Spectral reflectance patterns and seasonal dynamics of common understory types in three mature hemi-boreal forests

Due to the growing demand on more accurate prediction of biophysical properties (e.g., leaf area index) or carbon balance models based on remotely sensed data, the understory effect needs to be separated from the overstory. Reflectance models can provide possibility to model and retrieve understory reflectance over large scales, but ground truth data is needed to validate such models and algorithms. In this study, we documented the seasonal variation (April-September) and spectral changes occurring in understory layers of a typical European hemi-boreal forest. The understory composition was recorded and its spectra measured with an ASD FieldSpec Hand-Held UV/VNIR Spectroradiometer eight times at four site types during the growing period (from May to September) in 2013. The collected dataset presented within this study would be of much use to improve and validate algorithms or models for extracting spectral properties of understory from remote sensing data. It can be also further used as a valuable input in radiative transfer simulations that are used to quantify the roles of forest tree layer and understory components in forming a seasonal reflectance course of a hemi-boreal forest, and the upcoming phases of the RAdiation Model Intercomparison (RAMI) experiment.