Kuusinen Nea, Juola Jussi, Karki Bijay, Stenroos Soili, Rautiainen Miina
Department of Built Environment, School of Engineering, Aalto University, P.O. Box 14100, FI-00076 Aalto, Finland.
Botany Unit, Finnish Museum of Natural History, P.O. Box 7, FI-00014, University of Helsinki, Finland.
Remote Sens Environ. 2020 Sep 15;247:111955. doi: 10.1016/j.rse.2020.111955.
Lichens dominate a significant part of the Earth's land surface, and are valuable bioindicators of various environmental changes. In the northern hemisphere, the largest lichen biomass is in the woodlands and heathlands of the boreal zone and in tundra. Despite the global coverage of lichens, there has been only limited research on their spectral properties in the context of remote sensing of the environment. In this paper, we report spectral properties of 12 common boreal lichen species. Measurements of reflectance spectra were made in laboratory conditions with a standard spectrometer (350-2500 nm) and a novel mobile hyperspectral camera (400-1000 nm) which was used in a multiangular setting. Our results show that interspecific differences in reflectance spectra were the most pronounced in the ultraviolet and visible spectral range, and that dry samples always had higher reflectance than fresh (moist) samples in the shortwave infrared region. All study species had higher reflectance in the backward scattering direction compared to nadir or forward scattering directions. Our results also reveal, for the first time, that there is large intraspecific variation in reflectance of lichen species. This emphasizes the importance of measuring several replicates of each species when analyzing lichen spectra. In addition, we used the data in a spectral clustering analysis to study the spectral similarity between samples and species, and how these similarities could be linked to different physical traits or phylogenetic closeness of the species. Overall, our results suggest that spectra of some lichen species with large ground coverage can be used for species identification from high spatial resolution remote sensing imagery. On the other hand, for lichen species growing as small assemblages, mobile hyperspectral cameras may offer a solution for in-situ species identification. The spectral library collected in this study is available in the SPECCHIO Spectral Information System.
地衣覆盖了地球陆地表面的很大一部分，是各种环境变化的重要生物指示物。在北半球，最大的地衣生物量存在于北方针叶林带的林地和石南荒原以及苔原地区。尽管地衣分布于全球，但在环境遥感背景下，对其光谱特性的研究仍然有限。在本文中，我们报告了12种常见北方地衣物种的光谱特性。在实验室条件下，使用标准光谱仪（350 - 2500纳米）和新型移动高光谱相机（400 - 1000纳米）进行反射光谱测量，该相机用于多角度设置。我们的结果表明，种间反射光谱差异在紫外和可见光谱范围内最为明显，并且在短波红外区域，干燥样本的反射率总是高于新鲜（潮湿）样本。与天底或前向散射方向相比，所有研究物种在背向散射方向具有更高的反射率。我们的结果还首次揭示，地衣物种的反射率存在很大的种内变异。这强调了在分析地衣光谱时对每个物种测量多个重复样本的重要性。此外，我们将这些数据用于光谱聚类分析，以研究样本和物种之间的光谱相似性，以及这些相似性如何与物种的不同物理特征或系统发育亲缘关系相关联。总体而言，我们的结果表明，一些大面积分布的地衣物种的光谱可用于从高空间分辨率遥感影像中识别物种。另一方面，对于以小群落形式生长的地衣物种，移动高光谱相机可能为现场物种识别提供解决方案。本研究收集的光谱库可在SPECCHIO光谱信息系统中获取。
