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  • Title: [Study on hyperspectral estimation model of crop vegetation cover percentage].
    Author: Zhu L, Xu JF, Huang JF, Wang FM, Liu ZY, Wang Y.
    Journal: Guang Pu Xue Yu Guang Pu Fen Xi; 2008 Aug; 28(8):1827-31. PubMed ID: 18975813.
    Abstract:
    In order to boost the study and application of hyperspectral remote sensing for the estimation of crop vegetation coverage percentage, an ASD FieldSpec Pro FRTM spectroradiometer was used for canopy spectral measurements of rape, corn and rice at different vegetation cover levels and photos of individual plants were taken simultaneously in order to calculate the vegetation cover percentage in computer. Firstly, data of three crops respectively and the mixed data of them were used to make correlation analysis between vegetation coverage percentage and reflectance spectra There was a high correlation between them and no obvious difference in correlation coefficient among different types of crop in the region of blue, red and near-infrared band. This indicated that it was feasible to make correlation analysis and build estimation model using mixed data Secondly, mixed data were used as unique analytical data to calculate red edge variables and pair combination of bands in the region of blue, red and near-infrared band was used to calculate normal difference vegetation index (NDVI). Hyperspectral estimation models with NDVI and red edge variable as independent variable were built individually. The correlation coefficient of the former was larger than the latter, which indicated that NDVI was most effective for the estimation of vegetation coverage percentage. Effective wavelength combinations of NDVI for vegetation cover percentage estimation were determined based on the principle of higher correlation coefficient. NDVI combined with bands in the regions from 350 to 590 nm and from 710 to 1150 nm or bands in the regions from 590 to 710 nm and from 710 to 1300 nm are most effective for vegetation coverage percentage estimation. The best estimation model is simple quadratic equation using NDVI(696-921) as independent variable. The correlation coefficient matrix shows that most of the correlation coefficients of vegetation coverage percentage and NDVI combined with bands in the regions from 630 to 690 nm and from 760 to 900 nm are larger than 0.8. These two band regions correspond to TM3 and TM4 of landsat 4,5,7. It proves that NDVI(TM3-TM4) can be used to and has been used to simulate vegetation coverage percentage. In order to further the study, TM3 and TM4 of Landsat5 was modeled according to spectral response function to calculate NDVI. Correlation analysis was made with NDVI and corresponding vegetation coverage percentage. The correlation coefficient of them was 0.80 and the regression equation was verified by experimental data. This is exploratory research for the calculation of vegetation coverage percentage using TM data in large area.
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