纹枯病是水稻的主要病害之一, 其防治对于保证水稻产量、 质量具有重要意义, 以高光谱检测水稻病害得到了广泛应用, 并且高光谱降维是光谱分析的重要环节。 该研究在2019年沈农水稻试验基地获取水稻低空遥感冠层与地面冠层高光谱, 并对其进行以窗口宽度为15和阶数为3的Savitzky-Golay平滑处理和光谱变换(得到原始光谱、 一阶微分光谱和倒数之对数光谱), 分窗口对这3种光谱分别进行Gram-Schmidt变换, 找到投影空间并映射出主基底, 实现高光谱数据降维, 绘制具有显著性概率的主基底, 其极大极小值为特征波段。 此外3种光谱还采用了主成分分析和连续投影法降维。 以降维后的数据与水稻纹枯病病情指数进行支持向量机回归建模, 其中支持向量机回归进行粒子群优化, 并以径向基为核函数, 对比分析了3种降维方式的降维效果。 结果表明: 水稻地面冠层尺度建模效果高于低空遥感尺度建模; 在光谱处理方面, 低空冠层高光谱进行倒数之对数变换效果较好, 地面冠层所得高光谱数据进行一阶微分变换效果较好; 分窗Gram-Schmidt变换算法优于主成分分析和连续投影法; 粒子群算法可以优化支持向量机中的惩罚系数和核函数参数, 提高其反演精度; 无人机低空遥感尺度中, 高光谱进行倒数之对数处理, 以分窗Gram-Schmidt变换降维, 敏感波段为427.3, 539.6, 749.5和825.4 nm, PSO-SVR建模决定系数R²为0.731, 均方根误差RMSE为0.151; 地面冠层尺度中, 高光谱进行一阶微分处理, 以分窗Gram-Schmidt变换降维, 敏感波段为552, 607, 702和730 nm, PSO-SVR模型决定系数R²为0.778, 均方根误差RMSE为0.147。 因此, 高光谱技术可以有效地检测水稻纹枯病, 并且其病情指数可用冠层高光谱进行反演, 分窗Gram-Schmidt变换对于高光谱数据降维有较好的效果, PSO-SVR建模对于水稻纹枯病病情指数的反演有明显提高, 结果可为冠层尺度检测水稻纹枯病与病害发生情况提供一定的理论基础和技术支撑。

Sheath blight is one of the main diseases of rice, whose control is of great significance to ensure rice yield and quality. Hyperspectral detection of rice diseases has been widely adopted in recent years, and hyperspectral dimensionality reduction is an important part of spectral analysis. In this study, the hyperspectral data of low altitude remote sensing canopy and rice ground canopy were obtained in Shenyang Agricultural University rice proving ground in 2019, and were smoothed by Savitzky-Golay with a window width of 15 and order of 3, as well as spectral transformations (original reflection spectrum, first-order differential reflection spectrum and inverse-log reflection spectrum), were carried out. To reduce the dimension of hyperspectral data in these 3 spectra, the split-window Gram-Schmidt transform method was used to find the projection space and map the main substrate, in which the main base with significant probability was drawn, and its maximum and minimum value was the characteristic band. The principal component analysis and successive projections algorithm were also used for dimensionality reduction of three spectra. Dimension-reduced data and rice sheath blight disease index were modeled by support vector machine regression, which was used for particle swarm optimization and radial basis function as the kernel function. The effect of three-dimensionality reduction methods was compared and analyzed. The results showed that the modeling effect of the rice ground canopy scale was better than that of the low-altitude remote sensing scale; in the aspect of hyperspectral data processing, the inverse logarithm transformation effect of low-altitude canopy hyperspectral data was better, and the first-order differential transformation effect of ground canopy hyperspectral data was better; the split-window Gram-Schmidt transformation algorithm was better than principal component analysis and successive projections algorithm; particle swarm optimization could optimize the penalty coefficient and kernel function parameters in SVR, and improve the inversion accuracy; in the low-altitude remote sensing canopy scale, the hyperspectral spectrum was processed by using the inverse logarithm processing and the split-window Gram-Schmidt transform, whose sensitive bands were 427.3, 539.6, 749.5 and 825.4 nm respectively. The determination coefficient R² was 0.731 and RMSE was 0.151 by using the PSO-SVR model; in the ground canopy scale, the hyperspectral spectrum was processed by using the first order differential processing and the split-window Gram-Schmidt transform, whose sensitive bands were 552, 607, 702 and 730 nm respectively. The determination coefficient R² was 0.778 and RMSE was 0.147 by using the PSO-SVR model. In conclusion, rice sheath blight can be effectively detected by hyperspectral technology, and its disease index can be retrieved by canopy hyperspectral analysis. The split-window Gram-Schmidt transform has a good effect on the dimensionality reduction of hyperspectral data. PSO-SVR modeling can significantly improve the inversion of rice sheath blight disease index. The results can provide a theoretical basis and technical support for the detection of rice sheath blight and disease occurrence on the canopy scale.