基于QA权重NDVI时间序列重建效果评价研究——以长江流域为例

Evaluation of Reconstruction Effect of NDVI Time Series Based on QA Weight:A Case Study of MODIS NDVI in the Yangtze River Basin

通过计算质量频率和噪声比分析了长江流域MODIS NDVI质量情况,然后基于常用的S-G、A-G、D-L这3种重建方法设计了3种质量权重方案,对长江流域2001—2020年的时间序列MODIS NDVI数据进行重建,最后采用视觉对比、优质区域保真性和模拟加噪的方法对重建效果进行分析评价。结果表明:长江流域全年噪声比主要集中于75%~125%,其中冬季噪声对NDVI有较大的抑制效果,春秋季其次,而夏季噪声对NDVI有增强效果;基于质量权重方案三的S-G法对原始数据连续缺失的重建效果最好;在高质区域A-G法重建保真性较高,高质像元的R~2和RMSE均值为0.9489和0.0245;在模拟加噪实验中,S-G法重建后数据丢失像元最少,与原始数据的R~2平均值和标准差分别为0.8616和0.1848,RMSE为0.0035~0.4411,标准差为0.0383,表明在低质区域S-G法重建保真性较高。

In this article, the quality of MODIS NDVI in the Yangtze River Basin is analyzed by calculating the mass frequency and noise ratio. Based on three commonly used reconstruction methods of S-G, A-G and DL, three quality weight schemes are designed to reconstruct the time series MODIS NDVI data of the Yangtze River Basin from 2001 to 2020. Subsequently, the reconstruction effect is analyzed and evaluated by visual contrast, high-quality regional fidelity as well as simulation denoising. The results show that the annual noise ratio in the Yangtze River Basin is mainly 75%-125%, in which the noise in winter has a great inhibitory effect on NDVI, followed by spring and autumn, and the noise in summer has an increasing effect on NDVI. The S-G method on the basis of the third quality weight scheme exerts the optimal effect on the reconstruction of continuous missing original data. Additionally, in the high-quality region, the fidelity of A-G method is high,and the mean R~2 and RMSE of high-quality pixels are 0.948 9 and 0.024 5, respectively. Moreover, in the simulation denoising experiment, the S-G method has the least data loss pixels after reconstruction, the average value and standard deviation of the R~2 between the reconstructed data and the original data are 0.861 6 and 0.184 8respectively the RMSE is between 0.003 5 and 0.441 1, and the standard deviation is 0.038 3, indicating that the fidelity of the S-G method is higher in the low-quality area.