Abstract

It is shown that the laser and optical nephelometric measurements including the spectropolarizational ones at different angles are highly informative for non-contact plant diagnostics. Before recent time the traditional view on the polarization of plant-reflected radiation was a formation of the polarized component due to a specular reflection on the leaf surface exceptionally. Our detailed studies on the spectral and angular dependences of the reflected light polarization degree for the different plant leaves have shown that the singly and multiply scattering on intraleaf structure elements combined with chlorophyll molecular absorption is very essential for the formation of polarized light component. It is also found that the polarizational characteristics are more sensitive for the changes of plant structure as compared with the traditionally measured bidirectional reflectance factors. We have discovered and theoretically substantiated a spectral shift of a main maximum of the polarization degree angular dependence and an appearance of the additional (non-Brewster) maxima at the incident angles of 65-75°, 15-20°, 30-35° and 40-45°. The features of polarization degree angular function are resulted from single scattering processes and concerned with such factors as intraleaf water concentration, leaf's age, size, and concentration proportions of the lipid and protein components. The experimental and theoretical obtained results give the basis of optical and laser remote diagnostics of the intraleaf structure; in particular, make possible to obtain the refractive indexes of leaf structure elements, intracell particle concentrations, and particle size distribution functions. It is shown that the plant illness (in particular, bacterial cancer), ontogenetic development of plants, and ecological state of vegetation may be diagnosed from analysis of the polarization degree angular functions.

© 1994 IEEE