Rapid Detection of Nitrogen Content and Distribution in Oilseed Rape Leaves Based on Hyperspectral Imaging
ZHANG Xiao-lei1, 2, LIU Fei2, 3*, NIE Peng-cheng2, 3, HE Yong2, 3, BAO Yi-dan2, 3
1. College of Life Science and Technology, Southwest University for Nationalities, Chengdu 610041, China 2. College of Biosystems Engineering and Food Science, Zhejiang University，Hangzhou 310058, China 3. Cyrus Tang Center for Sensor Materials and Applications, Zhejiang University, Hangzhou 310058, China
Abstract：Visible and near infrared (Vis-NIR) hyperspectral imaging system was carried out to rapidly determinate the content and estimate the distribution of nitrogen (N) in oilseed rape leaves. Hyperspectral images of 420 leaf samples were acquired at seedling, flowering and pod stages. The spectral data of rape leaves were extracted from the region of interest (ROI)in the wavelength range of 380～1 030 nm. Different spectra preprocessing including Savitzky-Golay smoothing (SG), standard normal variate (SNV), multiplicative scatter correction (MSC), first and second derivatives were applied to improve the signal to noise ratio. Among 471 wavelengths, only twelve wavelengths (467，557，665，686，706，752，874，879，886，900，978 and 995 nm) were selected by successive projections algorithm(SPA) as the effective wavelengths for N prediction. Based on these effective wavelengths, partial least squares(PLS) and least-squares support vector machines (LS-SVM) calibration models were established for the determination of N content. Reasonable estimation accuracy was obtained, with RP of 0.807 and RMSEP of 0.387 by PLS and RP of 0.836 and RMSEP of 0.358 by LS-SVM, respectively. Considering the simple structure and satisfying results of PLS model, SPA-PLS model was used to generate the distribution maps of N content in rape leaves. The concentrations of N were calculated at each pixel of hyperspectral images at the selected effective wavelengths by inputting its corresponding spectrum into the established SPA-PLS model. Different colour represented the change in N content in the rape leaves under different fertilizer treatments. By including all pixels within the selected ROI, the average N status can be displayed in more detail and visualised. The visualization of N distribution could be helpful to understanding the change in N content in rape leaves during rape growth period and facilitate discovering the difference of N content within one sample as well as among the samples from different fertilising plots. The overall results revealed that hyperspectral imaging is a promising technique to detect N content and distribution within oilseed rape leaves rapidly and nondestructively.
Key words：Hyperspectral imaging;Oilseed rape (Brassica napus L.);Distribution of nitrogen;Partial least square;Successive projections algorithm
张筱蕾1, 2，刘 飞2, 3*，聂鹏程2, 3，何 勇2, 3，鲍一丹2, 3 . 高光谱成像技术的油菜叶片氮含量及分布快速检测 [J]. 光谱学与光谱分析, 2014, 34(09): 2513-2518.
ZHANG Xiao-lei1, 2, LIU Fei2, 3*, NIE Peng-cheng2, 3, HE Yong2, 3, BAO Yi-dan2, 3 . Rapid Detection of Nitrogen Content and Distribution in Oilseed Rape Leaves Based on Hyperspectral Imaging . SPECTROSCOPY AND SPECTRAL ANALYSIS, 2014, 34(09): 2513-2518.
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