*2.4. Water Body Data*

The water body data of GSWE came from a 30 m dataset produced based on optical images from Landsat satellites [28], with global coverage. GSWE released several subdatasets, including Occurrence, Change, Seasonality, Recurrence, etc. Each sub-dataset consisted of a 10◦ × 10◦ grid with a total range of 60◦S~80◦N and 180◦W~180◦E. The "Seasonality" product was selected for this study, and the individual pixel values were classified on a scale of 1 to 12, indicating how many months of the year were inundated with water. In this case, all values greater than 1 were labeled as water bodies to facilitate the exclusion of observations influenced by water bodies. Since this study was in the southern region of the United States, a total of 12 Seasonality data were selected for the range of 30◦N to 50◦N and 130◦W to 70◦W. A Seasonality product from these data was shown in Figure 2. Due to the special and static nature for the time-resolution of Landsat data, the produced GSWE dataset could not be synchronized with the observation time of CYGNSS. However, this dataset could remove the observations affected by water bodies to some extent.

**Figure 2.** The diagram of "Seasonality" product data of GSWE (0 represents no data).
