Internal Reflectance Modelling of Hordeum vulgare Leaves During Drying

Spectral reflectance, or indexes that characterize spectral reflectance at concrete wavelength, is commonly used as an indicator of plant stress, or its photosynthetic apparatus status. In this paper, new leaf optical model is presented. Within this paper, experimental determination of surface and internal reflectance of Spring barley leaves and mathematical-physical modelling of internal reflectance were performed. It was proven that a new proposed theoretical model and the experimental spectra of internal reflectance are strongly correlated. It can be concluded that the total reflectance is not a function of epidermis condition, but it testifies about overall functional condition of Spring barley leaves. 1. Introduction Leaf optical properties are associated with physiological stress, that affects these plants. Stress factors can be different: dehydration, freezing, ozone, diseases, herbicides, intraspecies and interspecies competition, insect, lack of mineral nutrition, high salinity, extreme temperatures, and so forth [1–3]. Reflectance spectrum changes are similar for different plant species [1]. Because of this fact, spectral reflectance, or indexes that characterize spectral reflectance at concrete wavelengths, is commonly used such as reliable indicators of plant condition and/or their photosynthetic apparatus status. The study of spectral characteristics has not only scientific, agricultural, and environmental reasons but it is also important from the economical point of view. The spectral characteristics are predominantly used for detection and prevention of potential stress factors [3, 4]. When the electromagnetic radiation impacts air—leaf interface, three competition processes may occur (absorption, reflection, and transmission). Mathematically, it can be described using (1) as a where is electromagnetic flux that impacts the sample, is wavelength, is reflected radiation to the upper halfspace, is angle of incidence, and is leaf surface anisotropy function. ？？is absorbed radiation and is radiation, which passed through the leaf to the lower halfspace. Let us assume that the radiation is not leaking by leaf sides and the leaf fluorescence is not counted into the energy balance described in (1). If the following variables are assumed: reflectance , absorbance , and transmittance , (1) can be rewritten in the form of Total light intensity reflected from the leaf surface is formed by two components, surface reflectance and internal reflectance . Reflectance (surface and internal) is a function of a wavelength and angle of impact if it is