А METHOD OF EVALUATING THE ABSORPTION SPECTRUM OF WHEAT LEAF BY THE SPECTRUM OF DIFFUSE REFLECTION

Abstract

Spectral analysis methods are widely used to assess the condition of plants during normal growth and the development of infections. In combination with mathematical methods of pattern recognition from reflection spectra, different indices are constructed, which vary for plants in different studied physiological (and pathophysiological) states. This approach involves setting up indices for specific shared states. Information about the content of pigments is more universal, and allows to talk about the state of the plant on the basis of physiological concepts, regardless of the task being solved. Methods of reflective spectroscopy have recently been developed to obtain information about the content of pigments. The absorption spectrum is estimated from the diffuse reflection spectrum based on the light propagation model in a disperse medium. One of the models of this type is the model Kubelka-Munch. In the case of the large optical thickness of the sample, when the flow passing through the sample at the output is almost zero, one can use a simplified formula, which does not include the thickness of the sample. In other cases, it is necessary to measure this thickness, which is problematic for such biological objects as a plant leaf, because of the complex relief of the leaf surface. The article presents the measurement method and results of studying the applicability of the formula Kubelka-Munch for obtaining absorption spectra from reflection spectra of a wheat leaf without measuring its thickness. The formula is derived for calculation of Kubelka-Munch function (ratio of the absorption coefficient to the diffusion coefficient) by two measurements of diffusion scattering coefficients from the sample, which are performed with absorbing and reflecting substrates. The method allows to calculate the ratio of the absorption coefficient to the diffusion coefficient without measuring the thickness of the sample under study. This index can be used as an assessment criteria of the absorption spectrum with some proportionality factor. It is possible to recommend the method described as the most valid and accurate one for the determination of the absorption coefficient to the diffusion coefficient ratio of a leaf in the laboratory conditions.