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    多卫星数据反射率标准化后重建15 m分辨率作物植被指数时间序列

    Reconstruction of vegetation index time-series data for crops at a 15 m resolution after reflectance normalization of multi-satellite data

    • 摘要: 植被指数的变化在一定程度上可以反映所在区域植被覆盖变化及生长情况,通过监测植被指数时间序列的变化对于当地农业管理具有重要意义。现有的植被指数时间序列重建方法存在数据源输入单一、重建结果空间分辨率低等问题。为此,该文提出一种融合卫星数据标准化方法及作物参考曲线法的植被指数时间序列重建方法,重建研究区域冬小麦2021年的高时空分辨率的归一化植被指数(normalized differential vegetation index,NDVI)及增强型植被指数(enhanced vegetation index,EVI)时间序列。结果表明:①反射率标准化后在红光、绿光、红外及近红外波段,GF-1卫星与VIIRS地表反射率数据决定系数(coefficient of determination,R2)大部分提高0.05,少部分提高超过了0.1。均方根误差(root mean square error,RMSE)降低,大部分RMSE降低了0.01,相对均方根误差(relative root mean square error,rRMSE)降低幅度在2%左右。GF-6卫星大部分R2提高了约0.12,RMSE大部分减小了0.03,rRMSE减小幅度普遍在3%~4%之间。Sentinel-2卫星R2整体提升约0.05,RMSErRMSE的降低大部分在0.001及2%左右。②重建的研究区内高分辨植被指数时间序列精度评价结果显示,NDVI时间序列重建结果在验证时期均有较高的R2,大多数验证影像R2达到0.5及以上;RMSE在所有的验证时期均小于0.1。相对误差(relative error,RE)在绝大部分情况下小于15%,仅有1景验证影像RE达到18%。EVI时间序列重建结果同样具有较高的R2,在验证影像中有5景影像的R2不低于0.44,大部分影像RMSErRMSE的值分别小于0.15及20%。

       

      Abstract: Changes in the vegetation index can reflect variations in vegetation cover and growth in the region to some extent. Monitoring the changes in vegetation index time-series data plays a significant role in local agricultural management. However,existing methods for vegetation index time-series data reconstruction face challenges such as a single data source input and low spatial resolution of reconstruction results. In response to this,this paper proposes a reconstruction method for vegetation index time-series data that integrates the satellite data standardization method and the crop reference curve method. Consequently,it reconstructed vegetation index time-series data with high spatiotemporal resolution for winter wheat in the study area in 2021,including normalized differential vegetation index (NDVI) and enhanced vegetation index (EVI). The results show that after reflectance normalization,the coefficient of determination (R2) for GF-1 satellite and VIIRS surface reflectance data in red,green,infrared,and near infrared bands generally increased by 0.05%,with a few exceeding 0.1%. The root mean square error (RMSE) was reduced,with the majority decreasing by 0.01. In contrast,the relative root mean square error (rRMSE) showed a reduction of about 2%. Most data from the GF-6 satellites exhibited an increase of about 0.12 in R2,a decrease of 0.03 in RMSE,and a general decline in rRMSE ranging from 3% to 4%. In contrast,the data from the Sentinel-2 satellite show an overall increase of about 0.05 in R2,as well as a decrease of around 0.001 and 2% in RMSE and rRMSE,respectively. The accuracy assessment results for the reconstructed high-resolution vegetation index time-series data indicate that the NDVI time-series reconstruction results presented high R2 values in the validation period,with five validation images reaching 0.49 and above. The RMSE was less than 0.1 in all validation periods,while the relative error (RE) was less than 15% in most cases,with only one validation image reaching 18%. Similarly,the EVI time-series reconstruction results also exhibited high R2 values,with five validation images above 0.44. Both RMSE and rRMSE values were less than 0.15 and 20%,respectively.

       

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