植被指数反演冬小麦植被覆盖度的适用性研究
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国家自然科学基金资助项目(51179162)、“十二五”国家科技支撑计划资助项目(2011BAD29B01)和高等学校学科创新引智计划资助项目(B12007)


Applicability of Vegetation Indices to Estimate Fractional Vegetation Coverage
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    摘要:

    利用冬小麦2个生长季高光谱反射率和覆盖度实测资料,基于回归分析方法建立4种植被指数反演植被覆盖度模型,并对预测模型年际间的稳定性进行了验证。采用噪声等效覆盖度误差对各植被指数反演植被覆盖度模型进行了敏感性分析,结合对模型的残差分析得到了不同种植密度和氮肥施用量条件下各植被指数的适用性。结果表明:归一化植被指数NDVI和改进的土壤调节指数TSAVI与冬小麦覆盖度采用抛物线拟合结果较好;修正的土壤调节植被指数MSAVI和增强型植被指数EVI与覆盖度符合线性关系。验证模型的决定系数略低于建模方程,反演模型在年际间表现出较好的稳定性,能够满足覆盖度预测需要。NDVI和TSAVI较MSAVI和EVI可更好地解释本地区冬小麦植被覆盖度的变化规律。在低到中覆盖度(0~60%)条件下,如果当地土壤信息可获得,利用植被指数TSAVI估算植被覆盖度变化规律表现出较好的敏感性和较高的估算精度。如果缺失土壤线资料,NDVI能保证覆盖度的估算精度。在高覆盖度(60%~100%)条件下,可选用敏感性和精度均良好的植被指数MSAVI进行估算。在水分供应充分的条件下,4种植被指数对作物种植密度和氮肥施用量均不敏感,可采用统一模型进行不同种植密度和不同施氮量处理的冬小麦覆盖度估算研究,为利用植被指数快捷、准确地估算本地区区域植被覆盖度提供了理论和技术支持。

    Abstract:

    Many linear or non-linear statistics models have been developed for the estimation of fractional vegetation coverage by using vegetation indices. However, as the disturbance by uncertainty factors such as various crop planting density and nitrogen application, vegetation indices are limited to monitor regional vegetation coverage. In this paper, vegetation indices inversion models of fraction vegetation coverage based on regression analysis method were established and evaluated by using observed hyperspectral reflectance and vegetation coverage data set of winter wheat in the year 2010—2011. Firstly, the empirical models’ applicability (sensitivity, interannual stability and accuracy) were analyzed by using noise equivalent and model evaluation parameters. Simulation results indicated that there is a better result of using a second order polynomial regression equation to describe relationships between vegetation indices NDVI (Normalized difference vegetation index), TSAVI (Transformed soil adjusted vegetation index) and fraction vegetation coverage. While vegetation indices MSAVI (Modified soil adjustment vegetation index) and EVI (Enhanced vegetation index) exhibited a linear relationship with various fraction vegetation coverage. Evaluation results showed that: the correlation coefficient of regressed evaluation equations between predicted and measured vegetation coverage (Fc) were a little lower than the former modeling equations. All the evaluation relationships were significant at p=001 confidence level, which indicated these vegetation indices inversion models seemed stable among years and could give simple but reliable estimate of fraction vegetation coverage in this region. Sensitivity analysis suggested that under low to medium coverage (0~60% Fc) conditions, if the local soil information was available, using TSAVI to estimate variation of vegetation coverage showed better performance. However, if there was no information on soil characteristics, NDVI could assure estimation accuracy of fraction vegetation coverage. When vegetation cover Fc>60%, MSAVI was suggested to be used for estimating vegetation coverage, which displayed better sensitivity, stability and accuracy. Then, the general linear model (GLM) was employed to analyze the residuals of empirical models under conditions of various planting densities and nitrogen application rates. The results were somewhat inspiring: under condition of adequate water supply, all four vegetation indices (NDVI, EVI, TSAVI, MSAVI) exhibited no sensitive to various planting densities and nitrogen application rates during the entire growth period of winter wheat. This means models based on these four vegetation indices may not require re parameterization when apply to crops with different planting densities and nitrogen application rates. The regional winter wheat coverage could be directly estimated by using vegetation indices inversion models under the circumstances of abundant water supply. These findings provide a theoretical and technical support for the use of vegetation index to quickly and accurately estimate the regional vegetation coverage. However, as the regional land surface could be various and changeable, this paper could only explain the strength of vegetation indices inversion models for adequate water supply conditions, further studies are required for assessing vegetation indices method applicability in different crop intercropped and water and fertilizer coupling conditions.

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虞连玉,蔡焕杰,姚付启,郑 珍,王 健,李志军.植被指数反演冬小麦植被覆盖度的适用性研究[J].农业机械学报,2015,46(1):231-239.

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  • 收稿日期:2014-03-31
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  • 在线发布日期: 2015-01-10
  • 出版日期: 2015-01-10