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Open AccessArticle

Measurement Method for Height-Independent Vegetation Indices Based on an Active Light Source

1
College of Engineering, Nanjing Agricultural University, Nanjing 210031, China
2
National Engineering and Technology Center for Information Agriculture, Nanjing 210095, China
3
Jiangsu Key Laboratory for Intelligent Agriculture Equipment, Nanjing 210031, China
*
Author to whom correspondence should be addressed.
Sensors 2020, 20(7), 1830; https://doi.org/10.3390/s20071830
Received: 17 December 2019 / Revised: 14 March 2020 / Accepted: 24 March 2020 / Published: 25 March 2020
(This article belongs to the Special Issue Smart Agricultural Applications with Internet of Things)
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. View Full-Text
Keywords: active light source; vegetation indices; reflectance spectrometer; measurement method active light source; vegetation indices; reflectance spectrometer; measurement method
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Ding, Y.; Jiang, Y.; Yu, H.; Yang, C.; Wu, X.; Sun, G.; Fu, X.; Dou, X. Measurement Method for Height-Independent Vegetation Indices Based on an Active Light Source. Sensors 2020, 20, 1830.

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