THE EFFECT OF SKY OPTICAL RADIATION ON THE MODIFIED LEAF AREA INDEX

Abstract

The leaf area index (LAI) and phytomass are major parameters characterizing net primary production, which could be determined by methods of remote sensing of vegetation crown. LAI expresses interrelation of vegetation crown with optical radiation of the Sun and is very significant parameter for determinatio of of exchange ofСО , H O, and energy between vegetation and atmosphere. LAI is also the quantitative parameter of seasonal 2 2 changes of crown and phenology of vegetation which are admitted as integrated parameters of vegetation reactions on climatic changes. This index quantitatively can be determined both by methods of on-board measurements and methods of ground validation measurements. At the same time, the information derived by help of reflected from vegetation radiation depends on such parameters as the angle of solar elevation, background reflections, intrinsic special parameters of phytomass, and LAI index. The article examines the effect of sky background radiation on a value of the suggested modified index LAI. The carried out model researches showed that non-certainty of the suggested modified leaf area index (MLAI) was minimal upon decreasing type of function of dependence of FAPAR on sky background radiation i.e. upon big zenith angles of the Sun. On the basis of this fact the conclusion was made that the newly suggested index MLAI is most stable upon big zenith angles of the Sun, thus upon presence of data on sky background radiation leaf area index should be calculated using the newly suggested MLAI upon big zenith angles of the Sun.