基于Hyb-F组合滤波算法的向海自然保护区NDVI时间序列重构

doi:10.13229/j.cnki.jdxbgxb20170865

摘要/Abstract

摘要： 针对借助遥感手段直接获取的归一化植被指数(NDVI)时间序列含有噪声数据,而单一应用局部或全局时间序列重构算法不能完全剔除噪声,重构精度受到一定影响的问题,本文将局部Savitzky-Golay(S-G)滤波、全局非对称高斯(Asymmetric Gaussian, AG)拟合原理和格拉布斯(Grubbs)检验算法相结合,构建Hyb-F组合式滤波法,重构向海自然保护区8种覆被类型的Landsat NDVI时间序列。首先,通过设定指标阈值剔除序列部分无效值;其次,采用引入Grubbs检验的S-G算法,剔除局部异常值;再次,采用引入Grubbs检验的AG拟合算法,剔除全局异常值;最后,利用S-G滤波算法平滑曲线,得到最终拟合结果。研究表明,该算法对灌木林地、草地、乔木林地和旱田等有植被生长覆被类型样本的拟合结果与纯净数据间相关性较强,相关系数(CC)达0.8488~0.9215,均方根误差(RMSE)为0.0429~0.1057。对盐碱地、建设用地、水域等非植被生长类型的数据具有较好的平滑作用。该算法对整个研究区数据重建效率指数为0.59,可有效地模拟原始数据。相比于单一滤波算法,Hyb-F滤波法具有更强的噪声识别能力,降低噪声引起的峰值损失,不仅能更好地模拟植被生长规律,并且能保留曲线细部特征,获得较高拟合精度。

关键词: 遥感, 组合滤波算法, Savitzky-Golay滤波, 非对称高斯拟合, 格拉布斯检验, 归一化植被指数时间序列

Abstract: Normalized Difference Vegetation Index (NDVI) time series exactly derived from remote sensing data are usually contaminated by different types of noise. Only by adopting the local or global filtering algorithm can not eliminate all kinds of noise from NDVI time series and maintain their local or global characters at the same time. A hybrid filtering algorithm, called Hyb-F, is proposed based on Savitzky-Golay filter, Asymmetric Gaussian algorithm and the Grubbs test method. Then, Hyb-F, which is a four step method, is used to reconstruct the Landsat NDVI time series for eight land cover types within Xianghai National Natural Reserve. First, the obvious outliers are detected and removed by setting thresholds for Normalized Difference Snow Index (NDSI), standard deviation and boundaries of NDVI. Second, via combing Grubbs test and Savitzky-Golay filter, the local outliers are removed. Third, via combing Grubbs test and Assymmetric Gaussian algorithm, the global outliers are removed. Finally, the final NDVI time series are built by using the Savitzky-Golay filter. The shape of fitting curves, statistical indicators and regional application effect of Hyb-F are analyzed. The results of the proposed Hyb-F method are compared with that of only Savitzky-Golay filter or Asymmetric Gaussian algorithm. For the land cover types with vegetation, Hyb-F performs well to the samples of shrub land, grassland, forest and cropland. Results of the mentioned types show large correlation with the clean reference series. The correlation coefficients are from 0.8488 to 0.9215 and the root mean square errors are from 0.0429 to 0.1057. The results of the first two land cover types achieve the highest accuracy among all the methods discussed. For the types without vegetation, such as saline, construction land and water area, the Hyb-F method can smooth the curves well. Compared with other methods, Fyb-F takes all local and global characters and dynamic trends into consideration. It can effectively recognize different types of outliers. Besides, it can weaken the loss of peak values and model the annual growing pattern of land cover types with vegetation. When applied to the whole study region, the indicator of efficiency of reconstruction is 0.59, demonstrating the reliability of Fyb-F. Moreover, the work flow the proposed method is clear and it is easy for application.

Key words: remote sensing, hybrid filtering algorithm, Savitzky-Golay filter, asymmetric Gaussian, Grubbs test, NDVI time series

中图分类号:

TP79

刘舒, 姜琦刚, 朱航, 李晓东. 基于Hyb-F组合滤波算法的向海自然保护区NDVI时间序列重构[J]. 吉林大学学报(工学版), 2018, 48(3): 957-967.

LIU Shu, JIANG Qi-gang, ZHU Hang, LI Xiao-dong. Reconstruction of Landsat NDVI time series of Xianghai natural deserve based on a hybrid filtering algorithm Hyb-F[J]. 吉林大学学报(工学版), 2018, 48(3): 957-967.

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