Abstract：Pine wilt disease is a devastating disease of pine tree species, thus, early diagnosis of forest pests and diseases in small forest lands even single wood level is particularly important for forest resources protection and sustainable development. This study used black pine as the research object and the multi-angle hyperspectral data from specific black pines canopy were collected through different infected periods, then, we analyzed the spectral characteristics by directional reflectance. The main results were as follows: (1) the reflectance of the backward scattering direction was greater than that of forward scattering direction in theprincipal plane when viewed from the top, in addition, in the backward scattering direction, during the four periods of infection, the four bands had hotspot effect at about 40° of zenith angle. Both in the principal plane and theorthogonal principal plane, the reflectance of pine canopy in the blue wavelengths (450 nm) and the near infrared wavelengths (810 nm) showed a change rule at the azimuth angle of 0°, that were, the early>the health>the metaphase>the end, the red light band (680 nm) and the green light band (560 nm) were the early≈the health>the metaphase≈the end. At all azimuth angles; the canopy reflectivity increased with the increase of observed zenith angle. (2) on upward observation, the reflectance of the forward scattering direction was greater thanthat of the backward scattering direction in the principal plane, in other words, the reflectance was bigger when the azimuth angle was 0°; Both in the principal plane and theorthogonal principal plane, the blue light band (450 nm) and the red light band (680 nm) and the green light band of pine canopy reflectance in azimuth angle were 0°, presenting the early>the health>the end>the metaphase, and the near infrared wavelengths (810 nm) is the early>he health>the metaphase>the end; For all azimuth angles, canopy reflectance decreased with the increase of observed zenith angle. (3) the anisotropy of the bidirectional reflectance of each feature band was the strongest in the principal plane and was the weakest in the main vertical plane, and the forward and backward reflectance of the main vertical surface presented symmetry, namely “mirror reflection”; the reflectance of the canopy of black pine changed significantly with the observed zenith angle at the end of infection period, while it did not change significantly with the observed zenith Angle in other periods. The reflection characteristics of the canopy at different bands and angles can promote the accuracy and reliability of UAV remote sensing to monitorforest diseases at different scales, also promote the construction of portable and real-time diagnosis system for forest diseases, and achieve the rapid acquisition of hyperspectral data at single wood level.
Key words：Multi-angle; Hyperspectral; Directional characteristics; Pine wilt disease; Black pine
夏秀丽，潘 洁，高晓倩，吴辰辰. 黑松冠层反射光谱方向特征分析[J]. 光谱学与光谱分析, 2019, 39(08): 2540-2545.
XIA Xiu-li, PAN Jie, GAO Xiao-qian, WU Chen-chen. Analysis of the Directional Characteristics of the Reflection Spectrum of Black Pine Canopy. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2019, 39(08): 2540-2545.
