Abstract
Forest types differ in their hyperspectral anisotropy patterns mainly due to species-specific geometrical structure, spatial arrangement of canopies and subsequent shadow patterns. This paper examines the multi-angular, hyperspectral reflectance properties of typical hemiboreal forests during summer time using three simultaneous CHRIS PROBA (mode 3) scenes and stand inventory data from the Järvselja Training and Experimental Forestry District in southeastern Estonia. We investigated the magnitude and reasons for the differences in the anisotropy patterns of deciduous and coniferous stands at three backward viewing angles. A forest reflectance model (FRT) was used as a tool to provide a theoretical basis to the discussion, and to estimate the directional contribution of scattering from crowns and ground to total stand reflectance for the two forest types. The FRT model simulated successfully the HDRF (hemispherical-directional reflectance factor) curves of the study stands to match those obtained from the CHRIS image, yet it produced a smaller and less wavelength-dependent angular reflectance effect than was observed in the satellite image. The main results of this study provide new information for separating the spectral contribution of the forest floor (or understory layer) from the tree canopy layer: (1) the red edge domain was identified to have the largest contribution from forest understory, and (2) the more oblique the viewing angle, the smaller the contribution from the understory. In addition, coniferous stands were observed to have a specific angular effect at the red and red edge domain, possibly as a result of the hierarchical structure and arrangement of coniferous canopies.
Original language | English |
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Pages (from-to) | 2627-2642 |
Number of pages | 16 |
Journal | Remote Sensing of Environment |
Volume | 112 |
Issue number | 5 |
DOIs | |
Publication status | Published - 15 May 2008 |
MoE publication type | A1 Journal article-refereed |
Funding
Our study was supported by the Academy of Finland (COOLFUTURE project) and the Estonian Science Foundation (grants 6100 and 6812). The image data presented in this paper are derived from the CHRIS instrument, developed by Sira Technology Ltd., with support from the British National Space Centre, mounted onboard the European Space Agency's PROBA-1 platform, and provided by the European Space Agency.
Keywords
- Forest reflectance model
- FRT
- Hemiboreal
- Hyperspectral
- Multi-angular canopy reflectance
- VALERI