Understanding the reflectance anisotropy of forests and the underlying scattering mechanisms is needed to improve the accuracy of retrievals of fundamental forest characteristics from optical remote sensing data. In this paper, we developed a laboratory measurement set-up for a large goniometer (LAGOS) and measured multi-angular spectra (350–2500 nm) of 18 small trees, composed of three common European tree species: Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) H. Karst), sessile oak (Quercus petraea (Matt.) Liebl.). For all trees, we measured tree spectra in 47 view angles in the upper hemisphere. To our knowledge, this is the first study reporting multi-angular reflectance spectra of single trees. We also measured the reflectance and transmittance spectra of needles and leaves, as well as reflectance spectra of bark of the sample trees. We analyzed the spectro-directional characteristics of the trees, and the inter- and intraspecific variations of these characteristics. The anisotropy of trees was shown to be strongly asymmetrical and characteristic to species: while pine and spruce exhibited strong hotspot effects, oak showed a strong specular component. Our results indicate that simultaneous measurements of both spectral and directional characteristics of trees may enhance the discrimination of species and thus, support the retrieval of information of their biophysical properties.

需要了解森林的反射各向异性和潜在的散射机制，以提高从光学遥感数据中检索基本森林特征的准确性。在本文中，我们为大型测角仪（LAGOS）开发了实验室测量装置，并测量了18种小树的多角度光谱（350–2500 nm），这些小树由三种欧洲常见树种组成：苏格兰松（Pinus sylvestris L 。），挪威云杉（云杉（Picea abies（L.）H.Karst），无梗橡树（Quercus petraea）（太太）。对于所有树木，我们在上半球的47个视角中测量了树木光谱。据我们所知，这是第一项报告单棵树多角度反射光谱的研究。我们还测量了针叶的反射光谱和透射光谱，以及样品树皮的反射光谱。我们分析了树木的光谱方向特征，以及这些特征的种间和种内变化。树木的各向异性被证明是极不对称的，并且是物种的特征：松树和云杉表现出强烈的热点效应，橡树表现出强烈的镜面反射成分。我们的结果表明，同时测量树木的光谱和方向特征可能会增强物种的区分度，因此，