# Uncertainty Analysis of Multisource Land Cover Products in China
## 4 Discussion
Quantitative land cover monitoring was provided by VCF products, which solved the problem that land cover products could not capture subpixel and intrapixel changes. VCF products were also determined by the scientific community as earth system data records (ESDRs), but the current VCF data version only has three data layers, and further detailed land cover type monitoring cannot be provided. The reliability of our results was confirmed by similar studies. Different land cover product classification systems, sources, and precisions were different, and the differences between products were also significant, especially the differences in nontree vegetation, and the classification systems of different products were different, such as in the Qinghai-Tibet Plateau. MODIS products had little vegetation coverage, and some products had more grass coverage [39]. In this research, the semiquantitative ESA CCI product based on PFTs was more reliable. First, compared to other products, the ESA CCI had good spatial resolution [40]. Due to the limitation of spatial resolution, the image contained mixed pixels  
Figure 9: Conceptual illustration of (**a**–**c**) three types of land cover product characteristics and (**d**,**e**) consistency variations with resolution. of different land cover types. This may have led to uncertain results, but the PFT-based method quantified each land cover type, giving it quantitative characteristics [41]. Due to its qualitative and quantitative characteristics, it had good consistency with qualitative and quantitative products. In order to enrich our study, more products were compared. Since only one semiquantitative product and one quantitative product were available at present, we selected an additional qualitative ChinaLC product for comparison. The ChinaLC products used a large-scale classification approach to produce a decadal 5 km resolution land cover dataset from 1981 to 2010. A total of 19 classes of training and validation samples were obtained. The ChinaLC dataset has an average overall accuracy of approximately 75% [42]. However, the years of these products were not continuous, and it was difficult to conduct the trend analysis. We used the ChinaLC products to compare with the other three products. The percentage of the forest cover of the four products was calculated first, and then the two products were differentiated pixel-by-pixel, the resolution was 0.2\({}^{\circ}\), as shown in Figure 10. The spatial distribution of the forest cover of the four products was relatively consistent but differed significantly in different regions. The semiquantitative ESA CCI product had the highest consistency with the qualitative VCF product. This study used three types of land cover products in China from 2001 to 2012 and explored their uncertainties. The development of land cover products was as follows: Qualitative to quantitative and rough to fine. Quantitative land cover products could be used to quantitatively describe the climate, carbon, and sustainability [43]. However, only three data layers were included in the current quantitative VCF product, version 1.0, and the time frame reached only to 2015. Due to the lack of long-term records and the lack of intermediate years, the semiquantitative ESA CCI product is currently a better choice. VCF products had fewer data layers, the \"shrubs,\" \"grassland,\" and \"farmland\" in ESA CCI products were all classified as \"nontree vegetation.\" In fact, more detailed and specific category consistency is worthy of further study. We investigated the uncertainty of the grassland and farmland of MODIS and ESA CCI and found that the conclusions reached  
Figure 10: Spatial difference in forest coverage changes among the four products “ChinaLC\(-\)MODIS” represents the difference between the forest percentage of ChinaLC and MODIS products. The darker the color, the greater the product difference. were consistent with forests and nontree vegetation.