The pathogenesis of wheat powdery mildew (WPM) is from the bottom to upper layers of the plant, and the vertical observation angle limits the early monitoring of WPM status. Multiangle remote sensing could effectively extract spatial structural information from different plant layers. The objectives of this study were to improve the monitoring accuracy of WPM severity and to screen suitable observation angles by developing a novel vegetation index. The monitoring capacities of the novel parameters [Normalized Powdery Mildew Index (NPMI) and Ratio Powdery Mildew Index (RPMI)] and 14 optimized traditional spectral parameters were compared at 13 observation angles and different angle ranges. The correlation between all spectral parameters and disease severity was superior in the forward observation direction than in the backward observation direction in the principal plane of the Sun, and the correlation between the two observation directions decreased with an increase in observation angle. The new spectral parameter suitable for inversion of disease index was RPMI ( ${R}_{744}/{R}_{762}-0.5 \times R_{710}$ ), and the best optimal observation angle was +10°, with a 0.852 coefficient, which was 31.74% higher than that of the two-band spectral parameter, ${R}_{744}/{R}_{762}$ . The fitting accuracy of the new parameter in the range of 0° to +30° in the forward direction was 0.704. RPMI could not only improve the monitoring accuracy of powdery mildew severity at a single angle but also achieve a more stable monitoring accuracy in the 0° to +30° range in the forward direction, which significantly expands the application scope of remote sensing monitoring and enhances the flexibility of the technology in actual production environments.

中文翻译：

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使用多角度高光谱遥感监测小麦白粉病的严重程度

小麦白粉病（WPM）的发病机制是从植株的底层到上层，垂直观察角度限制了对WPM状态的早期监测。多角度遥感可以有效地提取植物不同层次的空间结构信息。本研究的目的是通过开发新的植被指数来提高 WPM 严重程度的监测精度并筛选合适的观测角度。在13个观察角度和不同角度范围比较了新参数[标准化白粉病指数（NPMI）和比例白粉病指数（RPMI）]和14个优化的传统光谱参数的监测能力。所有光谱参数与疾病严重程度的相关性在太阳主平面前向观测方向优于后向观测方向，并且两个观测方向之间的相关性随着观测角度的增加而降低。适合疾病指数反演的新光谱参数为RPMI（${R}_{744}/{R}_{762}-0.5 \times R_{710}$），最佳最佳观测角度为+10° ，系数为 0.852，比双波段谱参数 ${R}_{744}/{R}_{762}$ 高 31.74%。新参数在正向0°到+30°范围内的拟合精度为0.704。