松萎蔫病是松属树种的一种毁灭性病害, 小范围甚至单木水平的森林病虫害的早期诊断对森林资源保护与可持续发展尤为重要。 以感染松萎蔫病的黑松为研究对象, 通过采集不同感病时期的黑松冠层的多角度光谱数据, 分析不同特征波段的方向反射特征, 总结不同感病程度黑松的冠层特征波段反射率的变化规律。 结果显示: (1)在俯视观测时, 在主平面方向的后向散射方向的反射率大于前向散射方向的反射率, 并且在后向散射方向, 四个波段的四个感病时期约在40°的观测天顶角出现热点效应; 无论在主平面还是主垂面, 蓝光波段(450 nm)与近红外波段(810 nm)的黑松冠层0°天顶角反射率呈现出感病初期>健康>感病中期>感病末期的变化规律, 红光波段(680 nm)和绿光波段(560 nm)的黑松冠层0°天顶角反射率呈现出健康≈感病初期>感病中期≈感病末期的变化规律。 在所有方位角, 冠层反射率随着观测天顶角的增加而增大。 (2)在仰视观测时, 在主平面方向的后向散射方向的反射率小于前向散射方向的反射率, 并且在方位角为0°时, 4个波段反射率都是较大的; 无论在主平面还是主垂面, 蓝光波段(450 nm)绿光波段(560 nm)和红光波段(680 nm)的冠层反射率的大小呈现出感病初期>健康>感病末期>感病中期的变化规律, 近红外波段(810 nm)冠层反射率的大小呈现出感病初期>健康>感病中期>感病末期的变化规律; 在所有方位角, 冠层反射率随着观测仰角的增加而减小。 (3)黑松冠层反射光谱在俯视和仰视观测时, 各个特征波段的二向性反射率的各向异性最强的是主平面, 最弱的是主垂面, 且主垂面的前向和后向反射率会呈现对称性, 即“镜面反射”; 各个特征波段在感病末期, 黑松冠层反射率随观测天顶角的变化幅度较大, 其他几个时期反射率随观测天顶角的变化幅度不明显。 研究结果显示的树冠的不同角度的波段反射方向性特征为以后不同尺度的无人机监测的准确性与可靠性奠定基础, 也为发展近地面便携式森林病虫害实时监测系统打下了基础。

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.