A coefficient CW, which was defined as the ratio of NIR (near infrared) to the red reflected spectral response of the spectrometer, with a standard whiteboard as the measuring object, was introduced to establish a method for calculating height-independent vegetation indices (VIs). Two criteria for designing the spectrometer based on an active light source were proposed to keep CW constant. A designed spectrometer, which was equipped with an active light source, adopting 730 and 810 nm as the central wavelength of detection wavebands, was used to test the Normalized Difference Vegetation Index (NDVI) and Ratio Vegetation Index (RVI) in wheat fields with two nitrogen application rate levels (NARLs). Twenty test points were selected in each kind of field. Five measuring heights (65, 75, 85, 95, and 105 cm) were set for each test point. The mean and standard deviation of the coefficient of variation (CV) for NDVI in each test point were 3.85% and 1.39% respectively, the corresponding results for RVI were 2.93% and 1.09%. ANOVA showed the measured VIs possessed a significant ability to discriminate the NARLs and had no obvious correlation with the measurement heights. The experimental results verified the feasibility and validity of the method for measuring height-independent VIs.

中文翻译：

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基于有源光源的与高度无关的植被指数的测量方法。

引入系数CW定义为以标准白板为测量对象的NIR（近红外）与光谱仪的红色反射光谱响应之比，以建立计算与高度无关的植被指数（VIs）的方法）。提出了两种基于有源光源的光谱仪设计标准，以保持CW恒定。设计的光谱仪配备有源光源，采用检测波段的中心波长为730和810 nm，用于在两个小麦田中测试归一化植被指数（NDVI）和比率植被指数（RVI）。氮肥施用量水平（NARLs）。在每种领域中选择了20个测试点。为每个测试点设置五个测量高度（65、75、85、95和105厘米）。在每个测试点，NDVI的变异系数（CV）的平均值和标准偏差分别为3.85％和1.39％，RVI的相应结果为2.93％和1.09％。方差分析显示被测VI具有区分NARL的显着能力，并且与测量高度无明显相关性。实验结果验证了该方法的可行性和有效性，该方法用于测量与高度无关的VI。