The influence of the growing season on the spectral reflectance properties of forest tree species

The aim of current study was to investigate the spectral separability trends of different tree species due to varying foliage spectral reflectance properties during the growing season. Five tree species prevailing in Lithuania were chosen for the study: Aspen (Populus Tremula L.), Black Alder (Alms Glutinosa (L.) Gaertn.), Norway Spruce (Picea Abies L.), Scots Pine (Pinns Sylvestris L.) and Silver Birch (Betula Pendula Roth). The hyperspectral reflectance data was collected under laboratory conditions scanning the foliage samples from two healthy middle aged stands. Hyperspectral scanning was implemented using Themis Vision Systems LLC VNIR 400H hyperspectral imaging camera in 400-1000 nm range. Principal component analysis and the Jeffries-Matusita distance measure were applied for the analysis of hyperspectral data. The wavelengths providing the best separability between tree species were determined. They were discovered to vary during the growing season: in late spring - early summer the most informative wavelengths were concentrated in blue and near infrared spectral zones, in summer they shifted towards green and red zones, and in autumn they moved further to longer waves - the red and near infrared - spectral zones. The investigated tree species were determined to be spectrally separable during the whole growing season, but the particular periods were revealed to contribute for improved spectral separability between certain tree species. The separability between coniferous species was best in September, while deciduous species were best separable when the samples were collected in AugustVytauto Didžiojo universitetasŽemės ūkio akademij