# Uncertainty Analysis of Multisource Land Cover Products in China
## 3 Results
### Uncertainty of Temporal and Spatial Changes  
The uncertainty of the spatial and temporal changes in the forest cover of the three products was studied, the pixel-by-pixel forest coverage of different resolutions from 2001 to 2012 was subjected to least squares regression, and the results are shown in Figure 5a. The forest increased slightly (<0.02/yr). The increase in forest mainly occurred in the northeast plain and inland China, and the loss mainly occurred on the southeast coast. The spatiotemporal changes in the forest were consistent, but the spatiotemporal changes in the forest derived from different products in different regions were quite different, and there was great uncertainty. In the ESA CCI products, there was an increase in forests (<0.02/yr) in China's Xinjiang Basin and Qinghai-Tibet Plateau. The other two products did not show this change. In the VCF product, there was a larger area of forest increase in the North China Plain (<0.04/yr), while the other two products did not show this change. When the spatiotemporal changes in the forests were considered, the qualitative VCF product was better, and the result was between qualitative products and semiquantitative products, which can qualitatively reflect the spatiotemporal changes in the forest. The impact of the resolution on product uncertainty was explored, and the percentage of various pixel changes with the resolution was counted. As the resolution decreased, the products tended to be consistent. The average percentage of pixels with forest increases of less than 0.02/yr for the three products was 50%. At a resolution of 0.1\({}^{\circ}\), the percentages of pixels with forest increases of less than 0.02/yr for the ESA CCI and MODIS products were 38 and 73%, respectively. When the resolution was reduced to 0.3\({}^{\circ}\), their pixel ratios were 46 and 62%. As the resolution decreased, they both approached 50%. As the resolution decreased, the uncertainty between products also decreased. The various pixels of VCF products did not change much with changes in the spatial resolution and were not sensitive to changes in the resolution. When the scale increased and decreased, there was no significant uncertainty. The uncertainty of the spatial and temporal changes in the forest cover of the three products was studied, and the results are shown in Figure 6a. The spatial and temporal variations in nontree vegetation derived from different products in different regions were quite different, the consistency of each product was low, and the uncertainty was large. The loss of nontree vegetation in coastal areas was severe (>0.02/yr), and the increase mainly occurred in western China, such as the Northeast Plain, Xinjiang Basin, and Qinghai-Tibet Plateau (<0.1/yr). The opposite conclusion may be drawn for different products in the same area. In the ESA CCI products, there was a decrease in nontree vegetation on the North China Plain (>0.02/yr), while in the MODIS products, there was an increase (0-0.02/yr). VCF qualitative products were highly sensitive to the temporal and spatial changes in nontree vegetation, and MODIS qualitative products were the least sensitive. The impact of resolution on product uncertainty was explored, and the percentage of various pixel changes with the resolution was counted. As the resolution decreased, the products tended to be consistent. The various pixels of the quantitative VCF product did not change much with the change in the spatial resolution and were not sensitive to the change in the resolution. When the scale increased and decreased, there was no significant uncertainty. The uncertainty of the spatial and temporal changes in the grass and crop cover were investigated. The pixel-by-pixel grass and crop coverage of different resolutions from 2001 to 2012 were subjected to least squares regression, as shown in Figure 7. The impact of the resolution on product uncertainty was explored. As the resolution decreased, the products tended to be consistent. The crop and grass increased slightly (<0.02/yr).