The effect of soil moisture on the reflectance spectra correlations in beech and sessile oak foliage

Reflectance inten sities of foliage are mostly due to bio materials synthesised by plant s . A daptation to the continuously changing environment requires the regulated alteration of m etabolic processes, which also influences the UV - VIS (Ultraviolet - Visible) and IR (Infra Red) spectra of leaves . For the calculation of various Vegetation Indices (VIs), e.g. NDVI (Normalized Difference Vegetation Index) , t he common practice is to use the reflectance spectrum of the whole foliage and when individual leaves of th e same plant are sampled , an average VI is derived . On the contrary , our method exploits the small differences between individual leaves of the same plant , making use of the similar distribution s of measured reflectance values . Using particular wavelength pairs, l inear regressions of reflectance intensities have been investigated . T he parameters of th ese regression s (slope and intercept) have been compared to the temporal variations of the environmental factors, such as temperature, vapour pressure deficit a n d soil moisture . By assessing the sensitivity of the regression coefficient (slope) to the changing environment , wavelength pairs can be selected whose sensitivity change reflect s the effect of soil moisture deficit on the plant . B ased on the state - dependent correlations of the reflectance spectra of plant foliage , a new concept is presented that is capable of indicating the level of environmental stress, e.g. drought stress.