Validation of synthetic daily Landsat NDVI time series data generated by the improved spatial and temporal data fusion approach

摘要

Highlights?Daily 30m data were generated by combining MODIS and Landsat data.?A temporal validation method for synthetic daily 30m data was proposed and tested.?Vegetation phenology was monitored using synthetic daily Landsat NDVI data.?Phenology was monitored at 30m spatial resolution while the MODIS product is 500m.?A method for applying ISTDFA when land cover type changes was proposed.AbstractCorrelation analysis has been widely used to validate the accuracy of synthetic medium-resolution data generated by spatial and temporal fusion methods. However, as the temporal resolution of Landsat data is 16 days, this method only can be used for the validation of multi-temporal Landsat data. This means that the fusion accuracy of most images in a synthetic daily time series have not been validated. Furthermore, the fusion accuracy of each image in a synthetic Landsat time series is different, because there is a negative correlation with the time interval length between the fusion date and the base image date. Therefore, there is a need for temporal validation of synthetic daily Landsat time series data. We propose a suitable validation method in this paper. The improved spatial and temporal data fusion approach (ISTDFA) was applied to generate synthetic daily Landsat Normalized Difference Vegetation Index (NDVI) time series, which were then validated for both spatial and temporal dimensions using actual MODIS NDVI time series. For temporal validation, the correlation coefficients (R) between the actual and synthetic 500m NDVI time series were calculated by pixel-by-pixel to generate imagery with anRvalue for each pixel. For spatial validation,Rbetween MODIS NDVI imagery and synthetic Landsat NDVI imagery was calculated day by day to generate anRtime series. This method was tested and validated in two locations (Bole and Luntai) in Xinjiang Province, China. The results show that, for temporal validation, theRvalues of 86.08% pixels in Bole and 94.71% pixels in Luntai are higher than 0.9, and in spatial validation,Rvalues are higher than 0.8 on most days. Synthetic daily Landsat NDVI data was used to monitor the phenology of vegetation at a spatial resolution of 30m successfully, while the MODIS product is limited to 500m.]]>