Abstract
In mobile terrestrial hyperspectral imaging, individual trees often present large variations in spectral reflectance that may impact the relevant applications, but the related studies have been seldom reported. To fill this gap, this study was dedicated to investigating the spectral reflectance characteristics of individual trees with a Sensei mobile mapping system, which comprises a Specim line spectrometer and an Ibeo Lux laser scanner. The addition of the latter unit facilitates recording the structural characteristics of the target trees synchronously, and this is beneficial for revealing the characteristics of the spatial distributions of tree spectral reflectance with variations at different levels. Then, the parts of trees with relatively low-level variations can be extracted. At the same time, since it is difficult to manipulate the whole spectrum, the traditional concept of vegetation indices (VI) based on some particular spectral bands was taken into account here. Whether the assumed VIs capable of behaving consistently for the whole crown of each tree was also checked. The specific analyses were deployed based on four deciduous tree species and six kinds of VIs. The test showed that with the help of the laser scanner data, the parts of individual trees with relatively low-level variations can be located. Based on these parts, the relatively stable spectral reflectance characteristics for different tree species can be learnt.
Highlights
Accurate and comprehensive perception of individual tree properties is a scientific topic of interest, and the related techniques have recently been highlighted, by the forestry community
The evaluations have validated the feasibility that mobile terrestrial hyperpsectral imaging and laser scanning can be applied for investigation of tree spectral reflectance characteristics
The line spectrometer and laser scanner assumed in this study present relatively low sampling resolutions, the parts of the trees with large spectral reflectance variations can be located
Summary
Accurate and comprehensive perception of individual tree properties is a scientific topic of interest, and the related techniques have recently been highlighted, by the forestry community. A large variety of measurement instruments and data-processing approaches have been developed individually aimed at different tree properties. Hyperspectral imaging tends to be assumed for retrieving tree biochemical properties [3] and laser scanning is often used for reconstructing tree structural geometries [4]. Fusion of hyperspectral imaging and laser scanning has been proposed as a solution as well for the acquisition of more complete tree properties [5]. A brief literature review shows that as an important supplementary plan to aerospace and airborne measurements, terrestrial (i.e., ground-based) investigation can supply a potential way for accurately measuring tree properties
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