Modern satellite and airborne optical images have increasingly higher resolutions and enable the study of all layers of forests, not just the forest canopy. To understand the contribution of different types of understory on the overall spectral reflectance signal, ground reference data are needed from different types of forests. In this paper, we present the analysis of spectral reflectance factors (350-2300 nm) and fractional covers of understory from 36 boreal forest stands. The data were collected during peak growing season in a southern boreal forest area in Finland. The study stands represent four different forest site fertility types. We used a spectrometer to measure understory spectra in nadir and vegetation quadrats to estimate fractional cover. We showed that the understory has specific spectral features related to the site fertility type and fractional cover. Our results suggest that remote sensing can be used to differentiate forest site fertility types and estimate understory green fractional cover in northern European boreal forests. The collected data are openly available in an open data repository.

现代卫星和机载光学图像的分辨率越来越高，可以研究所有森林层，而不仅仅是森林冠层。为了了解不同类型林下林对整体光谱反射信号的贡献，需要来自不同类型森林的地面参考数据。在本文中，我们对 36 个北方林分的光谱反射系数 (350-2300 nm) 和林下覆盖率进行了分析。这些数据是在芬兰南部北方森林地区的生长高峰期收集的。研究台代表了四种不同的森林场地肥力类型。我们使用光谱仪测量最低点和植被样方中的林下光谱以估计部分覆盖。我们表明林下具有与场地肥力类型和部分覆盖率相关的特定光谱特征。我们的结果表明，遥感可用于区分森林场地肥力类型并估计北欧北方森林的林下绿化覆盖率。收集的数据在开放数据存储库中公开可用。