Abstract
Remote sensing, which is based on a reflected electromagnetic spectrum, offers a wide range of research methods. It allows for the identification of plant properties, e.g., chlorophyll, but a registered signal not only comes from green parts but also from dry shoots, soil, and other objects located next to the plants. It is, thus, important to identify the most applicable remote-acquired indices for chlorophyll detection in polar regions, which play a primary role in global monitoring systems but consist of areas with high and low accessibility. This study focuses on an analysis of in situ-acquired hyperspectral properties, which was verified by simultaneously measuring the chlorophyll concentration in three representative arctic plant species, i.e., the prostrate deciduous shrub <em>Salix polaris</em>, the herb <em>Bistorta vivipara</em>, and the prostrate semievergreen shrub <em>Dryas octopetala</em>. This study was conducted at the high Arctic archipelago of Svalbard, Norway. Of the 23 analyzed candidate vegetation and chlorophyll indices, the following showed the best statistical correlations with the optical measurements of chlorophyll concentration: Vogelmann red edge index 1, 2, 3 (VOG 1, 2, 3), Zarco-Tejada and Miller index (ZMI), modified normalized difference vegetation index 705 (mNDVI 705), modified normalized difference index (mND), red edge normalized difference vegetation index (NDVI 705), and Gitelson and Merzlyak index 2 (GM 2). An assessment of the results from this analysis indicates that <em>S. polaris</em> and <em>B. vivipara</em> were in good health, while the health status of <em>D. octopetala</em> was reduced. This is consistent with other studies from the same area. There were also differences between study sites, probably as a result of local variation in environmental conditions. All these indices may be extracted from future satellite missions like EnMAP (Environmental Mapping and Analysis Program) and FLEX (Fluorescence Explorer), thus, enabling the efficient monitoring of vegetation condition in vast and inaccessible polar areas.
Highlights
Imaging spectroscopy, which consists of recording electromagnetic radiation in hundreds of narrow bands (2–5 nm), makes it possible to analyze how electromagnetic radiation interacts with the analyzed matter [1]
The highest average chlorophyll concentration was found in S. polaris with an average Chl index of 34.1, expressed as μg cm−2 [47]
The lowest average chlorophyll concentration was found in D. octopetala
Summary
Imaging spectroscopy, which consists of recording electromagnetic radiation in hundreds of narrow bands (2–5 nm), makes it possible to analyze how electromagnetic radiation interacts with the analyzed matter [1]. The selective absorption, reflection, or transmission of various wavelengths allows a detailed analysis of the spectral properties of individual plants and vegetation communities [2]. The absorbed radiation is used in photosynthesis and fluorescence processes and is emitted as heat. Spectral characteristics (reflectance in selected wavelengths) are used to calculate remote sensing vegetation indices [12], which use various mathematical combinations of relevant coefficients to identify the analyzed properties of plants. Some plants can modulate light absorption during the process of photosynthesis through the use of mechanisms such as leaf movement, leaf angle adjustments [15], covering the leaves with substances such as wax [16], and changing the concentration of certain pigments, e.g., anthocyanin [17]. These processes complement each other, and the level of each of them depends on the levels of the other two [19]
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