## 4 Results
### Spatial Distribution and Temporal Variation in the Global Time-Share Two-Stage CI  
Figure 8 shows the global distributions of the multiyear average time-share two-stage CIs for both the LOS and LFS during the first vegetation cycle. In general, the spatial distributions of the global time-share two-stage CIs for both the LOS and LFS shows a similar pattern to that of IGBP classes (Figure 1), with lower CI values for forests and higher CI values for grasslands. Needleleaf forests in North America and Eurasia are distributed near 60\({}^{\circ}\)N latitude, and evergreen broadleaf forests in tropical rainforest regions present lower CIs, generally below 0.65. Grasslands in Inner Mongolia, China, the Midwestern United States, and equatorial Africa display higher CIs, approximately 0.78. Open shrublands in southern Africa and northern Eurasia also presented higher CIs, typically above 0.80. Therefore, the CI is not only related to phenological stage but also strongly correlated with land cover type and spatial distribution. Additionally, a comparison between Figures 8a and 8b reveals that the CI\({}_{\text{LOS}}\) is generally smaller than the CI\({}_{\text{LFS}}\) worldwide, indicating pronounced seasonal variation in the CI. This further supports the conclusion that CI is lower and that the clumping effect is stronger during LOS, whereas CI is greater and the clumping effect is weaker during LFS. Figure 8: Global distribution of multiyear average time-share two-stage CIs for (**a**) LOS and (**b**) LFS in the first vegetation cycle from 2001 to 2020. Figure 9 compares the multiyear average \(\mathrm{CL_{LOS}}\) and \(\mathrm{CL_{LFS}}\) across different land cover types from 2001 to 2020. Generally, the \(\mathrm{CL_{LOS}}\) is smaller than the \(\mathrm{CL_{LFS}}\) across all land cover types, which is consistent with the characteristics shown in Figure 8, suggesting that CIs across all land cover types exhibit significant seasonal variations at the global scale. Among these forests, needleleaf forests presented the lowest CI values, with minimal differences between the \(\mathrm{CL_{LOS}}\) and \(\mathrm{CL_{LFS}}\), indicating a high degree of clumping during both the LOS and LFS. The CI values of broadleaf forests are slightly greater than those of needleleaf forests, with a greater difference between the \(\mathrm{CI_{LOS}}\) and \(\mathrm{CL_{LFS}}\), indicating more distinct seasonal variations. This is because the clustered structure of needleleaf forests leads to a stronger clumping effect, and needle leaves have a lower renewal frequency [35; 67], resulting in more conservative seasonal variations in CI. Osh has the highest CI values, with a multiyear average \(\mathrm{CL_{LOS}}\) of 0.80 and \(\mathrm{CL_{LFS}}\) of 0.86. CSh, GL, PWe, CL, UB, and CVM also presented relatively high CI values, whereas broadleaf forests, MF, Wsa, and Sav presented relatively low CI values. As shown in Figure 10a,b, the QA distribution of the time-share two-stage CI product during LOS is better than that during LFS, with QA predominantly at 0 and 1, accounting for over 90%, which is significantly greater than that during LFS (\(\sim\)60%). During LFS, the QA of the time-share two-stage CI product is lower, and the time-share two-stage CIs with low QA are primarily distributed in high-latitude regions (50-90\({}^{\circ}\)N), with a significant presence of fill values. In addition, a considerable number of fill values are present in the mid-to-low latitude regions (\(-\)30\({}^{\circ}\) to 30\({}^{\circ}\)N) (Figure 10a,b), primarily due to the contamination of clouds and aerosols [47]. Figure 10c,d illustrate that the QA of the time-share two-stage CI product from 2001 to 2020 was relatively consistent. During LOS, except for a slightly lower proportion of QA = 0 in 2001-2002, the percentage remained at approximately 73% in the following years, whereas the proportion of QA values between 3 and 4 remained consistently low, at approximately 8%.