Theoretical estimates of sensitivity in some vegetation indices to variation in the canopy condition

Abstract

Based on the Goudriaan (1977) reflectance model, the choice of vegetation indices (VI) was substantiated. The Vis are optimal to reconstruct the key parameter of plant canopy, i.e. the phytoelements' relative surface. The numerical experiment simulated the changes within a wide spectrum of plant colour, spatial orientation of phytoelements and soil brightness. Under analysis were nine combinations of canopy spectral reflectances in the visible and near-infrared wavelength intervals. Among these are indices widely used in practical remote sensing of vegetative targets: the simple ratio (VI₁]), normalized difference (VI₈) and the perpendicular vegetative index (VI₉). The optimal VI_s was chosen by three criteria; (1) stability in tendencies in the VI_s changes as a function of the phytoelements' relative surface, (2) sensitivity of the VI_s to variations in the phytoelements' relative surface and (3) the impact of other parameters on the interdependence between the VI_s and the phytoelements' relative surface. It was discovered that the advantages of VI_s as compared with the canopy spectral reflectance are in the VI_s' ability to improve the informative significance of remote sensing for solving inverse tasks. Using VI₁ VI₈ and VI₉ for defining the relative surface of phytoelements permits one to minimize the impact of soil brightness. It is feasible to employ VI₁ and VI₈ for conditions of space-time variation in the orientation of phytoelements and it is better to use VI₉ for conditions of variation in plant colour.