to horizontal surface from any direction can be estimated as an exponential function of the cosine of the zenith angle (cos alpha). The light incoming from higher zenith angles lowers the precision of canopy cover estimation. Therefore, the weight of canopy cover calculated for partial area i is lower with increasing zenith angle (cos alpha).
The user of the GLAMA software must define, (1) which type of geometric lens distortion is used in a camera, (2) which is the minimum zenith angle of photograph edges and (3) which is a perimeter size (in pixels) of the whole hemisphere.
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Downloads: 86 | ||||
Updated At: 2024-04-23 10:00:04 | ||||
Publisher: LubomÃr Tichý | ||||
Operating System: Android | ||||
License Type: Free |