| Estimating leaf area index of cotton canopy by hyperspectral reflectance in Weibei plateau |
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| DOI：10.7606/j.issn.1000-7601.2017.01.18 |
| Key Words: cotton leaf area index hyperspectrum vegetation index |
| Author Name | Affiliation | | QI Yan-bing | College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China | | CHU Wan-lin | College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China | | XIE Fei | College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China | | CHEN Yang | College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China | | CHANG Qing-rui | College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China |
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| Abstract: |
| Leaf Area Index (LAI) is an important parameter to assess the growth situation of cotton. In this paper, canopy hyperspectral reflectance and LAI were measured at six growth stages of cotton in a field experiment. The correlation of LAI with the original spectral reflectance, the first derivative spectral reflectance, commonly used spectral variables and vegetation index were analyzed. The estimation models of LAI were established using linear regression and multiply stepwise regression methods, and the predictive precision was analyzed. The results indicated that spectral reflectance of cotton canopy decreased gradually with the advance of the growth stage and increase of nitrogen fertilizer application in the visible band, while it was increased from the seeding stage to the flowering and ball stage and it was decreased from the flowering and ball stage to the ball opening stage in the infrared band. The correlation coefficient of LAI with the common used spectral variables and vegetation index were higher in the whole growth stage than the different stages. The maximum correlation coefficients of LAI occurred at the reflectance bands of 1 461 nm with the r=-0.726, while the highest correlation coefficients between the first derivative spectral data and LAI occurred at band of 742 nm with r=0.744. The model based on the first derivative spectral reflectance by using multiply stepwise regression method obtained the most satisfied results for the estimation of LAI in the 742 nm, RMSE=0.94, RE=26.27%, r=0.78. It is feasible to monitor the cotton growth by the first derivative spectral reflectance based on data of the whole growth stage. But for the different regions, the estimating models should be assessed carefully based on plenty of experiments. |
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