3.3.3. Tests with Satellite Data

Since snow is prevalent, a direct comparison of VI in snow-covered and snow-free pixels is difficult. Based on the simulation results, the effect of snow cover on SOS detection was analyzed from satellite data in two aspects. First, the statistical distribution of the minimum and maximum values of VI over time for each SCDr interval in each elevation zone was analyzed. This analysis could help reveal the difference in VI values between different SCDr intervals in the same elevation zone. Second, the statistical distribution of the SOS detected from real satellite data for different SCDc and ESS scenarios was analyzed, which could help reveal the variations in the detected SOS under different SCDc and ESS cases.

The flowchart of this study is shown in Figure 5.

**Figure 5.** Flowchart of the investigation of the effect of snow cover on spring phenology detection.
